xenial (1) circus.1.gz

Provided by: circus_0.12.1+dfsg-1_all bug

NAME

       circus - Circus Documentation [image]

       Circus is a Python program which can be used to monitor and control processes and sockets.

       Circus can be driven via a command-line interface, a web interface or programmatically through its python
       API.

       To install it and try its features check out the examples, or read the rest of  this  page  for  a  quick
       introduction.

RUNNING A CIRCUS DAEMON

       Circus  provides a command-line script call circusd that can be used to manage processes organized in one
       or more watchers.

       Circus' command-line tool is configurable using an ini-style configuration file.

       Here's a very minimal example:

          [watcher:program]
          cmd = python myprogram.py
          numprocesses = 5

          [watcher:anotherprogram]
          cmd = another_program
          numprocesses = 2

       The file is then passed to circusd:

          $ circusd example.ini

       Besides processes, Circus can also bind sockets. Since every process managed by Circus is a child of  the
       main Circus daemon, that means any program that's controlled by Circus can use those sockets.

       Running a socket is as simple as adding a socket section in the config file:

          [socket:mysocket]
          host = localhost
          port = 8080

       To learn more about sockets, see sockets.

       To understand why it's a killer feature, read whycircussockets.

CONTROLLING CIRCUS

       Circus provides two command-line tools to manage your running daemon:

       • circusctl, a management console you can use to perform actions such as adding or removing workers

       • circus-top, a top-like console you can use to display the memory and cpu usage of your running Circus.

       To learn more about these, see cli

       Circus  also  offers  a web dashboard that can connect to a running Circus daemon and let you monitor and
       interact with it.

       To learn more about this feature, see circushttpd

   What now ?
       If you are a developer and want to leverage Circus in your own project, write plugins  or  hooks,  go  to
       fordevs.

       If you are an ops and want to manage your processes using Circus, go to forops.

   Contributions and Feedback
       More on contributing: contribs.

       Useful Links:

       • There's a mailing-list for any feedback or question: http://tech.groups.yahoo.com/group/circus-dev/

       • The repository and issue tracker are on GitHub : https://github.com/circus-tent/circus

       • Join us on the IRC : Freenode, channel #circus-tent

   Documentation index
   Installing Circus
       Circus is a Python package which is published on PyPI - the Python Package Index.

       The simplest way to install it is to use pip, a tool for installing and managing Python packages:

          $ pip install circus

       Or download the archive on PyPI, extract and install it manually with:

          $ python setup.py install

       If you want to try out Circus, see the examples.

       If  you  are  using  debian or any debian based distribution, you also can use the ppa to install circus,
       it's at https://launchpad.net/~roman-imankulov/+archive/circus

   zc.buildout
       We provide a zc.buildout configuration, you can use it by  simply  running  the  bootstrap  script,  then
       calling buildout:

          $ python bootstrap.py
          $ bin/buildout

   More on Requirements
       Circus works with:

       • Python 2.6, 2.7, 3.2 or 3.3

       •

         zeromq >= 2.1.10

                • The version of zeromq supported is ultimately determined by what version of pyzmq is installed
                  by pip during circus installation.

                • Their current release supports 2.x (limited), 3.x, and 4.x ZeroMQ versions.

                • Note: If you are using PyPy instead of CPython, make sure to read their installation  docs  as
                  ZeroMQ version support is not the same on PyPy.

       When you install circus, the latest versions of the Python dependencies will be pulled out for you.

       You can also install them manually using the pip-requirements.txt file we provide:

          $ pip install -r pip-requirements.txt

       If you want to run the Web console you will need to install circus-web:

          $ pip install circus-web

   Tutorial
   Step-by-step tutorial
       The  examples directory in the Circus  repository contains many examples to get you started, but here's a
       full tutorial that gives you an overview of the features.

       We're going to supervise a WSGI application.

   Installation
       Circus is tested on Mac OS X and Linux with the latest Python 2.6, 2.7, 3.2  and  3.3.   To  run  a  full
       Circus, you will also need libzmq, libevent & virtualenv.

       On Debian-based systems:

          $ sudo apt-get install libzmq-dev libevent-dev python-dev python-virtualenv

       Create a virtualenv and install circus, circus-web and chaussette in it

          $ virtualenv /tmp/circus
          $ cd /tmp/circus
          $ bin/pip install circus
          $ bin/pip install circus-web
          $ bin/pip install chaussette

       Once this is done, you'll find a plethora of commands in the local bin dir.

   Usage
       Chaussette comes with a default Hello world app, try to run it:

          $ bin/chaussette

       You should be able to visit http://localhost:8080 and see hello world.

       Stop Chaussette and add a circus.ini file in the directory containing:

          [circus]
          statsd = 1
          httpd = 1

          [watcher:webapp]
          cmd = bin/chaussette --fd $(circus.sockets.web)
          numprocesses = 3
          use_sockets = True

          [socket:web]
          host = 127.0.0.1
          port = 9999

       This  config file tells Circus to bind a socket on port 9999 and run 3 chaussettes workers against it. It
       also activates the Circus web dashboard and the statistics module.

       Save it & run it using circusd:

          $ bin/circusd --daemon circus.ini

       Now visit http://127.0.0.1:9999, you should see the hello world app.  The  difference  now  is  that  the
       socket is managed by Circus and there are several web workers that are accepting connections against it.

       NOTE:
          The  load  balancing is operated by the operating system so you're getting the same speed as any other
          pre-fork web server like Apache or NGinx. Circus does not interfer with the data that goes through.

       You can also visit http://localhost:8080/ and enjoy the Circus web dashboard.

   Interaction
       Let's use the circusctl shell while the system is running:

          $ bin/circusctl
          circusctl 0.7.1
          circusd-stats: active
          circushttpd: active
          webapp: active
          (circusctl)

       You get into an interactive shell. Type help to get all commands:

          (circusctl) help

          Documented commands (type help <topic>):
          ========================================
          add     get            list         numprocesses  quit     rm      start   stop
          decr    globaloptions  listen       numwatchers   reload   set     stats
          dstats  incr           listsockets  options       restart  signal  status

          Undocumented commands:
          ======================
          EOF  help

       Let's try basic things. Let's list the web workers processes and add a new one:

          (circusctl) list webapp
          13712,13713,13714
          (circusctl) incr webapp
          4
          (circusctl) list webapp
          13712,13713,13714,13973

       Congrats, you've interacted with your Circus! Get off the shell with Ctrl+D and now run circus-top:

          $ bin/circus-top

       This is a top-like command to watch all your processes' memory and CPU usage in real time.

       Hit Ctrl+C and now let's quit Circus completely via circus-ctl:

          $ bin/circusctl quit
          ok

   Next steps
       You can plug your own WSGI application instead  of  Chaussette's  hello  world  simply  by  pointing  the
       application callable.

       Chaussette also comes with many backends like Gevent or Meinheld.

       Read https://chaussette.readthedocs.org/ for all options.

   Why should I use Circus instead of X ?
       1. Circus simplifies your web stack process management

          Circus knows how to manage processes and sockets, so you don't have to delegate web workers management
          to a WGSI server.

          See whycircussockets

       2. Circus provides pub/sub and poll notifications via ZeroMQ
          Circus has a pub/sub channel you can subscribe to. This  channel  receives  all  events  happening  in
          Circus. For example, you can be notified when a process is flapping, or build a client that triggers a
          warning when some processes are eating all the CPU or RAM.

          These events are sent via a ZeroMQ channel, which makes it different from the stdin stream Supervisord
          uses:

          • Circus  sends  events  in a fire-and-forget fashion, so there's no need to manually loop through all
            listeners and maintain their states.

          • Subscribers can be located on a remote host.

          Circus also provides ways to get status updates via one-time polls on a req/rep  channel.  This  means
          you  can  get  your  information  without having to subscribe to a stream. The cli command provided by
          Circus uses this channel.

          See examples.

       3. Circus is (Python) developer friendly
          While Circus can be driven entirely by a config file and the circusctl / circusd commands, it is  easy
          to reuse all or part of the system to build your own custom process watcher in Python.

          Every layer of the system is isolated, so you can reuse independently:

          • the process wrapper (Process)

          • the processes manager (Watcher)

          • the global manager that runs several processes managers (Arbiter)

          • and so on…

       4. Circus scales
          One  of  the  use cases of Circus is to manage thousands of processes without adding overhead -- we're
          dedicated to focusing on this.

   Coming from Supervisor
       Supervisor is a very popular solution in the Python world and we're often asked how Circus compares  with
       it.

       If you are coming from Supervisor, this page tries to give an overview of how the tools differ.

   Differences overview
       Supervisor  & Circus have the same goals - they both manage processes and provide a command-line script —
       respectively supervisord and circusd — that reads a configuration file, forks new processes and keep them
       alive.

       Circus  has an extra feature: the ability to bind sockets and let the processes it manages use them. This
       "pre-fork" model is used by many web servers out there, like Apache or Unicorn.  Having  this  option  in
       Circus can simplify a web app stack: all processes and sockets are managed by a single tool.

       Both  projects  provide a way to control a running daemon via another script.  respectively supervisorctl
       and circusctl. They also both have events and a way to subscribe to them.  The  main  difference  is  the
       underlying technology: Supervisor uses XML-RPC for interacting with the daemon, while Circus uses ZeroMQ.

       Circus  &  Supervisor  both  have  a  web  interface to display what's going on. Circus' is more advanced
       because you can follow in real time what's going on and interact with the daemon. It uses web sockets and
       is developed in a separate project (circus-web.)

       There  are many other subtle differences in the core design, we might list here one day… In the meantime,
       you can learn more about circus internals in design.

   Configuration
       Both systems use an ini-like file as a configuration.

       • Supervisor documentationCircus documentation

       Here's a small example of running an application with Supervisor. In this case, the application  will  be
       started and restarted in case it crashes

          [program:example]
          command=npm start
          directory=/home/www/my-server/
          user=www-data
          autostart=true
          autorestart=true
          redirect_stderr=True

       In Circus, the same configuration is done by:

          [watcher:example]
          cmd=npm start
          working_dir=/home/www/my-server/
          user=www-data
          stderr_stream.class=StdoutStream

       Notice that the stderr redirection is slightly different in Circus. The tool does not have a tail feature
       like in Supervisor, but will let you hook any piece of code to deal with the  incoming  stream.  You  can
       create  your  own  stream  hook  (as  a  Class) and do whatever you want with the incoming stream. Circus
       provides  some  built-in  stream   classes   like   StdoutStream,   FileStream,   WatchedFileStream,   or
       TimedRotatingFileStream.

   Circus for Ops
       WARNING:
          By default, Circus doesn't secure its messages when sending information through ZeroMQ. Before running
          Circus in a production environment, make sure to read the Security page.

       The first step to manage a Circus daemon is to write its configuration file.  See configuration.  If  you
       are deploying a web stack, have a look at sockets.

       Circus can be deployed using Python 2.6, 2.7, 3.2 or 3.3 - most deployments out there are done in 2.7. To
       learn how to deploy Circus, check out deployment.

       To manage a Circus daemon, you should get familiar with the list of commands you can  use  in  circusctl.
       Notice that you can have the same help online when you run circusctl as a shell.

       We also provide circus-top, see cli and a nice web dashboard. see circushttpd.

       Last, to get the most out of Circus, make sure to check out how to use plugins and hooks. See plugins and
       hooks.

   Ops documentation index
   Configuration
       Circus can be configured using an ini-style configuration file.

       Example:

          [circus]
          check_delay = 5
          endpoint = tcp://127.0.0.1:5555
          pubsub_endpoint = tcp://127.0.0.1:5556
          include = \*.more.config.ini
          umask = 002

          [watcher:myprogram]
          cmd = python
          args = -u myprogram.py $(circus.wid) $(CIRCUS.ENV.VAR)
          warmup_delay = 0
          numprocesses = 5

          # hook
          hooks.before_start = my.hooks.control_redis

          # will push in test.log the stream every 300 ms
          stdout_stream.class = FileStream
          stdout_stream.filename = test.log

          # optionally rotate the log file when it reaches 1 gb
          # and save 5 copied of rotated files
          stdout_stream.max_bytes = 1073741824
          stdout_stream.backup_count = 5

          [env:myprogram]
          PATH = $PATH:/bin
          CAKE = lie

          [plugin:statsd]
          use = circus.plugins.statsd.StatsdEmitter
          host = localhost
          port = 8125
          sample_rate = 1.0
          application_name = example

          [socket:web]
          host = localhost
          port = 8080

   circus - single section
          endpoint
                 The ZMQ socket used to manage Circus via circusctl.  (default: tcp://127.0.0.1:5555)

          endpoint_owner
                 If set to a system username and the endpoint is an ipc socket like  ipc://var/run/circusd.sock,
                 then  ownership  of  the socket file will be changed to that user at startup. For more details,
                 see security.  (default: None)

          pubsub_endpoint
                 The ZMQ PUB/SUB socket receiving publications of events.  (default: tcp://127.0.0.1:5556)

          papa_endpoint
                 If using papa, you can specify the endpoint,  such  as  ipc://var/run/circusd.sock.   (default:
                 tcp://127.0.0.1:20202)

          statsd If set to True, Circus runs the circusd-stats daemon. (default: False)

          stats_endpoint
                 The ZMQ PUB/SUB socket receiving publications of stats.  (default: tcp://127.0.0.1:5557)

          statsd_close_outputs
                 If True sends the circusd-stats stdout/stderr to /dev/null.  (default: False)

          check_delay
                 The polling interval in seconds for the ZMQ socket. (default: 5)

          include
                 List  of  config  files to include. You can use wildcards (*) to include particular schemes for
                 your files. The paths are absolute or relative to the config file. (default: None)

          include_dir
                 List of config directories. All files matching *.ini under each directory will be included. The
                 paths are absolute or relative to the config file. (default: None)

          stream_backend
                 Defines  the  type  of  backend to use for the streaming. Possible values are thread or gevent.
                 (default: thread)

          warmup_delay
                 The interval in seconds between two watchers start. Must be an int. (default: 0)

          httpd  If set to True, Circus runs the circushttpd daemon. (default: False)

          httpd_host
                 The host ran by the circushttpd daemon. (default: localhost)

          httpd_port
                 The port ran by the circushttpd daemon. (default: 8080)

          httpd_close_outputs
                 If True, sends the circushttpd stdout/stderr to /dev/null.  (default: False)

          debug  If set to True, all  Circus  stout/stderr  daemons  are  redirected  to  circusd  stdout/stderr
                 (default: False)

          debug_gc
                 If  set  to  True,  circusd outputs additional log info from the garbage collector. This can be
                 useful in tracking down memory leaks.  (default: False)

          pidfile
                 The file that must be used to keep the daemon pid.

          umask  Value for umask. If not set, circusd will not attempt to modify umask.

          loglevel
                 The loglevel that we want to see (default: INFO)

          logoutput
                 The logoutput file where we want to log (default: - to log on stdout). You can log to a  remote
                 syslog  by  using  the  following syntax: syslog://host:port?facility where host is your syslog
                 server, port is optional and facility is the syslog facility to use. If you wish to  log  to  a
                 local syslog you can use syslog:///path/to/syslog/socket?facility instead.

          loggerconfig
                 A  path to an INI, JSON or YAML file to configure standard Python logging for the Arbiter.  The
                 special value "default" uses the builtin logging configuration based on the  optional  loglevel
                 and logoutput options.

                 Example YAML Configuration File

              version: 1
              disable_existing_loggers: false
              formatters:
                simple:
                  format: '%(asctime)s - %(name)s - [%(levelname)s] %(message)s'
              handlers:
                logfile:
                  class: logging.FileHandler
                  filename: logoutput.txt
                  level: DEBUG
                  formatter: simple
              loggers:
                circus:
                  level: DEBUG
                  handlers: [logfile]
                  propagate: no
              root:
                level: DEBUG
                handlers: [logfile]

   watcher:NAME - as many sections as you want
          NAME   The name of the watcher. This name is used in circusctl

          cmd    The executable program to run.

          args   Command-line  arguments  to  pass  to the program. You can use the python format syntax here to
                 build the parameters. Environment variables are available, as well as the  worker  id  and  the
                 environment  variables  that  you  passed, if any, with the "env" parameter. See Formatting the
                 commands and arguments with dynamic variables for more information on this.

          shell  If True, the processes are run in the shell (default: False)

          shell_args
                 Command-line arguments to pass to the shell command when shell is True.  Works  only  for  *nix
                 system (default: None)

          working_dir
                 The working dir for the processes (default: None)

          uid    The user id or name the command should run with.  (The current uid is the default).

          gid    The group id or name the command should run with. (The current gid is the default).

          copy_env
                 If  set  to true, the local environment variables will be copied and passed to the workers when
                 spawning them. (Default: False)

          copy_path
                 If set to true, sys.path is passed in the subprocess environ using PYTHONPATH. copy_env has  to
                 be true.  (Default: False)

          warmup_delay
                 The delay (in seconds) between running processes.

          autostart
                 If  set  to  false,  the watcher will not be started automatically when the arbiter starts. The
                 watcher can be started explicitly (example: circusctrl start myprogram). (Default: True)

          numprocesses
                 The number of processes to run for this watcher.

          rlimit_LIMIT
                 Set resource limit LIMIT for the watched processes. The config name should match  the  RLIMIT_*
                 constants  (not  case  sensitive) listed in the Python resource module reference.  For example,
                 the config line 'rlimit_nofile = 500' sets the maximum number of open files to 500.  To  set  a
                 limit value to RLIM_INFINITY, do not set a value, like this config line: 'rlimit_nofile = '.

          stderr_stream.class
                 A  fully  qualified  Python  class  name that will be instanciated, and will receive the stderr
                 stream of all processes in its __call__() method.

                 Circus provides some stream classes you can use without prefix:

                 • FileStream: writes in a file and can do automatic log rotation

                 • WatchedFileStream: writes in a file and relies on external log rotation

                 • TimedRotatingFileStream: writes in a file and can do rotate at certain timed intervals.

                 • QueueStream: write in a memory Queue

                 • StdoutStream: writes in the stdout

                 • FancyStdoutStream: writes colored output with time prefixes in the stdout

          stderr_stream.*
                 All options starting with stderr_stream. other than class will be passed the  constructor  when
                 creating an instance of the class defined in stderr_stream.class.

          stdout_stream.class
                 A  fully  qualified  Python  class  name that will be instanciated, and will receive the stdout
                 stream of all processes in its __call__() method.

                 Circus provides some stream classes you can use without prefix:

                 • FileStream: writes in a file and can do automatic log rotation

                 • WatchedFileStream: writes in a file and relies on external log rotation

                 • TimedRotatingFileStream: writes in a file and can do rotate at certain timed intervals.

                 • QueueStream: write in a memory Queue

                 • StdoutStream: writes in the stdout

                 • FancyStdoutStream: writes colored output with time prefixes in the stdout

          stdout_stream.*
                 All options starting with stdout_stream. other than class will be passed the  constructor  when
                 creating an instance of the class defined in stdout_stream.class.

          close_child_stdout
                 If  set  to  True,  the stdout stream of each process will be sent to /dev/null after the fork.
                 Defaults to False.

          close_child_stderr
                 If set to True, the stderr stream of each process will be sent to  /dev/null  after  the  fork.
                 Defaults to False.

          send_hup
                 If True, a process reload will be done by sending the SIGHUP signal.  Defaults to False.

          stop_signal
                 The  signal  to  send when stopping the process. Can be specified as a number or a signal name.
                 Signal names are case-insensitive and can include 'SIG' or not. So valid examples include quit,
                 INT, SIGTERM and 3.  Defaults to SIGTERM.

          stop_children
                 When sending the stop_signal, send it to the children as well.  Defaults to False.

          max_retry
                 The  number  of  times  we  attempt  to  start  a process, before we abandon and stop the whole
                 watcher. Defaults to 5.  Set to -1 to disable max_retry and retry indefinitely.

          graceful_timeout
                 The number of seconds to wait for a process to terminate gracefully before killing it.

                 When stopping a process, we first send it a stop_signal. A worker  may  catch  this  signal  to
                 perform   clean   up   operations  before  exiting.   If  the  worker  is  still  active  after
                 graceful_timeout seconds, we send it a SIGKILL signal.  It is not  possible  to  catch  SIGKILL
                 signals so the worker will stop.

                 Defaults to 30s.

          priority
                 Integer  that  defines  a  priority for the watcher. When the Arbiter do some operations on all
                 watchers, it will sort them with this field, from the bigger number to the smallest.   Defaults
                 to 0.

          singleton
                 If set to True, this watcher will have at the most one process.  Defaults to False.

          use_sockets
                 If set to True, this watcher will be able to access defined sockets via their file descriptors.
                 If False, all parent fds are closed when the child process is forked. Defaults to False.

          max_age
                 If set then the process will be restarted sometime after max_age seconds. This is  useful  when
                 processes  deal  with  pool  of  connectors:  restarting processes improves the load balancing.
                 Defaults to being disabled.

          max_age_variance
                 If max_age is set  then  the  process  will  live  between  max_age  and  max_age  +  random(0,
                 max_age_variance) seconds. This avoids restarting all processes for a watcher at once. Defaults
                 to 30 seconds.

          on_demand
                 If set to True, the processes will be started only after the first connection  to  one  of  the
                 configured  sockets  (see below). If a restart is needed, it will be only triggered at the next
                 socket event.

          hooks.*
                 Available hooks: before_start, after_start, before_spawn, after_spawn, before_stop, after_stop,
                 before_signal, after_signal, extended_stats

                 Define callback functions that hook into the watcher startup/shutdown process.

                 If  the hook returns False and if the hook is one of before_start, before_spawn, after_start or
                 after_spawn, the startup will be aborted.

                 If the hook is before_signal and returns False, then the corresponding signal will not be  sent
                 (except SIGKILL which is always sent)

                 Notice that a hook that fails during the stopping process will not abort it.

                 The  callback  definition can be followed by a boolean flag separated by a comma. When the flag
                 is set to true, any error occuring in the hook will be ignored. If set to false (the  default),
                 the hook will return False.

                 More on hooks.

          virtualenv
                 When  provided,  points  to the root of a Virtualenv directory. The watcher will scan the local
                 site-packages and loads its content into the execution environment. Must be used with  copy_env
                 set to True. Defaults to None.

          virtualenv_py_ver
                 Specifies  the  python  version of the virtualenv (e.g "3.3").  It's usefull if circus run with
                 another python version (e.g "2.7") The  watcher  will  scan  the  local  site-packages  of  the
                 specified python version and load its content into the execution environment. Must be used with
                 virtualenv. Defaults to None.

          respawn
                 If set to False, the processes handled by a watcher will not be  respawned  automatically.  The
                 processes can be manually respawned with the start command. (default: True)

          use_papa
                 Set to true to use the papa.

   socket:NAME - as many sections as you want
          host   The host of the socket. Defaults to 'localhost'

          port   The port. Defaults to 8080.

          family The socket family. Can be 'AF_UNIX', 'AF_INET' or 'AF_INET6'.  Defaults to 'AF_INET'.

          type   The   socket   type.   Can   be   'SOCK_STREAM',   'SOCK_DGRAM',   'SOCK_RAW',   'SOCK_RDM'  or
                 'SOCK_SEQPACKET'. Defaults to 'SOCK_STREAM'.

          interface
                 When provided a network interface name like 'eth0', binds the socket to that particular  device
                 so that only packets received from that particular interface are processed by the socket.  This
                 can be used for example to limit which device to bind when binding on IN_ADDR_ANY (0.0.0.0)  or
                 IN_ADDR_BROADCAST  (255.255.255.255).  Note  that  this  only  works  for  some  socket  types,
                 particularly AF_INET sockets.

          path   When provided a path to a file that will be used as a unix socket file. If a path is  provided,
                 family is forced to AF_UNIX and host and port are ignored.

          umask  When  provided,  sets  the  umask  that  will be used to create an AF_UNIX socket. For example,
                 umask=000 will produce a socket with permission 777.

          replace
                 When creating Unix sockets ('AF_UNIX'), an existing file may indicate a problem so the  default
                 is  to  fail.  Specify  True  to  simply remove the old file if you are sure that the socket is
                 managed only by Circus.

          so_reuseport
                 If set to True and SO_REUSEPORT is available on target platform, circus will  create  and  bind
                 new SO_REUSEPORT socket(s) for every worker it starts which is a user of this socket(s).

          use_papa
                 Set to true to use the papa.

       Once a socket is created, the ${circus.sockets.NAME} string can be used in the command (cmd or args) of a
       watcher. Circus will replace it by the FD value. The watcher must  also  have  use_sockets  set  to  True
       otherwise the socket will have been closed and you will get errors when the watcher tries to use it.

       Example:

          [watcher:webworker]
          cmd = chaussette --fd $(circus.sockets.webapp) chaussette.util.bench_app
          use_sockets = True

          [socket:webapp]
          host = 127.0.0.1
          port = 8888

   plugin:NAME - as many sections as you want
          use    The fully qualified name that points to the plugin class.

          anything else
                 Every other key found in the section is passed to the plugin constructor in the config mapping.

                 You can use all the watcher options, since a plugin is started like a watcher.

       Circus comes with a few pre-shipped plugins but you can also extend them easily by developing your own.

   env or env[:WATCHERS] - as many sections as you want
          anything
                 The  name  of an environment variable to assign value to.  bash style environment substitutions
                 are supported.  for example, append /bin to PATH 'PATH = $PATH:/bin'

       Section responsible for delivering environment variable to run processes.

       Example:

          [watcher:worker1]
          cmd = ping 127.0.0.1

          [watcher:worker2]
          cmd = ping 127.0.0.1

          [env]
          CAKE = lie

       The variable CAKE will propagated to all watchers defined in config file.

       WATCHERS can be a comma separated list of watcher sections to apply this environment to.  if multiple env
       sections match a watcher, they will be combine in the order they appear in the configuration file.  later
       entries will take precedence.

       Example:

          [watcher:worker1]
          cmd = ping 127.0.0.1

          [watcher:worker2]
          cmd = ping 127.0.0.1

          [env:worker1,worker2]
          PATH = /bin

          [env:worker1]
          PATH = $PATH

          [env:worker2]
          CAKE = lie

       worker1 will be run with PATH = $PATH (expanded from the environment circusd was run in) worker2 will  be
       run with PATH = /bin and CAKE = lie

       It's possible to use wildcards as well.

       Example:

          [watcher:worker1]
          cmd = ping 127.0.0.1

          [watcher:worker2]
          cmd = ping 127.0.0.1

          [env:worker*]
          PATH = /bin

       Both worker1 and worker2 will be run with PATH = /bin

   Using environment variables
       When  writing your configuration file, you can use environment variables defined in the env section or in
       os.environ itself.

       You just have to use the circus.env. prefix.

       Example:

          [watcher:worker1]
          cmd = $(circus.env.shell)

          [watcher:worker2]
          baz = $(circus.env.user)
          bar = $(circus.env.yeah)
          sup = $(circus.env.oh)

          [socket:socket1]
          port = $(circus.env.port)

          [plugin:plugin1]
          use = some.path
          parameter1 = $(circus.env.plugin_param)

          [env]
          yeah = boo

          [env:worker2]
          oh = ok

       If a variable is defined in several places, the most specialized value has precedence: a variable defined
       in env:XXX will override a variable defined in env, which will override a variable defined in os.environ.

       environment substitutions can be used in any section of the configuration in any section variable.

   Formatting the commands and arguments with dynamic variables
       As  you may have seen, it is possible to pass some information that are computed dynamically when running
       the processes. Among other things, you can get the worker id (WID) and all the options that are passed to
       the Process.  Additionally, it is possible to access the options passed to the Watcher which instanciated
       the process.

       NOTE:
          The worker id is different from the process id. It's a unique value, starting  at  1,  which  is  only
          unique for the watcher.

       For  instance, if you want to access some variables that are contained in the environment, you would need
       to do it with a setting like this:

          cmd = "make-me-a-coffee --sugar $(CIRCUS.ENV.SUGAR_AMOUNT)"

       This works with both cmd and args.

       Important:

       • All variables are prefixed with circus.

       • The replacement is case insensitive.

   Stream configuration
       Simple stream class like QueueStream and StdoutStream don't  have  specific  attributes  but  some  other
       stream class may have some:

   FileStream
          filename
                 The file path where log will be written.

          time_format
                 The  strftime  format  that will be used to prefix each time with a timestamp.  By default they
                 will be not prefixed.

                 i.e: %Y-%m-%d %H:%M:%S

          max_bytes
                 The max size of the log file before a new file is started.  If not provided, the  file  is  not
                 rolled over.

          backup_count
                 The number of log files that will be kept By default backup_count is null.

       NOTE:
          Rollover  occurs whenever the current log file is nearly max_bytes in length. If backup_count is >= 1,
          the system will successively create new files with the same  pathname  as  the  base  file,  but  with
          extensions  ".1", ".2" etc. appended to it. For example, with a backup_count of 5 and a base file name
          of "app.log", you would get "app.log", "app.log.1", "app.log.2", ... through to "app.log.5". The  file
          being  written  to  is  always  "app.log"  -  when  it  gets  filled  up,  it is closed and renamed to
          "app.log.1", and if files "app.log.1", "app.log.2" etc.  exist, then they are renamed to  "app.log.2",
          "app.log.3" etc.  respectively.

       Example:

          [watcher:myprogram]
          cmd = python -m myapp.server

          stdout_stream.class = FileStream
          stdout_stream.filename = test.log
          stdout_stream.time_format = %Y-%m-%d %H:%M:%S
          stdout_stream.max_bytes = 1073741824
          stdout_stream.backup_count = 5

   WatchedFileStream
          filename
                 The file path where log will be written.

          time_format
                 The  strftime  format  that will be used to prefix each time with a timestamp.  By default they
                 will be not prefixed.

                 i.e: %Y-%m-%d %H:%M:%S

       NOTE:
          WatchedFileStream relies on an external log rotation tool to ensure that log files  don't  become  too
          big. The output file will be monitored and if it is ever deleted or moved by the external log rotation
          tool, then the output file handle will be automatically reloaded.

       Example:

          [watcher:myprogram]
          cmd = python -m myapp.server

          stdout_stream.class = WatchedFileStream
          stdout_stream.filename = test.log
          stdout_stream.time_format = %Y-%m-%d %H:%M:%S

   TimedRotatingFileStream
          filename
                 The file path where log will be written.

          backup_count
                 The number of log files that will be kept By default backup_count is null.

          time_format
                 The strftime format that will be used to prefix each time with a timestamp.   By  default  they
                 will be not prefixed.

                 i.e: %Y-%m-%d %H:%M:%S

          rotate_when
                 The  type  of  interval.   The  list  of  possible values is below. Note that they are not case
                 sensitive.

                                              ┌───────────┬───────────────────────┐
                                              │Value      │ Type of interval      │
                                              ├───────────┼───────────────────────┤
                                              │'S'        │ Seconds               │
                                              ├───────────┼───────────────────────┤
                                              │'M'        │ Minutes               │
                                              ├───────────┼───────────────────────┤
                                              │'H'        │ Hours                 │
                                              ├───────────┼───────────────────────┤
                                              │'D'        │ Days                  │
                                              ├───────────┼───────────────────────┤
                                              │'W0'-'W6'  │ Weekday (0=Monday)    │
                                              ├───────────┼───────────────────────┤
                                              │'midnight' │ Roll over at midnight │
                                              └───────────┴───────────────────────┘

          rotate_interval
                 The rollover interval.

       NOTE:
          TimedRotatingFileStream rotates logfiles at certain timed intervals.  Rollover interval is  determined
          by a  combination of rotate_when and rotate_interval.

       Example:

          [watcher:myprogram]
          cmd = python -m myapp.server

          stdout_stream.class = TimedRotatingFileStream
          stdout_stream.filename = test.log
          stdout_stream.time_format = %Y-%m-%d %H:%M:%S
          stdout_stream.utc = True
          stdout_stream.rotate_when = H
          stdout_stream.rotate_interval = 1

   FancyStdoutStream
          color

                 The name of an ascii color:

                        • red

                        • green

                        • yellow

                        • blue

                        • magenta

                        • cyan

                        • white

          time_format
                 The strftime format that each line will be prefixed with.

                 Default to: %Y-%m-%d %H:%M:%S

       Example:

          [watcher:myprogram]
          cmd = python -m myapp.server
          stdout_stream.class = FancyStdoutStream
          stdout_stream.color = green
          stdout_stream.time_format = %Y/%m/%d | %H:%M:%S

   Commands
       At  the  epicenter of circus lives the command systems.  circusctl is just a zeromq client, and if needed
       you can drive programmaticaly the Circus system by writing your own zmq client.

       All messages are JSON mappings.

       For each command below, we provide a usage example with  circusctl  but  also  the  input  /  output  zmq
       messages.

   circus-ctl commandsadd: commands/adddecr: commands/decrdstats: commands/dstatsget: commands/getglobaloptions: commands/globaloptionsincr: commands/incripython: commands/ipythonlist: commands/listlisten: commands/listenlistsockets: commands/listsocketsnumprocesses: commands/numprocessesnumwatchers: commands/numwatchersoptions: commands/optionsquit: commands/quitreload: commands/reloadreloadconfig: commands/reloadconfigrestart: commands/restartrm: commands/rmset: commands/setsignal: commands/signalstart: commands/startstats: commands/statsstatus: commands/statusstop: commands/stop

   Add a watcher
       This command add a watcher dynamically to a arbiter.

   ZMQ Message
          {
              "command": "add",
              "properties": {
                  "cmd": "/path/to/commandline --option"
                  "name": "nameofwatcher"
                  "args": [],
                  "options": {},
                  "start": false
              }
          }

       A message contains 2 properties:

       • cmd: Full command line to execute in a process

       • args: array, arguments passed to the command (optional)

       • name: name of watcher

       • options: options of a watcher

       • start: start the watcher after the creation

       The response return a status "ok".

   Command line
          $ circusctl add [--start] <name> <cmd>

   Options
       • <name>: name of the watcher to create

       • <cmd>: full command line to execute in a process

       • --start: start the watcher immediately

   Decrement the number of processes in a watcher
       This comment decrement the number of processes in a watcher by <nbprocess>, 1 being the default.

   ZMQ Message
          {
              "command": "decr",
              "propeties": {
                  "name": "<watchername>"
                  "nb": <nbprocess>
                  "waiting": False
              }
          }

       The response return the number of processes in the 'numprocesses` property:

          { "status": "ok", "numprocesses": <n>, "time", "timestamp" }

   Command line
          $ circusctl decr <name> [<nb>] [--waiting]

   Options
       • <name>: name of the watcher

       • <nb>: the number of processes to remove.

   Get circusd stats
       You can get at any time some statistics about circusd with the dstat command.

   ZMQ Message
       To get the circusd stats, simply run:

          {
              "command": "dstats"
          }

       The response returns a mapping the property "infos" containing some process informations:

          {
            "info": {
              "children": [],
              "cmdline": "python",
              "cpu": 0.1,
              "ctime": "0:00.41",
              "mem": 0.1,
              "mem_info1": "3M",
              "mem_info2": "2G",
              "nice": 0,
              "pid": 47864,
              "username": "root"
            },
            "status": "ok",
            "time": 1332265655.897085
          }

   Command Line
          $ circusctl dstats

   Get the value of specific watcher options
       This command can be used to query the current value of one or more watcher options.

   ZMQ Message
          {
              "command": "get",
              "properties": {
                  "keys": ["key1, "key2"]
                  "name": "nameofwatcher"
              }
          }

       A request message contains two properties:

       • keys: list, The option keys for which you want to get the values

       • name: name of watcher

       The response object has a property options which is a dictionary of option names and values.

       eg:

          {
              "status": "ok",
              "options": {
                  "graceful_timeout": 300,
                  "send_hup": True,
              },
              time': 1332202594.754644
          }

   Command line
          $ circusctl get <name> <key1> <key2>

   Get the arbiter options
       This command return the arbiter options

   ZMQ Message
          {
              "command": "globaloptions",
              "properties": {
                  "key1": "val1",
                  ..
              }
          }

       A message contains 2 properties:

       • keys: list, The option keys for which you want to get the values

       The  response  return  an  object  with a property "options" containing the list of key/value returned by
       circus.

       eg:

          {
              "status": "ok",
              "options": {
                  "check_delay": 1,
                  ...
              },
              time': 1332202594.754644
          }

   Command line
          $ circusctl globaloptions

   Options
       Options Keys are:

       • endpoint: the controller ZMQ endpoint

       • pubsub_endpoint: the pubsub endpoint

       • check_delay: the delay between two controller points

       • multicast_endpoint: the multicast endpoint for circusd cluster auto-discovery

   Increment the number of processes in a watcher
       This comment increment the number of processes in a watcher by <nbprocess>, 1 being the default

   ZMQ Message
          {
              "command": "incr",
              "properties": {
                  "name": "<watchername>",
                  "nb": <nbprocess>,
                  "waiting": False
              }
          }

       The response return the number of processes in the 'numprocesses` property:

          { "status": "ok", "numprocesses": <n>, "time", "timestamp" }

   Command line
          $ circusctl incr <name> [<nb>] [--waiting]

   Options
       • <name>: name of the watcher.

       • <nb>: the number of processes to add.

   Create shell into circusd process
       This command is only useful if you have the ipython package installed.

   Command Line
          $ circusctl ipython

   Get list of watchers or processes in a watcher
   ZMQ Message
       To get the list of all the watchers:

          {
              "command": "list",
          }

       To get the list of active processes in a watcher:

          {
              "command": "list",
              "properties": {
                  "name": "nameofwatcher",
              }
          }

       The response return the list asked. the mapping returned can either be 'watchers' or 'pids' depending the
       request.

   Command line
          $ circusctl list [<name>]

   Subscribe to a watcher event
   ZMQ
       At  any  moment  you can subscribe to a circus event. Circus provides a PUB/SUB feed on which any clients
       can subscribe. The subscriber endpoint URI is set in the circus.ini configuration file.

       Events are pubsub topics:

       • watcher.<watchername>.reap: when a process is reaped

       • watcher.<watchername>.spawn: when a process is spawned

       • watcher.<watchername>.kill: when a process is killed

       • watcher.<watchername>.updated: when watcher configuration is updated

       • watcher.<watchername>.stop: when a watcher is stopped

       • watcher.<watchername>.start: when a watcher is started

       All events messages are in a json struct.

   Command line
       The client has been updated to provide a simple way to listen on the events:

          circusctl listen [<topic>, ...]

   Example of result:
          $ circusctl listen tcp://127.0.0.1:5556
          watcher.refuge.spawn: {u'process_id': 6, u'process_pid': 72976,
                                 u'time': 1331681080.985104}
          watcher.refuge.spawn: {u'process_id': 7, u'process_pid': 72995,
                                 u'time': 1331681086.208542}
          watcher.refuge.spawn: {u'process_id': 8, u'process_pid': 73014,
                                 u'time': 1331681091.427005}

   Get the list of sockets
   ZMQ Message
       To get the list of sockets:

          {
              "command": "listsockets",
          }

       The response return a list of json mappings with keys for fd, name, host and port.

   Command line
          $ circusctl listsockets

   Get the number of processes
       Get the number of processes in a watcher or in a arbiter

   ZMQ Message
          {
              "command": "numprocesses",
              "propeties": {
                  "name": "<watchername>"
              }

          }

       The response return the number of processes in the 'numprocesses` property:

          { "status": "ok", "numprocesses": <n>, "time", "timestamp" }

       If the property name isn't specified, the sum of all processes managed is returned.

   Command line
          $ circusctl numprocesses [<name>]

   Options
       • <name>: name of the watcher

   Get the number of watchers
       Get the number of watchers in a arbiter

   ZMQ Message
          {
              "command": "numwatchers",
          }

       The response return the number of watchers in the 'numwatchers` property:

          { "status": "ok", "numwatchers": <n>, "time", "timestamp" }

   Command line
          $ circusctl numwatchers

   Get the value of all options for a watcher
       This command returns all option values for a given watcher.

   ZMQ Message
          {
              "command": "options",
              "properties": {
                  "name": "nameofwatcher",
              }
          }

       A message contains 1 property:

       • name: name of watcher

       The response object has a property options which is a dictionary of option names and values.

       eg:

          {
              "status": "ok",
              "options": {
                  "graceful_timeout": 300,
                  "send_hup": True,
                  ...
              },
              time': 1332202594.754644
          }

   Command line
          $ circusctl options <name>

   Options
       • <name>: name of the watcher

       Options Keys are:

       • numprocesses: integer, number of processes

       • warmup_delay: integer or number, delay to wait between process spawning in seconds

       • working_dir: string, directory where the process will be executed

       • uid: string or integer, user ID used to launch the process

       • gid: string or integer, group ID used to launch the process

       • send_hup: boolean, if TRU the signal HUP will be used on reload

       • shell: boolean, will run the command in the shell environment if true

       • cmd: string, The command line used to launch the process

       • env: object, define the environnement in which the process will be launch

       • retry_in: integer or number, time in seconds we wait before we retry  to  launch  the  process  if  the
         maximum number of attempts has been reach.

       • max_retry: integer, The maximum of retries loops

       • graceful_timeout: integer or number, time we wait before we definitely kill a process.

       • priority: used to sort watchers in the arbiter

       • singleton: if True, a singleton watcher.

       • max_age: time a process can live before being restarted

       • max_age_variance: variable additional time to live, avoids stampeding herd.

   Quit the arbiter immediately
       When the arbiter receive this command, the arbiter exit.

   ZMQ Message
          {
              "command": "quit",
              "waiting": False
          }

       The response return the status "ok".

       If  waiting  is  False  (default),  the  call  will  return immediately after calling stop_signal on each
       process.

       If waiting is True, the call will return only when the stop process is completely ended. Because  of  the
       graceful_timeout option, it can take some time.

   Command line
          $ circusctl quit [--waiting]

   Reload the arbiter or a watcher
       This command reloads all the process in a watcher or all watchers. This will happen in one of 3 ways:

       • If graceful is false, a simple restart occurs.

       • If send_hup is true for the watcher, a HUP signal is sent to each process.

       •

         Otherwise:

                • If  sequential  is false, the arbiter will attempt to spawn numprocesses new processes. If the
                  new processes are spawned successfully, the result is  that  all  of  the  old  processes  are
                  stopped, since by default the oldest processes are stopped when the actual number of processes
                  for a watcher is greater than numprocesses.

                • If sequential is true, the arbiter will restart each process  in  a  sequential  way  (with  a
                  warmup_delay pause between each step)

   ZMQ Message
          {
              "command": "reload",
              "properties": {
                  "name": '<name>",
                  "graceful": true,
                  "sequential": false,
                  "waiting": False
              }
          }

       The response return the status "ok". If the property graceful is set to true the processes will be exited
       gracefully.

       If the property name is present, then the reload will be applied to the watcher.

   Command line
          $ circusctl reload [<name>] [--terminate] [--waiting]
                                      [--sequential]

   Options
       • <name>: name of the watcher

       • --terminate; quit the node immediately

   Reload the configuration file
       This command reloads the configuration file, so changes in the configuration file will  be  reflected  in
       the configuration of circus.

   ZMQ Message
          {
              "command": "reloadconfig",
              "waiting": False
          }

       The response return the status "ok". If the property graceful is set to true the processes will be exited
       gracefully.

   Command line
          $ circusctl reloadconfig [--waiting]

   Restart the arbiter or a watcher
       This command restart all the process in a watcher or all watchers. This funtion  simply  stop  a  watcher
       then restart it.

   ZMQ Message
          {
              "command": "restart",
              "properties": {
                  "name": "<name>",
                  "waiting": False,
                  "match": "[simple|glob|regex]"
              }
          }

       The response return the status "ok".

       If the property name is present, then the reload will be applied to the watcher.

       If  waiting  is  False  (default),  the  call  will  return immediately after calling stop_signal on each
       process.

       If waiting is True, the call will return only when the restart process is completely  ended.  Because  of
       the graceful_timeout option, it can take some time.

       The match parameter can have the value simple for string compare, glob for wildcard matching (default) or
       regex for regex matching.

   Command line
          $ circusctl restart [name] [--waiting] [--match=simple|glob|regex]

   Options
       • <name>: name or pattern of the watcher(s)

       • <match>: watcher match method

   Remove a watcher
       This command removes a watcher dynamically from the arbiter.  The  watchers  are  gracefully  stopped  by
       default.

   ZMQ Message
          {
              "command": "rm",
              "properties": {
                  "name": "<nameofwatcher>",
                  "nostop": False,
                  "waiting": False
              }
          }

       The response return a status "ok".

       If  nostop  is  True  (default:  False),  the processes for the watcher will not be stopped - instead the
       watcher will just be forgotten by circus and the watcher  processes  will  be  responsible  for  stopping
       themselves.  If  nostop  is  not  specified  or  is  False,  then  the  watcher processes will be stopped
       gracefully.

       If waiting is False (default), the call will return immediately after starting to  remove  and  stop  the
       corresponding watcher.

       If  waiting  is  True,  the  call  will return only when the remove and stop process is completely ended.
       Because of the graceful_timeout option, it can take some time.

   Command line
          $ circusctl rm <name> [--waiting] [--nostop]

   Options
       • <name>: name of the watcher to remove

       • nostop: do not stop the watcher processes, just remove the watcher

   Set a watcher option
   ZMQ Message
          {
              "command": "set",
              "properties": {
                  "name": "nameofwatcher",
                  "options": {
                      "key1": "val1",
                      ..
                  }
                  "waiting": False
              }
          }

       The response return the status "ok". See the command Options for a list of key to set.

   Command line
          $ circusctl set <name> <key1> <value1> <key2> <value2> --waiting

   Send a signal
       This command allows you to send a signal to all processes in a watcher, a specific process in  a  watcher
       or its children.

   ZMQ Message
       To send a signal to all the processes for a watcher:

          {
              "command": "signal",
              "property": {
                  "name": <name>,
                  "signum": <signum>
          }

       To send a signal to a process:

          {
              "command": "signal",
              "property": {
                  "name": <name>,
                  "pid": <processid>,
                  "signum": <signum>
          }

       An  optional  property  "children"  can  be  used  to send the signal to all the children rather than the
       process itself:

          {
              "command": "signal",
              "property": {
                  "name": <name>,
                  "pid": <processid>,
                  "signum": <signum>,
                  "children": True
          }

       To send a signal to a process child:

          {
              "command": "signal",
              "property": {
                  "name": <name>,
                  "pid": <processid>,
                  "signum": <signum>,
                  "child_pid": <childpid>,
          }

       It is also possible to send a signal to all the children of the watcher:

          {
              "command": "signal",
              "property": {
                  "name": <name>,
                  "signum": <signum>,
                  "children": True
          }

       Lastly, you can send a signal to the process and its children, with the recursive option:

          {
              "command": "signal",
              "property": {
                  "name": <name>,
                  "signum": <signum>,
                  "recursive": True
          }

   Command line
          $ circusctl signal <name> [<pid>] [--children]
                  [--recursive] <signum>

   Options:
       • <name>: the name of the watcher

       • <pid>: integer, the process id.

       • <signum>: the signal number (or name) to send.

       • <childpid>: the pid of a child, if any

       • <children>: boolean, send the signal to all the children

       • <recursive>: boolean, send the signal to the process and its children

   Start the arbiter or a watcher
       This command starts all the processes in a watcher or all watchers.

   ZMQ Message
          {
              "command": "start",
              "properties": {
                  "name": '<name>",
                  "waiting": False,
                  "match": "[simple|glob|regex]"
              }
          }

       The response return the status "ok".

       If the property name is present, the watcher will be started.

       If waiting is False (default), the call will return immediately after calling start on each process.

       If waiting is True, the call will return only when the start process is completely ended. Because of  the
       graceful_timeout option, it can take some time.

       The match parameter can have the value simple for string compare, glob for wildcard matching (default) or
       regex for regex matching.

   Command line
          $ circusctl restart [name] [--waiting] [--match=simple|glob|regex]

   Options
       • <name>: name or pattern of the watcher(s)

       • <match>: watcher match method

   Get process infos
       You can get at any time some statistics about your processes with the stat command.

   ZMQ Message
       To get stats for all watchers:

          {
              "command": "stats"
          }

       To get stats for a watcher:

          {
              "command": "stats",
              "properties": {
                  "name": <name>
              }
          }

       To get stats for a process:

          {
              "command": "stats",
              "properties": {
                  "name": <name>,
                  "process": <processid>
              }
          }

       Stats can be extended with the extended_stats hook but extended stats need to be requested:

          {
              "command": "stats",
              "properties": {
                  "name": <name>,
                  "process": <processid>,
                  "extended": True
              }
          }

       The response retun an object per process with the property "info" containing some process informations:

          {
            "info": {
              "children": [],
              "cmdline": "python",
              "cpu": 0.1,
              "ctime": "0:00.41",
              "mem": 0.1,
              "mem_info1": "3M",
              "mem_info2": "2G",
              "nice": 0,
              "pid": 47864,
              "username": "root"
            },
            "process": 5,
            "status": "ok",
            "time": 1332265655.897085
          }

   Command Line
          $ circusctl stats [--extended] [<watchername>] [<processid>]

   Get the status of a watcher or all watchers
       This command start get the status of a watcher or all watchers.

   ZMQ Message
          {
              "command": "status",
              "properties": {
                  "name": '<name>",
              }
          }

       The response return the status "active" or "stopped" or the status / watchers.

   Command line
          $ circusctl status [<name>]

   Options
       • <name>: name of the watcher

   Example
          $ circusctl status dummy
          active
          $ circusctl status
          dummy: active
          dummy2: active
          refuge: active

   Stop watchers
       This command stops a given watcher or all watchers.

   ZMQ Message
          {
              "command": "stop",
              "properties": {
                  "name": "<name>",
                  "waiting": False,
                  "match": "[simple|glob|regex]"
              }
          }

       The response returns the status "ok".

       If the name property is present, then the stop will be applied to the watcher corresponding to that name.
       Otherwise, all watchers will get stopped.

       If waiting is False (default), the call will return immediatly after calling stop_signal on each process.

       If  waiting  is  True, the call will return only when the stop process is completly ended. Because of the
       graceful_timeout option, it can take some time.

       The match parameter can have the value simple for string compare, glob for wildcard matching (default) or
       regex for regex matching.

   Command line
          $ circusctl stop [name] [--waiting] [--match=simple|glob|regex]

   Options
       • <name>: name or pattern of the watcher(s)

       • <match>: watcher match method

   CLI tools
   circus-top
       circus-top  is  a  top-like console you can run to watch live your running Circus system. It will display
       the CPU, Memory usage and socket hits if you have some.

       Example of output:

          -----------------------------------------------------------------------
          circusd-stats
           PID                 CPU (%)             MEMORY (%)
          14252                 0.8                 0.4
                                0.8 (avg)           0.4 (sum)

          dummy
           PID                 CPU (%)             MEMORY (%)
          14257                 78.6                0.1
          14256                 76.6                0.1
          14258                 74.3                0.1
          14260                 71.4                0.1
          14259                 70.7                0.1
                                74.32 (avg)         0.5 (sum)

          ----------------------------------------------------------------------

       circus-top is a read-only console. If you want to interact with the system, use circusctl.

   circusctl
       circusctl can be used to run any command listed in commands . For example, you can get a list of all  the
       watchers, you can do

          $ circusctl list

       Besides  supporting a handful of options you can also specify the endpoint circusctl should use using the
       CIRCUSCTL_ENDPOINT environment variable.

   The Web Console
       Circus comes with a Web Console that can be used to manage the system.

       The Web Console lets you:

       • Connect to any running Circus system

       • Watch the processes CPU and Memory usage in real-time

       • Add or kill processes

       • Add new watchers

       NOTE:
          The real-time CPU & Memory usage feature uses the stats socket.  If you want to activate it, make sure
          the Circus system you'll connect to has the stats enpoint enabled in its configuration:

              [circus]
              statsd = True

          By default, this option is not activated.

       The web console is its own package, you need to install:

          $ pip install circus-web

       To enable the console, add a few options in the Circus ini file:

          [circus]
          httpd = True
          httpd_host = localhost
          httpd_port = 8080

       httpd_host and httpd_port are optional, and default to localhost and 8080.

       If you want to run the web app on its own, just run the circushttpd script:

          $ circushttpd
          Bottle server starting up...
          Listening on http://localhost:8080/
          Hit Ctrl-C to quit.

       By  default the script will run the Web Console on port 8080, but the --port option can be used to change
       it.

   Using the console
       Once the script is running, you can open a browser and visit http://localhost:8080.  You should get  this
       screen: [image]

       The Web Console is ready to be connected to a Circus system, given its endpoint.  By default the endpoint
       is tcp://127.0.0.1:5555.

       Once you hit Connect, the web application will connect to the Circus system.

       With the Web Console logged in, you should get a list of watchers, and a  real-time  status  of  the  two
       Circus processes (circusd and circusd-stats).

       You  can  click  on  the  status of each watcher to toggle it from Active (green) to Inactive (red). This
       change is effective immediatly and let you start & stop watchers.

       If you click on the watcher name, you will  get  a  web  page  for  that  particular  watcher,  with  its
       processes:

       On this screen, you can add or remove processes, and kill existing ones.

       Last but not least, you can add a brand new watcher by clicking on the Add Watcher link in the left menu:
       .SS Running behind Nginx

       Nginx can act as a proxy and security layer in front of circus-web.

       NOTE:
          To receive real-time status updates and graphs in circus-web, you must provide a Nginx proxy  solution
          that has websocket support

   Nginx >= 1.3.13
       As  of  Nginx>=1.3.13 websocket support is built-in, so there is no need to combine Nginx with Varnish or
       HAProxy.  An example Nginx config with websocket support:

          upstream circusweb_server {
            server 127.0.0.1:8080;
          }

          server {
           listen   80;
           server_name  _;

           location / {
             proxy_pass http://circusweb_server;
             proxy_http_version 1.1;
             proxy_set_header Upgrade $http_upgrade;
             proxy_set_header Connection "upgrade";
             proxy_set_header Host $host;
             proxy_set_header X-Real-IP $remote_addr;
             proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
             proxy_set_header X-Forwarded-Proto http;
             proxy_redirect off;
            }

           location ~/media/\*(.png|.jpg|.css|.js|.ico)$ {
             alias /path_to_site-packages/circusweb/media/;
            }
          }

   Nginx < 1.3.13
       Nginx versions < 1.3.13 do not have websocket support built-in.

       To provide websocket support for circus-web when using Nginx < 1.3.13, you can combine Nginx with Varnish
       or HAProxy. That is, Nginx in front of circus-web, with Varnish or HAProxy in front of Nginx.

       The  example  below  shows the combined Nginix and Varnish configuration required to proxy circus-web and
       provide websocket support.

       Nginx configuration:

          upstream circusweb_server {
            server 127.0.0.1:8080;
          }

          server {
           listen   8001;
           server_name  _;

           location / {
              proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
              proxy_set_header Host $http_host;
              proxy_redirect off;
              proxy_pass http://circusweb_server;
            }

           location ~/media/\*(.png|.jpg|.css|.js|.ico)$ {
             alias /path_to_site-packages/circusweb/media/;
            }
          }

       If you want more Nginx configuration options, see http://wiki.nginx.org/HttpProxyModule.

       Varnish configuration:

          backend default {
              .host = "127.0.0.1";
              .port = "8001";
          }

          backend socket {
              .host = "127.0.0.1";
              .port = "8080";
              .connect_timeout = 1s;
              .first_byte_timeout = 2s;
              .between_bytes_timeout = 60s;
          }

          sub vcl_pipe {
               if (req.http.upgrade) {
                   set bereq.http.upgrade = req.http.upgrade;
               }
          }

          sub vcl_recv {
              if (req.http.Upgrade ~ "(?i)websocket") {
                  set req.backend = socket;
                return (pipe);
              }
          }

       In the Varnish configuration example above two backends are defined.  One serving the web console and one
       serving  the  socket  connections.   Web  console  requests  are  bound  to port 8001. The Nginx 'server'
       directive should be configured to listen on port 8001.

       Websocket connections are upgraded and piped directly to the circushttpd process listening on  port  8080
       by Varnish. i.e. bypassing the Nginx proxy.

   Ubuntu
       Since  the  version  13.10 (Saucy), Ubuntu includes Nginx with websocket support in its own repositories.
       For older versions, you can install Nginx>=1.3.13 from the official Nginx stable PPA, as so:

          sudo apt-get install python-software-properties
          sudo add-apt-repository ppa:nginx/stable
          sudo apt-get update
          sudo apt-get install nginx
          nginx -v

   Password-protect circushttpd
       As explained in the Security page, running circushttpd is pretty unsafe. We don't provide any security in
       Circus    itself,    but    you   can   protect   your   console   at   the   NGinx   level,   by   using
       http://wiki.nginx.org/HttpAuthBasicModule

       Example:

          location / {
              proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
              proxy_set_header Host $http_host;
              proxy_set_header X-Forwarded-Host: $http_host;
              proxy_set_header X-Forwarded-Proto: $scheme;
              proxy_redirect off;
              proxy_pass http://127.0.0.1:8080;
              auth_basic            "Restricted";
              auth_basic_user_file  /path/to/htpasswd;
          }

       The htpasswd file contains users and their passwords, and a password prompt will pop when you access  the
       console.

       You   can   use   Apache's   htpasswd  script  to  edit  it,  or  the  Python  script  they  provide  at:
       http://trac.edgewall.org/browser/trunk/contrib/htpasswd.py

       However, there's no native support for the combined use of HTTP Authentication and WebSockets (the server
       will  throw  HTTP  401  error  codes).  A  workaround is to disable such authentication for the socket.io
       server.

       Example (needs to be added before the previous rule):

          location /socket.io {
              proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
              proxy_set_header Host $http_host;
              proxy_set_header X-Forwarded-Host: $http_host;
              proxy_set_header X-Forwarded-Proto: $scheme;
              proxy_redirect off;
              proxy_pass http://127.0.0.1:8080;
          }

       Of course that's just one way to protect your web console, you could use many other techniques.

   Extending the web console
       We picked bottle to build the webconsole, mainly because it's a really tiny  framework  that  doesn't  do
       much. By having a look at the code of the web console, you'll eventually find out that it's really simple
       to understand.

       Here is how it's split:

       • The circushttpd.py file contains the "views" definitions and some code to handle the socket  connection
         (via socketio).

       • the controller.py contains a single class which is in charge of doing the communication with the circus
         controller. It allows to have a nicer high level API when defining the web server.

       If you want to add a feature in the web console you can reuse the code that's existing. A few  tools  are
       at your disposal to ease the process:

       • There  is  a  render_template function, which takes the named arguments you pass to it and pass them to
         the template renderer and return the resulting HTML. It also passes some additional variables, such  as
         the session, the circus version and the client if defined.

       • If you want to run commands and doa redirection depending the result of it, you can use the run_command
         function, which takes a callable as a first argument, a message in case of success  and  a  redirection
         url.

       The  StatsNamespace class is responsible for managing the websocket communication on the server side. Its
       documentation should help you to understand what it does.

   Working with sockets
       Circus can bind network sockets and manage them as it does for processes.

       The main idea is that a child process that's created by Circus to run one of the  watcher's  command  can
       inherit from all the opened file descriptors.

       That's how Apache or Unicorn works, and many other tools out there.

   Goal
       The  goal  of  having  sockets  managed  by Circus is to be able to manage network applications in Circus
       exactly like other applications.

       For example, if you use Circus with Chaussette -- a WGSI server, you can  get  a  very  fast  web  server
       running and manage "Web Workers" in Circus as you would do for any other process.

       Splitting the socket managment from the network application itself offers a lot of opportunities to scale
       and manage your stack.

   Design
       The gist of the feature is done by binding the socket and start listening to it in circusd:

          import socket

          sock = socket.socket(FAMILY, TYPE)
          sock.bind((HOST, PORT))
          sock.listen(BACKLOG)
          fd = sock.fileno()

       Circus then keeps track of all the opened fds, and let the processes it runs as children have  access  to
       them if they want.

       If you create a small Python network script that you intend to run in Circus, it could look like this:

          import socket
          import sys

          fd = int(sys.argv[1])   # getting the FD from circus
          sock = socket.fromfd(fd, FAMILY, TYPE)

          # dealing with one request at a time
          while True:
              conn, addr = sock.accept()
              request = conn.recv(1024)
              .. do something ..
              conn.sendall(response)
              conn.close()

       Then Circus could run like this:

          [circus]
          check_delay = 5
          endpoint = tcp://127.0.0.1:5555
          pubsub_endpoint = tcp://127.0.0.1:5556
          stats_endpoint = tcp://127.0.0.1:5557

          [watcher:dummy]
          cmd = mycoolscript $(circus.sockets.foo)
          use_sockets = True
          warmup_delay = 0
          numprocesses = 5

          [socket:foo]
          host = 127.0.0.1
          port = 8888

       $(circus.sockets.foo)  will  be replaced by the FD value once the socket is created and bound on the 8888
       port.

       NOTE:
          Starting at Circus 0.8 there's an alternate syntax to avoid some conflicts with some  config  parsers.
          You can write:

              ((circus.sockets.foo))

   Real-world example
       Chaussette is the perfect Circus companion if you want to run your WSGI application.

       Once  it's  installed,  running  5  meinheld  workers  can  be  done by creating a socket and calling the
       chaussette command in a worker, like this:

          [circus]
          endpoint = tcp://127.0.0.1:5555
          pubsub_endpoint = tcp://127.0.0.1:5556
          stats_endpoint = tcp://127.0.0.1:5557

          [watcher:web]
          cmd = chaussette --fd $(circus.sockets.web) --backend meinheld mycool.app
          use_sockets = True
          numprocesses = 5

          [socket:web]
          host = 0.0.0.0
          port = 8000

       We did not publish benchmarks yet, but a Web cluster managed by Circus with a Gevent or Meinheld  backend
       is as fast as any pre-fork WSGI server out there.

   Using built-in plugins
       Circus  comes  with  a  few built-in plugins. This section presents these plugins and their configuration
       options.

   Statsd
          use    set to 'circus.plugins.statsd.StatsdEmitter'

          application_name
                 the name used to identify the bucket prefix to emit the stats to  (it  will  be  prefixed  with
                 circus. and suffixed with .watcher)

          host   the host to post the statds data to

          port   the port the statsd daemon listens on

          sample_rate
                 if you prefer a different sample rate than 1, you can set it here

   FullStats
          An  extension  on the Statsd plugin that is also publishing the process stats. As such it has the same
          configuration options as Statsd and the following.

          use    set to circus.plugins.statsd.FullStats

          loop_rate
                 the frequency the plugin should ask for the stats in seconds. Default: 60.

   RedisObserver
          This services observers a redis process for you, publishes the information to  statsd  and  offers  to
          restart the watcher when it doesn't react in a given timeout. This plugin requires redis-py  to run.

          It has the same configuration as statsd and adds the following:

          use    set to   circus.plugins.redis_observer.RedisObserver

          loop_rate
                 the frequency the plugin should ask for the stats in seconds. Default: 60.

          redis_url
                 the database to check for as a redis url. Default: "redis://localhost:6379/0"

          timeout
                 the timeout in seconds the request can take before it is considered down. Defaults to 5.

          restart_on_timeout
                 the  name  of  the process to restart when the request timed out. No restart triggered when not
                 given. Default: None.

   HttpObserver
          This services observers a http process for you by pinging a certain website regularly. Similar to  the
          redis observer it offers to restart the watcher on an error. It requires tornado to run.

          It has the same configuration as statsd and adds the following:

          use    set to circus.plugins.http_observer.HttpObserver

          loop_rate
                 the frequency the plugin should ask for the stats in seconds. Default: 60.

          check_url
                 the url to check for. Default: http://localhost/

          timeout
                 the timeout in seconds the request can take before it is considered down. Defaults to 10.

          restart_on_error
                 the  name  of  the  process to restart when the request timed out or returned any other kind of
                 error. No restart triggered when not given. Default: None.

   ResourceWatcher
          This services watches the resources of the given process and  triggers  a  restart  when  they  exceed
          certain limitations too often in a row.

          It has the same configuration as statsd and adds the following:

          use    set to circus.plugins.resource_watcher.ResourceWatcher

          loop_rate
                 the frequency the plugin should ask for the stats in seconds. Default: 60.

          watcher
                 the  watcher  this  resource  watcher  should be looking after.  (previously called service but
                 service is now deprecated)

          max_cpu
                 The maximum cpu one process is allowed to consume (in %). Default: 90

          min_cpu
                 The minimum cpu one process should consume (in %). Default: None (no minimum) You can  set  the
                 min_cpu  to  0  (zero),  in this case if one process consume exactly 0% cpu, it will trigger an
                 exceeded limit.

          max_mem
                 The amount of memory one process of this watcher is allowed to consume.  Default:  90.   If  no
                 unit  is  specified,  the  value  is  in %. Example: 50 If a unit is specified, the value is in
                 bytes. Supported units are B, K, M, G, T, P, E, Z, Y. Example: 250M

          min_mem
                 The minimum memory one process of this watcher should consume. Default: None (no minimum).   If
                 no  unit  is  specified, the value is in %. Example: 50 If a unit is specified, the value is in
                 bytes. Supported units are B, K, M, G, T, P, E, Z, Y. Example: 250M

          health_threshold
                 The health is the average of cpu and memory (in  %)  the  watchers  processes  are  allowed  to
                 consume (in %). Default: 75

          max_count
                 How  often  these  limits  (each one is counted separately) are allowed to be exceeded before a
                 restart will be triggered. Default: 3

       Example:

          [circus]
          ; ...

          [watcher:program]
          cmd = sleep 120

          [plugin:myplugin]
          use = circus.plugins.resource_watcher.ResourceWatcher
          watcher = program
          min_cpu = 10
          max_cpu = 70
          min_mem = 0
          max_mem = 20

   Watchdog
          Plugin that binds an udp socket and wait for  watchdog  messages.   For  "watchdoged"  processes,  the
          watchdog  will  kill  them  if they don't send a heartbeat in a certain period of time materialized by
          loop_rate * max_count. (circus will automatically restart the missing processes in the watcher)

          Each monitored process should send udp message at least at the loop_rate.  The udp message format is a
          line  of text, decoded using msg_regex parameter.  The heartbeat message MUST at least contain the pid
          of the process sending the message.

          The list of monitored watchers are determined by the parameter watchers_regex in the configuration.

          Configuration parameters:

          use    set to circus.plugins.watchdog.WatchDog

          loop_rate
                 watchdog loop rate in seconds. At each loop, WatchDog will looks for "dead" processes.

          watchers_regex
                 regex for matching watcher names that should be monitored by  the  watchdog  (default:  .*  all
                 watchers are monitored)

          msg_regex
                 regex     for     decoding    the    received    heartbeat    message    in    udp    (default:
                 ^(?P<pid>.*);(?P<timestamp>.*)$) the default format is a simple text message: pid;timestamp

          max_count
                 max number of passed loop without receiving any heartbeat before restarting  process  (default:
                 3)

          ip     ip the watchdog will bind on (default: 127.0.0.1)

          port   port the watchdog will bind on (default: 1664)

   Flapping
          When  a  worker  restarts  too  often,  we say that it is flapping.  This plugin keeps track of worker
          restarts and stops the corresponding watcher in case it is  flapping.  This  plugin  may  be  used  to
          automatically stop workers that get constantly restarted because they're not working properly.

          use    set to circus.plugins.flapping.Flapping

          attempts
                 the  number  of  times  a  process  can  restart,  within window seconds, before we consider it
                 flapping (default: 2)

          window the time window in seconds to test for flapping.  If the process restarts  more  than  attempts
                 times within this time window, we consider it a flapping process.  (default: 1)

          retry_in
                 time in seconds to wait until we try to start again a process that has been flapping. (default:
                 7)

          max_retry
                 the number of times we attempt to start a process that has been flapping, before we abandon and
                 stop the whole watcher. (default: 5) Set to -1 to disable max_retry and retry indefinitely.

          active define if the plugin is active or not (default: True).  If the global flag is set to False, the
                 plugin is not started.

       Options can be overriden in the watcher section using a flapping.  prefix. For instance, here is how  you
       would configure a specific max_retry value for nginx:

          [watcher:nginx]
          cmd = /path/to/nginx
          flapping.max_retry = 2

          [watcher:myscript]
          cmd = ./my_script.py

          ; ... other watchers

          [plugin:flapping]
          use = circus.plugins.flapping.Flapping
          max_retry = 5

   CommandReloader
          This  plugin  will  restart  watchers  when  their  command file is modified. It works by checking the
          modification time and the path of the file pointed by the cmd option every loop_rate seconds. This may
          be useful while developing worker processes or even for hot code upgrade in production.

          use    set to circus.plugins.command_reloader.CommandReloader

          loop_rate
                 the frequency the plugin should check for modification in seconds. Default: 1.

   Deployment
       Although the Circus daemon can be managed with the circusd command, it's easier to have it start on boot.
       If your system supports Upstart, you can create this Upstart script in /etc/init/circus.conf.

          start on filesystem and net-device-up IFACE=lo
          stop on runlevel [016]

          respawn
          exec /usr/local/bin/circusd /etc/circus/circusd.ini

       This assumes that circusd.ini is located at /etc/circus/circusd.ini. After  rebooting,  you  can  control
       circusd with the service command:

          # service circus start/stop/restart

       If    your    system    supports    systemd,    you   can   create   this   systemd   unit   file   under
       /etc/systemd/system/circus.service.

          [Unit]
          Description=Circus process manager
          After=syslog.target network.target nss-lookup.target

          [Service]
          Type=simple
          ExecReload=/usr/bin/circusctl reload
          ExecStart=/usr/bin/circusd /etc/circus/circus.ini
          Restart=always
          RestartSec=5

          [Install]
          WantedBy=default.target

       A reboot isn't required if you run the daemon-reload command below:

          # systemctl --system daemon-reload

       Then circus can be managed via:

          # systemctl start/stop/status/reload circus

   Recipes
       This section will contain recipes to deploy Circus. Until then you can look at Pete's Puppet recipe or at
       Remy's Chef recipe

   Papa Process Kernel
       One  problem common to process managers is that you cannot restart the process manager without restarting
       all of the processes it manages. This makes it difficult to  deploy  a  new  version  of  Circus  or  new
       versions of any of the libraries on which it depends.

       If  you are on a Unix-type system, Circus can use the Papa process kernel.  When used, Papa will create a
       long-lived daemon that will serve as the host for any processes and sockets you create with it. If circus
       is shutdown, Papa will maintain everything it is hosting.

   Setup
       Start by installing the papa and setproctitle modules:

          pip install papa
          pip install setproctitle

       The  setproctitle module is optional. It will be used if present to rename the Papa daemon for top and ps
       to something like "papa daemon from circusd".  If you do not install the setproctitle module, that  title
       will be the command line of the process that launched it. Very confusing.

       Once  Papa  is installed, add use_papa=true to your critical processes and sockets. Generally you want to
       house all of the processes of your stack in Papa, and none of the Circus support processes  such  as  the
       flapping and stats plugins.

          [circus]
          loglevel = info

          [watcher:nginx]
          cmd = /usr/local/nginx/sbin/nginx -p /Users/scottmax/Source/service-framework/Common/conf/nginx -c /Users/scottmax/Source/service-framework/Common/conf/nginx/nginx.conf
          warmup_delay = 3
          graceful_timeout = 10
          max_retry = 5
          singleton = true
          send_hup = true
          stop_signal = QUIT
          stdout_stream.class = FileStream
          stdout_stream.filename = /var/logs/web-server.log
          stdout_stream.max_bytes = 10000000
          stdout_stream.backup_count = 10
          stderr_stream.class = FileStream
          stderr_stream.filename = /var/logs/web-server-error.log
          stderr_stream.max_bytes = 1000000
          stderr_stream.backup_count = 10
          active = true
          use_papa = true

          [watcher:logger]
          cmd = /my_service/env/bin/python logger.py run
          working_dir = /my_service
          graceful_timeout = 10
          singleton = true
          stop_signal = INT
          stdout_stream.class = FileStream
          stdout_stream.filename = /var/logs/logger.log
          stdout_stream.max_bytes = 10000000
          stdout_stream.backup_count = 10
          stderr_stream.class = FileStream
          stderr_stream.filename = /var/logs/logger.log
          stderr_stream.max_bytes = 1000000
          stderr_stream.backup_count = 10
          priority = 50
          use_papa = true

          [watcher:web_app]
          cmd = /my_service/env/bin/uwsgi --ini uwsgi-live.ini --socket fd://$(circus.sockets.web) --stats 127.0.0.1:809$(circus.wid)
          working_dir = /my_service/web_app
          graceful_timeout=10
          stop_signal = QUIT
          use_sockets = True
          stdout_stream.class = FileStream
          stdout_stream.filename = /var/logs/web_app.log
          stdout_stream.max_bytes = 10000000
          stdout_stream.backup_count = 10
          stderr_stream.class = FileStream
          stderr_stream.filename = /var/logs/web_app.log
          stderr_stream.max_bytes = 1000000
          stderr_stream.backup_count = 10
          hooks.after_spawn = examples.uwsgi_lossless_reload.children_started
          hooks.before_signal = examples.uwsgi_lossless_reload.clean_stop
          hooks.extended_stats = examples.uwsgi_lossless_reload.extended_stats
          priority = 40
          use_papa = true

          [socket:web]
          path = /my_service/sock/uwsgi
          use_papa = true

          [plugin:flapping]
          use = circus.plugins.flapping.Flapping
          window = 10
          priority = 1000

       NOTE:
          If the Papa processes use any sockets, those sockets must also use papa.

   Design Goal
       Papa is designed to be very minimalist in features and requirements. It does:

       • Start and stop sockets

       • Provide a key/value store

       • Start processes and return stdout, stderr and the exit code

       It does not:

       • Restart processes

       • Provide a way to stop processes

       • Provide any information about processes other than whether or not they are still running

       Papa requires no third-party libraries so it can run on just the standard Python library. It can make use
       of the setproctitle package but that is only used for making the title prettier for ps and top and is not
       essential.

       The functionality has been kept to a minimum so that you should never need to restart the Papa daemon. As
       much of the functionality has been pushed to the client library as possible. That way you should be  able
       to deploy a new copy of Papa for new client features without needing to restart the Papa daemon.  Papa is
       meant to be a pillar of stability in a changing sea of 3rd party libraries.

   Operation
       Most things remain unchanged whether you use Papa or not. You can still start and stop processes. You can
       still get status and stats for processes. The main thing that changes is that when you do circusctl quit,
       all of the Papa processes are left  running.  When  you  start  circusd  back  up,  those  processes  are
       recovered.

       NOTE:
          When processes are recovered, before_start and before_spawn hooks are skipped.

   Logging
       While Circus is shut down, Papa will store up to 2M of output per process. Then it will start dumping the
       oldest data. When you restart Circus, this cached output will be quickly retrieved and sent to the output
       streams. Papa requires that receipt of output be acknowledged, so you should not lose any output during a
       shutdown.

       Not only that, but Papa saves the timestamp of the output. Circus has been enhanced to take advantage  of
       timestamp  data  if  present. So if you are writing the output to log files or somewhere, your timestamps
       should all be correct.

   Problems
       If you use the incr or decr command to change the process count for a watcher, this will be reset to  the
       level specified in the INI file when circusd is restarted.

       Also,  I have experienced problems with the combination of copy_env and virtualenv. You may note that the
       INI sample above circumvents this issue with explicit paths.

   Telnet Interface
       Papa has a basic command-line interface that you can access through telnet:

          telnet localhost 20202
          help

   Circus for developers
   Using Circus as a library
       Circus provides high-level classes and  functions  that  will  let  you  manage  processes  in  your  own
       applications.

       For example, if you want to run four processes forever, you could write:

          from circus import get_arbiter

          myprogram = {"cmd": "python myprogram.py", "numprocesses": 4}

          arbiter = get_arbiter([myprogram])
          try:
              arbiter.start()
          finally:
              arbiter.stop()

       This  snippet  will  run  four instances of myprogram and watch them for you, restarting them if they die
       unexpectedly.

       To learn more about this, see library

   Extending Circus
       It's easy to extend Circus to create a more complex system, by listening to all the  circusd  events  via
       its pub/sub channel, and driving it via commands.

       That's  how  the flapping feature works for instance: it listens to all the processes dying, measures how
       often it happens, and stops the incriminated watchers after too many restarts attempts.

       Circus comes with a plugin system to help you write such extensions, and a few built-in plugins  you  can
       reuse. See plugins.

       You  can  also  have a more subtile startup and shutdown behavior by using the hooks system that will let
       you run arbitrary code before and after some processes are started or stopped. See hooks.

       Last but not least, you can also add new commands. See addingcmds.

   Developers Documentation Index
   Circus Library
       The Circus package is composed of a high-level get_arbiter() function and many classes.  In  most  cases,
       using  the  high-level  function  should be enough, as it creates everything that is needed for Circus to
       run.

       You can subclass Circus' classes if you need more granularity than what is offered by the configuration.

   The get_arbiter function
       get_arbiter() is just a convenience on top of the various circus classes. It  creates  a  arbiter  (class
       Arbiter) instance with the provided options, which in turn runs a single Watcher with a single Process.

       circus.get_arbiter()

       Example:

          from circus import get_arbiter

          arbiter = get_arbiter([{"cmd": "myprogram", "numprocesses": 3}])
          try:
              arbiter.start()
          finally:
              arbiter.stop()

   Classes
       Circus provides a series of classes you can use to implement your own process manager:

       • Process: wraps a running process and provides a few helpers on top of it.

       • Watcher:  run  several  instances  of  Process  against  the same command. Manage the death and life of
         processes.

       • Arbiter: manages several Watcher.

       class  circus.process.Process(name,  wid,  cmd,  args=None,  working_dir=None,   shell=False,   uid=None,
       gid=None,    env=None,    rlimits=None,   executable=None,   use_fds=False,   watcher=None,   spawn=True,
       pipe_stdout=True, pipe_stderr=True, close_child_stdout=False, close_child_stderr=False)
              Wraps a process.

              Options:

              • wid: the process unique identifier. This value will be used to replace the $WID  string  in  the
                command line if present.

              • cmd:  the  command  to  run. May contain any of the variables available that are being passed to
                this class. They will be replaced using the python format syntax.

              • args: the arguments for the command to run. Can be a list or a string. If  args  is   a  string,
                it's splitted using shlex.split(). Defaults to None.

              • executable:  When  executable is given, the first item in the args sequence obtained from cmd is
                still treated by most programs as the command name, which can then be different from the  actual
                executable name. It becomes the display name for the executing program in utilities such as ps.

              • working_dir:  the  working directory to run the command in. If not provided, will default to the
                current working directory.

              • shell: if True, will run the command in the shell environment. False by default.  warning:  this
                is a security hazard.

              • uid:  if  given,  is  the  user  id  or name the command should run with. The current uid is the
                default.

              • gid: if given, is the group id or name the command should run  with.  The  current  gid  is  the
                default.

              • env: a mapping containing the environment variables the command will run with. Optional.

              • rlimits: a mapping containing rlimit names and values that will be set before the command runs.

              • use_fds: if True, will not close the fds in the subprocess. Must be be set to True on Windows if
                stdout or stderr are redirected.  default: False.

              • pipe_stdout: if True, will open a PIPE on stdout. default: True.

              • pipe_stderr: if True, will open a PIPE on stderr. default: True.

              • close_child_stdout: If True, redirects the child process' stdout to /dev/null  after  the  fork.
                default: False.

              • close_child_stderr:  If  True,  redirects the child process' stdout to /dev/null after the fork.
                default: False.

              age()  Return the age of the process in seconds.

              children()
                     Return a list of children pids.

              info() Return process info.

                     The info returned is a mapping with these keys:

                     • mem_info1: Resident Set Size Memory in bytes (RSS)

                     • mem_info2: Virtual Memory Size in bytes (VMS).

                     • cpu: % of cpu usage.

                     • mem: % of memory usage.

                     • ctime: process CPU (user + system) time in seconds.

                     • pid: process id.

                     • username: user name that owns the process.

                     • nice: process niceness (between -20 and 20)

                     • cmdline: the command line the process was run with.

              is_child(pid)
                     Return True is the given pid is a child of that process.

              pid    Return the pid

              send_signal(*args, **kw)
                     Sends a signal sig to the process.

              send_signal_child(*args, **kw)
                     Send signal signum to child pid.

              send_signal_children(*args, **kw)
                     Send signal signum to all children.

              status Return the process status as a constant

                     • RUNNING

                     • DEAD_OR_ZOMBIE

                     • UNEXISTING

                     • OTHER

              stderr Return the stdout stream

              stdout Return the stdout stream

              stop(*args, **kw)
                     Stop the process and close stdout/stderr

                     If the corresponding process is still here (normally it's already killed by the watcher), a
                     SIGTERM is sent, then a SIGKILL after 1 second.

                     The  shutdown  process  (SIGTERM  then SIGKILL) is normally taken by the watcher. So if the
                     process is still there here, it's a kind of bad behavior because the graceful timeout won't
                     be respected here.

       Example:

          >>> from circus.process import Process
          >>> process = Process('Top', 'top', shell=True)
          >>> process.age()
          3.0107998847961426
          >>> process.info()
          'Top: 6812  N/A tarek Zombie N/A N/A N/A N/A N/A'
          >>> process.status
          1
          >>> process.stop()
          >>> process.status
          2
          >>> process.info()
          'No such process (stopped?)'

       class  circus.watcher.Watcher(name,  cmd,  args=None, numprocesses=1, warmup_delay=0.0, working_dir=None,
       shell=False,  shell_args=None,   uid=None,   max_retry=5,   gid=None,   send_hup=False,   stop_signal=15,
       stop_children=False,  env=None,  graceful_timeout=30.0, prereload_fn=None, rlimits=None, executable=None,
       stdout_stream=None,  stderr_stream=None,  priority=0,  loop=None,   singleton=False,   use_sockets=False,
       copy_env=False,    copy_path=False,    max_age=0,    max_age_variance=30,    hooks=None,    respawn=True,
       autostart=True,  on_demand=False,  virtualenv=None,  close_child_stdout=False,  close_child_stderr=False,
       virtualenv_py_ver=None, use_papa=False, **options)
              Class managing a list of processes for a given command.

              Options:

              • name: name given to the watcher. Used to uniquely identify it.

              • cmd: the command to run. May contain $WID, which will be replaced by wid.

              • args:  the  arguments  for  the command to run. Can be a list or a string. If args is  a string,
                it's splitted using shlex.split(). Defaults to None.

              • numprocesses: Number of processes to run.

              • working_dir: the working directory to run the command in. If not provided, will default  to  the
                current working directory.

              • shell:  if  True, will run the command in the shell environment. False by default. warning: this
                is a security hazard.

              • uid: if given, is the user id or name the command should  run  with.  The  current  uid  is  the
                default.

              • gid:  if  given,  is  the  group  id or name the command should run with. The current gid is the
                default.

              • send_hup: if True, a process reload will be done by  sending  the  SIGHUP  signal.  Defaults  to
                False.

              • stop_signal: the signal to send when stopping the process.  Defaults to SIGTERM.

              • stop_children: send the stop_signal to the children too.  Defaults to False.

              • env: a mapping containing the environment variables the command will run with. Optional.

              • rlimits: a mapping containing rlimit names and values that will be set before the command runs.

              • stdout_stream: a mapping that defines the stream for the process stdout. Defaults to None.

                Optional. When provided, stdout_stream is a mapping containing up to three keys:

                • class: the stream class. Defaults to circus.stream.FileStreamfilename: the filename, if using a FileStream

                • max_bytes:  maximum  file  size,  after which a new output file is opened. defaults to 0 which
                  means no maximum size (only applicable with FileStream).

                • backup_count: how many backups to retain  when  rotating  files  according  to  the  max_bytes
                  parameter. defaults to 0 which means no backups are made (only applicable with FileStream)

                This  mapping  will  be  used  to  create  a stream callable of the specified class.  Each entry
                received by the callable is a mapping containing:

                • pid - the process pid

                • name - the stream name (stderr or stdout)

                • data - the data

                This is not supported on Windows.

              • stderr_stream: a mapping that defines the stream for the process stderr. Defaults to None.

                Optional. When provided, stderr_stream is a mapping containing up to three keys:  -  class:  the
                stream  class.  Defaults  to  circus.stream.FileStream  -  filename:  the  filename,  if using a
                FileStream - max_bytes: maximum file size, after which a new output file is
                   opened. defaults to 0 which means no maximum size (only applicable with FileStream)

                • backup_count: how many backups to retain  when  rotating  files  according  to  the  max_bytes
                  parameter. defaults to 0 which means no backups are made (only applicable with FileStream).

                This mapping will be used to create a stream callable of the specified class.

                Each entry received by the callable is a mapping containing:

                • pid - the process pid

                • name - the stream name (stderr or stdout)

                • data - the data

                This is not supported on Windows.

              • priority -- integer that defines a priority for the watcher. When the Arbiter do some operations
                on all watchers, it will sort them with this field, from the  bigger  number  to  the  smallest.
                (default: 0)

              • singleton -- If True, this watcher has a single process.  (default:False)

              • use_sockets  --  If  True,  the  processes will inherit the file descriptors, thus can reuse the
                sockets opened by circusd.  (default: False)

              • on_demand -- If True, the processes will be started only at the first connection to  the  socket
                (default: False)

              • copy_env  --  If True, the environment in which circus is running run will be reproduced for the
                workers. This defaults to True  on  Windows  as  you  cannot  run  any  executable  without  the
                SYSTEMROOT variable. (default: False)

              • copy_path  --  If  True,  circusd  sys.path  is sent to the process through PYTHONPATH. You must
                activate copy_env for copy_path to work. (default: False)

              • max_age: If set after around max_age seconds, the process is replaced with a new one.  (default:
                0, Disabled)

              • max_age_variance:  The  maximum number of seconds that can be added to max_age. This extra value
                is to avoid restarting all processes at the same time.  A process will live between max_age  and
                max_age + max_age_variance seconds.

              • hooks:  callback functions for hooking into the watcher startup and shutdown process. hooks is a
                dict where each key is the hook name and each value is a 2-tuple with the name of  the  callable
                or  the  callabled  itself  and  a  boolean flag indicating if an exception occuring in the hook
                should  not  be  ignored.   Possible  values  for  the  hook  name:  before_start,  after_start,
                before_spawn,    after_spawn,   before_stop,   after_stop.,   before_signal,   after_signal   or
                extended_stats.

              • options -- extra options for the worker.  All  options  found  in  the  configuration  file  for
                instance,  are  passed  in  this  mapping  --  this  can be used by plugins for watcher-specific
                options.

              • respawn -- If set  to  False,  the  processes  handled  by  a  watcher  will  not  be  respawned
                automatically. (default: True)

              • virtualenv  --  The  root  directory  of  a  virtualenv.  If provided, the watcher will load the
                environment for its execution. (default: None)

              • close_child_stdout: If True, closes the stdout after the fork.  default: False.

              • close_child_stderr: If True, closes the stderr after the fork.  default: False.

              • use_papa: If True, use the papa process kernel for this process.  default: False.

              kill_process(*args, **kwargs)
                     Kill process (stop_signal, graceful_timeout then SIGKILL)

              kill_processes(*args, **kwargs)
                     Kill all processes (stop_signal, graceful_timeout then SIGKILL)

              manage_processes(*args, **kwargs)
                     Manage processes.

              notify_event(topic, msg)
                     Publish a message on the event publisher channel

              reap_and_manage_processes(*args, **kwargs)
                     Reap & manage processes.

              reap_processes(*args, **kw)
                     Reap all the processes for this watcher.

              send_signal_child(*args, **kw)
                     Send signal to a child.

              spawn_process(recovery_wid=None)
                     Spawn process.

                     Return True if ok, False if the watcher must be stopped

              spawn_processes(*args, **kwargs)
                     Spawn processes.

       class circus.arbiter.Arbiter(watchers,  endpoint,  pubsub_endpoint,  check_delay=1.0,  prereload_fn=None,
       context=None,      loop=None,      statsd=False,     stats_endpoint=None,     statsd_close_outputs=False,
       multicast_endpoint=None, plugins=None, sockets=None, warmup_delay=0, httpd=False, httpd_host='localhost',
       httpd_port=8080,     httpd_close_outputs=False,     debug=False,     debug_gc=False,     ssh_server=None,
       proc_name='circusd', pidfile=None, loglevel=None,  logoutput=None,  loggerconfig=None,  fqdn_prefix=None,
       umask=None, endpoint_owner=None, papa_endpoint=None)
              Class used to control a list of watchers.

              Options:

              • watchers -- a list of Watcher objects

              • endpoint -- the controller ZMQ endpoint

              • pubsub_endpoint -- the pubsub endpoint

              • statsd -- If True, a circusd-stats process is run (default: False)

              • stats_endpoint -- the stats endpoint.

              • statsd_close_outputs  --  if  True  sends the circusd-stats stdout/stderr to /dev/null (default:
                False)

              • multicast_endpoint -- the  multicast  endpoint  for  circusd  cluster  auto-discovery  (default:
                udp://237.219.251.97:12027)  Multicast  addr  should be between 224.0.0.0 to 239.255.255.255 and
                the same for the all cluster.

              • check_delay -- the delay between two controller points (default: 1 s)

              • prereload_fn -- callable that will be executed on each reload (default: None)

              • context -- if provided, the zmq context to reuse.  (default: None)

              •

                loop: if provided, a zmq.eventloop.ioloop.IOLoop instance
                       to reuse. (default: None)

              • plugins -- a list of plugins. Each item is a mapping with:

                   • use -- Fully qualified name that points to the plugin class

                   • every other value is passed to the plugin in the config option

              • sockets -- a mapping of sockets. Each key is the socket name,  and  each  value  a  CircusSocket
                class. (default: None)

              • warmup_delay -- a delay in seconds between two watchers startup.  (default: 0)

              • httpd -- If True, a circushttpd process is run (default: False)

              • httpd_host -- the circushttpd host (default: localhost)

              • httpd_port -- the circushttpd port (default: 8080)

              • httpd_close_outputs -- if True, sends circushttpd stdout/stderr to /dev/null. (default: False)

              • debug -- if True, adds a lot of debug info in the stdout (default: False)

              • debug_gc  --  if  True,  does gc.set_debug(gc.DEBUG_LEAK) (default: False) to circusd to analyze
                problems (default: False)

              • proc_name -- the arbiter process name

              •

                fqdn_prefix -- a prefix for the unique identifier of the circus
                       instance on the cluster.

              • endpoint_owner -- unix user to chown the endpoint to if using ipc.

              • papa_endpoint -- the papa process kernel endpoint

              add_watcher(*args, **kwargs)
                     Adds a watcher.

                     Options:

                     • name: name of the watcher to add

                     • cmd: command to run.

                     • all other options defined in the Watcher constructor.

              get_watcher(name)
                     Return the watcher name.

              numprocesses()
                     Return the number of processes running across all watchers.

              numwatchers()
                     Return the number of watchers.

              reload(*args, **kwargs)
                     Reloads everything.

                     Run the prereload_fn() callable if any, then gracefuly reload all watchers.

              start(*args, **kwargs)
                     Starts all the watchers.

                     If the ioloop has been provided during __init__() call, starts all watchers as  a  standard
                     coroutine

                     If  the  ioloop  hasn't been provided during __init__() call (default), starts all watchers
                     and the eventloop (and blocks here). In this  mode  the  method  MUST  NOT  yield  anything
                     because it's called as a standard method.

                     Parameters
                            cb -- Callback called after all the watchers have been started, when the loop hasn't
                            been provided.

   Writing plugins
       Circus comes with a plugin system which lets you interact with circusd.

       NOTE:
          We might add circusd-stats support to plugins later on.

       A Plugin is composed of two parts:

       • a ZMQ subscriber to all events published by circusd

       • a ZMQ client to send commands to circusd

       Each plugin is run as a separate process under a custom watcher.

       A few examples of some plugins you could create with this system:

       • a notification system that sends e-mail alerts when a watcher is flapping

       • a logger

       • a tool that adds or removes processes depending on the load

       • etc.

       Circus itself comes with a few built-in plugins.

   The CircusPlugin class
       Circus provides a base class to help you implement plugins: circus.plugins.CircusPlugin

       class circus.plugins.CircusPlugin(endpoint, pubsub_endpoint, check_delay, ssh_server=None, **config)
              Base class to write plugins.

              Options:

              • context -- the ZMQ context to use

              • endpoint -- the circusd ZMQ endpoint

              • pubsub_endpoint -- the circusd ZMQ pub/sub endpoint

              • check_delay -- the configured check delay

              • config -- free config mapping

              call(command, **props)
                     Sends the command to circusd

                     Options:

                     • command -- the command to call

                     • props -- keyword arguments to add to the call

                     Returns the JSON mapping sent back by circusd

              cast(command, **props)
                     Fire-and-forget a command to circusd

                     Options:

                     • command -- the command to call

                     • props -- keyword arguments to add to the call

              handle_init()
                     Called right before a plugin is started - in the thread context.

              handle_recv(data)
                     Receives every event published by circusd

                     Options:

                     • data -- a tuple containing the topic and the message.

              handle_stop()
                     Called right before the plugin is stopped by Circus.

       When initialized by Circus, this class creates its own event loop that receives all  circusd  events  and
       pass them to handle_recv(). The data received is a tuple containing the topic and the data itself.

       handle_recv() must be implemented by the plugin.

       The  call()  and  cast()  methods  can be used to interact with circusd if you are building a Plugin that
       actively interacts with the daemon.

       handle_init() and handle_stop() are just convenience methods you can use to initialize and clean up  your
       code.  handle_init()  is  called within the thread that just started. handle_stop() is called in the main
       thread just before the thread is stopped and joined.

   Writing a plugin
       Let's write a plugin that logs in a file every event happening in circusd. It takes one argument which is
       the filename.

       The plugin may look like this:

          from circus.plugins import CircusPlugin

          class Logger(CircusPlugin):

              name = 'logger'

              def __init__(self, *args, **config):
                  super(Logger, self).__init__(*args, **config)
                  self.filename = config.get('filename')
                  self.file = None

              def handle_init(self):
                  self.file = open(self.filename, 'a+', buffering=1)

              def handle_stop(self):
                  self.file.close()

              def handle_recv(self, data):
                  watcher_name, action, msg = self.split_data(data)
                  msg_dict = self.load_message(msg)
                  self.file.write('%s %s::%r\n' % (action, watcher_name, msg_dict))

       That's it ! This class can be saved in any package/module, as long as it can be seen by Python.

       For example, Logger may be found in a plugins module within a myproject package.

   Async requests
       In  case  you  want  to make any asynchronous operations (like a Tornado call or using periodicCall) make
       sure you are using the right loop. The loop you always want to be using is self.loop as it gets set up by
       the  base  class.  The  default  loop  often  isn't the same and therefore code might not get executed as
       expected.

   Trying a plugin
       You can run a plugin through the command line with the circus-plugin command, by  specifying  the  plugin
       fully qualified name:

          $ circus-plugin --endpoint tcp://127.0.0.1:5555 --pubsub tcp://127.0.0.1:5556 --config filename:circus-events.log myproject.plugins.Logger
          [INFO] Loading the plugin...
          [INFO] Endpoint: 'tcp://127.0.0.1:5555'
          [INFO] Pub/sub: 'tcp://127.0.0.1:5556'
          [INFO] Starting

       Another  way  to  run  a  plugin  is  to  let  Circus handle its initialization. This is done by adding a
       [plugin:NAME] section in the configuration file, where NAME is a unique name for your plugin:

          [plugin:logger]
          use = myproject.plugins.Logger
          filename = /var/myproject/circus.log

       use is mandatory and points to the fully qualified name of the plugin.

       When Circus starts, it creates a watcher with one process that runs the pointed class, and pass any other
       variable contained in the section to the plugin constructor via the config mapping.

       You  can  also  programmatically  add  plugins  when  you  create  a  circus.arbiter.Arbiter class or use
       circus.get_arbiter(), see library.

   Performances
       Since every plugin is loaded in its own process, it should not impact the  overall  performances  of  the
       system as long as the work done by the plugin is not doing too many calls to the circusd process.

   Hooks
       Circus provides hooks that can be used to trigger actions upon watcher events.  Available hooks are:

       • before_start: called before the watcher is started. If the hook returns False the startup is aborted.

       • after_start:  called after the watcher is started. If the hook returns False the watcher is immediately
         stopped and the startup is aborted.

       • before_spawn: called before the watcher spawns a new process.  If the hook returns False the watcher is
         immediately stopped and the startup is aborted.

       • after_spawn:  called  after the watcher spawns a new process.  If the hook returns False the watcher is
         immediately stopped and the startup is aborted.

       • before_stop: called before the watcher is stopped. The hook result is ignored.

       • after_stop: called after the watcher is stopped. The hook result is ignored.

       • before_signal: called before a signal is sent to a watcher's process. If the  hook  returns  False  the
         signal is not sent (except SIGKILL which is always sent)

       • after_signal: called after a signal is sent to a watcher's process.

       • extended_stats:  called  when stats are requested with extended=True.  Used for adding process-specific
         stats to the regular stats output.

   Example
       A typical use case is to control that all the conditions are met for a process to start.  Let's  say  you
       have  a  watcher  that  runs  Redis  and a watcher that runs a Python script that works with Redis.  With
       Circus you can order the startup by using the priority option:

          [watcher:queue-worker]
          cmd = python -u worker.py
          priority = 1

          [watcher:redis]
          cmd = redis-server
          priority = 2

       With this setup, Circus will start Redis first and then it will start the queue worker.  But Circus  does
       not  really control that Redis is up and running. It just starts the process it was asked to start.  What
       we miss here is a way to control that Redis is started and fully functional.  A  function  that  controls
       this could be:

          import redis
          import time

          def check_redis(*args, **kw):
              time.sleep(.5)  # give it a chance to start
              r = redis.StrictRedis(host='localhost', port=6379, db=0)
              r.set('foo', 'bar')
              return r.get('foo') == 'bar'

       This function can be plugged into Circus as an before_start hook:

          [watcher:queue-worker]
          cmd = python -u worker.py
          hooks.before_start = mycoolapp.myplugins.check_redis
          priority = 1

          [watcher:redis]
          cmd = redis-server
          priority = 2

       Once  Circus  has started the redis watcher, it will start the queue-worker watcher, since it follows the
       priority ordering.  Just before starting the second watcher, it will run the check_redis function, and in
       case it returns False will abort the watcher starting process.

   Hook signature
       A hook must follow this signature:

          def hook(watcher, arbiter, hook_name, **kwargs):
              ...
              # If you don't return True, the hook can change
              # the behavior of circus (depending on the hook)
              return True

       Where  watcher is the Watcher class instance, arbiter the Arbiter one, hook_name the hook name and kwargs
       some additional optional parameters (depending on the hook type).

       The after_spawn hook adds the pid parameters:

          def after_spawn(watcher, arbiter, hook_name, pid, **kwargs):
              ...
              # If you don't return True, circus will kill the process
              return True

       Where pid is the PID of the corresponding process.

       Likewise, before_signal and after_signal hooks add pid and signum:

          def before_signal_hook(watcher, arbiter, hook_name, pid, signum, **kwargs):
              ...
              # If you don't return True, circus won't send the signum signal
              # (SIGKILL is always sent)
              return True

       Where pid is the PID of the corresponding process and signum is the corresponding signal.

       You can ignore those but being able to use the watcher and/or arbiter data and methods can be  useful  in
       some hooks.

       Note  that  hooks  are  called  with named arguments. So use the hook signature without changing argument
       names.

       The extended_stats hook has its own additional parameters in kwargs:

          def extended_stats_hook(watcher, arbiter, hook_name, pid, stats, **kwargs):
              ...

       Where pid is the PID of the corresponding process and stats the regular stats to be  returned.  Add  your
       own stats into stats. An example is in examples/uwsgi_lossless_reload.py.

       As a last example, here is a super hook which can deal with all kind of signals:

          def super_hook(watcher, arbiter, hook_name, **kwargs):
              pid = None
              signum = None
              if hook_name in ('before_signal', 'after_signal'):
                  pid = kwargs['pid']
                  signum = kwargs['signum']
              ...
              return True

   Hook events
       Everytime a hook is run, its result is notified as an event in Circus.

       There are two events related to hooks:

       • hook_success:  a hook was successfully called. The event keys are name the name if the event, and time:
         the date of the events.

       • hook_failure: a hook has failed. The event keys are name the name if the event, time: the date  of  the
         events and error: the exception that occurred in the event, if any.

   Adding new commands
       We tried to make adding new commands as simple as possible.

       You need to do three things:

       1. create a your_command.py file under circus/commands/.

       2. Implement a single class in there, with predefined methods

       3. Add the new command in circus/commands/__init__.py.

       Let's  say  we  want  to add a command which returns the number of watchers currently in use, we would do
       something like this (extensively commented to allow you to follow more easily):

          from circus.commands.base import Command
          from circus.exc import ArgumentError, MessageError
          class NumWatchers(Command):
              """It is a good practice to describe what the class does here.

              Have a look at other commands to see how we are used to format
              this text. It will be automatically included in the documentation,
              so don't be affraid of being exhaustive, that's what it is made
              for.
              """
              # all the commands inherit from `circus.commands.base.Command`

              # you need to specify a name so we find back the command somehow
              name = "numwatchers"

              # Set waiting to True or False to define your default behavior
              # - If waiting is True, the command is run synchronously, and the client may get
              #   back results.
              # - If waiting is False, the command is run asynchronously on the server and the client immediately
              #   gets back an 'ok' response
              #
              #   By default, commands are set to waiting = False
              waiting = True

              # options
              options = [('', 'optname', default_value, 'description')]

              properties = ['foo', 'bar']
              # properties list the command arguments that are mandatory. If they are
              # not provided, then an error will be thrown

              def execute(self, arbiter, props):
                  # the execute method is the core of the command: put here all the
                  # logic of the command and return a dict containing the values you
                  # want to return, if any
                  return {"numwatchers": arbiter.numwatchers()}

              def console_msg(self, msg):
                  # msg is what is returned by the execute method.
                  # this method is used to format the response for a console (it is
                  # used for instance by circusctl to print its messages)
                  return "a string that will be displayed"

              def message(self, *args, **opts):
                  # message handles console input.
                  # this method is used to map console arguments to the command
                  # options. (its is used for instance when calling the command via
                  # circusctl)
                  # NotImplementedError will be thrown if the function is missing
                  numArgs = 1
                  if not len(args) == numArgs:
                      raise ArgumentError('Invalid number of arguments.')
                  else:
                      opts['optname'] = args[0]
                  return self.make_message(**opts)

              def validate(self, props):
                  # this method is used to validate that the arguments passed to the
                  # command are correct. An ArgumentError should be thrown in case
                  # there is an error in the passed arguments (for instance if they
                  # do not match together.
                  # In case there is a problem wrt their content, a MessageError
                  # should be thrown. This method can modify the content of the props
                  # dict, it will be passed to execute afterwards.

   Use cases examples
       This chapter presents a few use cases, to give you an idea on how to use Circus in your environment.

   Running a WSGI application
       Running a WSGI application with Circus is quite interesting because you  can  watch  &  manage  your  web
       workers using circus-top, circusctl or the Web interface.

       This is made possible by using Circus sockets. See whycircussockets.

       Let's take an example with a minimal Pyramid application:

          from pyramid.config import Configurator
          from pyramid.response import Response

          def hello_world(request):
              return Response('Hello %(name)s!' % request.matchdict)

          config = Configurator()
          config.add_route('hello', '/hello/{name}')
          config.add_view(hello_world, route_name='hello')
          application = config.make_wsgi_app()

       Save this script into an app.py file, then install those projects:

          $ pip install Pyramid
          $ pip install chaussette

       Next, make sure you can run your Pyramid application using the chaussette console script:

          $ chaussette app.application
          Application is <pyramid.router.Router object at 0x10a4d4bd0>
          Serving on localhost:8080
          Using <class 'chaussette.backend._waitress.Server'> as a backend

       And check that you can reach it by visiting http://localhost:8080/hello/tarek

       Now that your application is up and running, let's create a Circus configuration file:

          [circus]
          check_delay = 5
          endpoint = tcp://127.0.0.1:5555
          pubsub_endpoint = tcp://127.0.0.1:5556
          stats_endpoint = tcp://127.0.0.1:5557

          [watcher:webworker]
          cmd = chaussette --fd $(circus.sockets.webapp) app.application
          use_sockets = True
          numprocesses = 3

          [socket:webapp]
          host = 127.0.0.1
          port = 8080

       This  file  tells  Circus  to  bind a socket on port 8080 and run chaussette workers on that socket -- by
       passing its fd.

       Save it to server.ini and try to run it using circusd

          $ circusd server.ini
          [INFO] Starting master on pid 8971
          [INFO] sockets started
          [INFO] circusd-stats started
          [INFO] webapp started
          [INFO] Arbiter now waiting for commands

       Make sure you still get the app on http://localhost:8080/hello/tarek.

       Congrats ! you have a WSGI application running 3 workers.

       You can run the circushttpd or the cli, and enjoy Circus management.

   Running a Django application
       Running a Django application is done exactly like running a  WSGI  application.  Use  the  PYTHONPATH  to
       import the directory the project is in, the directory that contains the directory that has settings.py in
       it (with Django 1.4+ this directory has manage.py in it) :

          [socket:dwebapp]
          host = 127.0.0.1
          port = 8080

          [watcher:dwebworker]
          cmd = chaussette --fd $(circus.sockets.dwebapp) dproject.wsgi.application
          use_sockets = True
          numprocesses = 2

          [env:dwebworker]
          PYTHONPATH = /path/to/parent-of-dproject

       If you need to pass the DJANGO_SETTINGS_MODULE for a backend worker for example, you can pass  that  also
       though the env configation option:

          [watcher:dbackend]
          cmd = /path/to/script.py
          numprocesses=3

          [env:dbackend]
          PYTHONPATH = /path/to/parent-of-dproject
          DJANGO_SETTINGS_MODULE=dproject.settings

       See http://chaussette.readthedocs.org for more about chaussette.

   Design decisions
   Overall architecture
       [image]

       Circus  is  composed of a main process called circusd which takes care of running all the processes. Each
       process managed by Circus is a child process of circusd.

       Processes are organized in groups called watchers. A watcher is basically a command circusd runs on  your
       system, and for each command you can configure how many processes you want to run.

       The  concept  of  watcher is useful when you want to manage all the processes running the same command --
       like restart them, etc.

       circusd binds two ZeroMQ sockets:

       • REQ/REP -- a socket used to control circusd using json-based commands.

       • PUB/SUB -- a socket where circusd publishes events, like when a process is started or stopped.

       NOTE:
          Despite its name, ZeroMQ  is  not  a  queue  management  system.  Think  of  it  as  an  inter-process
          communication (IPC) library.

       Another  process called circusd-stats is run by circusd when the option is activated. circusd-stats's job
       is to publish CPU/Memory usage statistics in a dedicated PUB/SUB channel.

       This specialized channel is used by circus-top and circus-httpd to display a live stream of the activity.

       circus-top is a console script that mimics top to display all the CPU and Memory usage of  the  processes
       managed by Circus.

       circus-httpd  is  the  web managment interface that will let you interact with Circus. It displays a live
       stream using web sockets and the circusd-stats channel, but also let you interact with  circusd  via  its
       REQ/REP channel.

       Last but not least, circusctl is a command-line tool that let you drive circusd via its REQ/REP channel.

       You  can  also  have plugins that subscribe to circusd's PUB/SUB channel and let you send commands to the
       REQ/REP channel like circusctl would.

   Security
       Circus is built on the top of the ZeroMQ library and comes with no security  at  all  in  its  protocols.
       However,  you  can  run  a  Circus  system on a server and set up an SSH tunnel to access it from another
       machine.

       This section explains what Circus does on your system when you run it, and ends up describing how to  use
       an SSH tunnel.

       You can also read http://www.zeromq.org/area:faq#toc5

   TCP ports
       By default, Circus opens the following TCP ports on the local host:

       • 5555 -- the port used to control circus via circusctl5556 -- the port used for the Publisher/Subscriber channel.

       • 5557 -- the port used for the statistics channel -- if activated.

       • 8080 -- the port used by the Web UI -- if activated.

       These  ports  allow  client  apps  to  interact  with  your  Circus  system,  and  depending  on how your
       infrastructure is organized, you may want to protect these ports via firewalls or configure Circus to run
       using IPC ports.

       Here's an example of running Circus using only IPC entry points:

          [circus]
          check_delay = 5
          endpoint = ipc:///var/circus/endpoint
          pubsub_endpoint = ipc:///var/circus/pubsub
          stats_endpoint = ipc:///var/circus/stats

       When  Configured  using  IPC, the commands must be run from the same box, but no one can access them from
       outside, unlike using TCP. The commands must also be run as a user that  has  write  access  to  the  ipc
       socket  paths.  You  can  modify  the  owner of the endpoint using the endpoint_owner config option. This
       allows you to run circusd as the root user, but allow non-root processes to  send  commands  to  circusd.
       Note  that  when  using  endpoint_owner,  in order to prevent non-root processes from being able to start
       arbitrary processes that run with greater privileges, the add command will enforce that new Watchers must
       run  as  the  endpoint_owner  user.  Watcher definitions in the local config files will not be restricted
       this way.

       Of course, if you activate the Web UI, the 8080 port will still be open.

   circushttpd
       When you run circushttpd manually, or when you use the httpd option in the ini file like this:

          [circus]
          check_delay = 5
          endpoint = ipc:///var/circus/endpoint
          pubsub_endpoint = ipc:///var/circus/pubsub
          stats_endpoint = ipc:///var/circus/stats
          httpd = 1

       The web application will run on port 8080 and will let anyone accessing the web page manage  the  circusd
       daemon.

       That includes creating new watchers that can run any command on your system !

       Do not make it publicly available

       If  you  want  to  protect  the  access  to the web panel, you can serve it behind Nginx or Apache or any
       proxy-capable web server, that can take care of the security.

   User and Group Permissions
       By default, all processes started with Circus will be running with the same user and  group  as  circusd.
       Depending  on  the  privileges  the  user  has on the system, you may not have access to all the features
       Circus provides.

       For instance, some statistics features on a running processes require extended privileges. Typically,  if
       the  CPU  usage numbers you get using the stats command are N/A, it means your user can't access the proc
       files. This will be the case by default under Mac OS X.

       You may run circusd as root to fix this, and set the uid and gid values for each watcher to get  all  the
       features.

       But  beware  that running circusd as root exposes you to potential privilege escalation bugs. While we're
       doing our best to avoid any bugs, running as root and facing a bug that performs unwanted actions on your
       system may be dangerous.

       The  best way to prevent this is to make sure that the system running Circus is completely isolated (like
       a VM) or to run the whole system under a controlled user.

   SSH tunneling
       Clients can connect to a circusd instance by creating an SSH tunnel.  To do so,  pass  the  command  line
       option  --ssh  followed  by  user@address, where user is the user on the remote server and address is the
       server's address as seen by the client.  The SSH protocol will require credentials to complete the login.

       If circusd as seen by the SSH server is not at the default endpoint address localhost:5555  then  specify
       the circusd address using the option --endpoint

   Secured setup example
       Setting up a secured Circus server can be done by:

       • Running an SSH Server

       • Running Apache or Nginx on the 80 port, and doing a reverse-proxy on the 8080 port.

       • Blocking the 8080 port from outside access.

       • Running all ZMQ Circusd ports using IPC files instead of TCP ports, and tunneling all calls via SSH.
       [image]

   Contributing to Circus
       Circus  has been started at Mozilla but its goal is not to stay only there.  We're trying to build a tool
       that's useful for others, and easily extensible.

       We really are open to any contributions,  in  the  form  of  code,  documentation,  discussions,  feature
       proposal etc.

       You can start a topic in our mailing list : http://tech.groups.yahoo.com/group/circus-dev/

       Or add an issue in our bug tracker

   Fixing typos and enhancing the documentation
       It's  totally  possible  that  your  eyes  are  bleeding  while  reading  this  half-english  half-french
       documentation,  don't  hesitate  to  contribute  any  rephrasing  /  enhancement  on  the  form  in   the
       documentation. You probably don't even need to understand how Circus works under the hood to do that.

   Adding new features
       New  features  are  of  course  very  much  appreciated. If you have the need and the time to work on new
       features, adding them to Circus shouldn't be that complicated. We tried very hard to  have  a  clean  and
       understandable API, hope it serves the purpose.

       You  will need to add documentation and tests alongside with the code of the new feature. Otherwise we'll
       not be able to accept the patch.

   How to submit your changes
       We're using git as a DVCS. The best way to propose changes is to create a branch on your  side  (via  git
       checkout  -b  branchname)  and  commit  your changes there. Once you have something ready for prime-time,
       issue a pull request against this branch.

       We are following this model to allow to have low coupling between the features  you  are  proposing.  For
       instance, we can accept one pull request while still being in discussion for another one.

       Before  proposing  your  changes,  double  check that they are not breaking anything! You can use the tox
       command to ensure this, it will run the testsuite under the different supported python versions.

       Please use : http://issue2pr.herokuapp.com/ to reference a commit to an existing circus issue, if any.

   Avoiding merge commits
       Avoiding merge commits allows to have a clean and readable history. To do so, instead of doing "git pull"
       and  letting  git  handling  the  merges for you, using git pull --rebase will put your changes after the
       changes that are commited in the branch, or when working on master.

       That is, for us core developers, it's not possible anymore to use the handy github green button  on  pull
       requests  if  developers  didn't  rebased  their  work themselves or if we wait too much time between the
       request and the actual merge. Instead, the flow looks like this:

          git remote add name repo-url
          git fetch name
          git checkout feature-branch
          git rebase master

          # check that everything is working properly and then merge on master
          git checkout master
          git merge feature-branch

   Discussing
       If you find yourself in need of any help while looking at the code of Circus, you can go and find  us  on
       irc at #circus-tent on irc.freenode.org (or if you don't have any IRC client, use the webchat)

       You can also start a thread in our mailing list - http://tech.groups.yahoo.com/group/circus-dev

   Frequently Asked Questions
       Here is a list of frequently asked questions about Circus:

   How does Circus stack compare to a classical stack?
       In a classical WSGI stack, you have a server like Gunicorn that serves on a port or an unix socket and is
       usually deployed behind a web server like Nginx: [image]

       Clients call Nginx, which reverse proxies all the calls to Gunicorn.

       If you want to make sure the Gunicorn process stays up and running,  you  have  to  use  a  program  like
       Supervisord or upstart.

       Gunicorn in turn watches for its processes ("workers").

       In  other  words  you  are  using  two  levels  of  process  managment.  One  that you manage and control
       (supervisord), and a second one that you have to manage in a different UI, with  a  different  philosophy
       and less control over what's going on (the wsgi server's one)

       This  is  true  for Gunicorn and most multi-processes WSGI servers out there I know about. uWsgi is a bit
       different as it offers plethoras of options.

       But if you want to add a Redis server in your stack, you will end up with managing your  stack  processes
       in two different places.

       Circus' approach on this is to manage processes and sockets.

       A Circus stack can look like this: [image]

       So,  like Gunicorn, Circus is able to bind a socket that will be proxied by Nginx. Circus don't deal with
       the requests but simply binds the socket. It's then up to a web worker process to accept  connections  on
       the socket and do the work.

       It  provides  equivalent features than Supervisord but will also let you manage all processes at the same
       level, wether they are web workers or Redis or whatever. Adding a new web worker  is  done  exactly  like
       adding a new Redis process.

   Benches
       We did a few benches to compare Circus & Chaussette with Gunicorn. To summarize, Circus is not adding any
       overhead and you can pick up many different backends for your web workers.

       See:

       • http://blog.ziade.org/2012/06/28/wgsi-web-servers-benchhttp://blog.ziade.org/2012/07/03/wsgi-web-servers-bench-part-2

   How to troubleshoot Circus?
       By default, circusd keeps its logging to stdout rather sparse. This lack of output can make  things  hard
       to troubleshoot when processes seem to be having trouble starting.

       To  increase  the logging circusd provides, try increasing the log level. To see the available log levels
       just use the --help flag.

          $ circus --log-level debug test.ini

       One word of warning. If a process is flapping and the debug log level is turned on, you will see messages
       for  each  start attempt. It might be helpful to configure the app that is flapping to use a warmup_delay
       to slow down the messages to a manageable pace.

          [watcher:webapp]
          cmd = python -m myapp.wsgi
          warmup_delay = 5

       By default, stdout and stderr are captured by the circusd process. If you are  testing  your  config  and
       want  to  see  the  output  in  line  with  the circusd output, you can configure your watcher to use the
       StdoutStream class.

          [watcher:webapp]
          cmd = python -m myapp.wsgi
          stdout_stream.class = StdoutStream
          stderr_stream.class = StdoutStream

       If your application is producing a traceback or error when it is trying to start up you should be able to
       see it in the output.

   Changelog history
   0.12.1 - 2015-08-05
       • Fix error when restarting a watcher with an output stream - #913

       • Minor doc tweaks

   0.12 - 2015-06-02
       This release brings Python 3.4, Tornado 4 and Windows support, among several exciting features and fixes.

       The Windows support is still experimental, and does not handle streams.

       Major changes:

       • Compatibility with Python 3.4 - #768

       • Experimental Windows support - #788

       • Compatibility with Tornado 4 - #872

       • Revamped Debian packaging - #896 - #903

       • Add support for Papa process kernel - #850

       • Add globing and regex matching for starting, stopping and restarting watchers - #829 - #902

       More changes:

       • Optimization of the shutdown - #784 - #842

       • Add possibility to specify virtualenv version for the watchers - #805

       • Add --nostop option to the rmwatcher command - #777

       • Add a callback to Arbiter.start - #840

       • Fix reloading watchers with uppercase letters - #823

       • Remove leaking socket in stats daemon - #843

       • Fix multicast on SunOS - #876

       • Close output streams when stopping a watcher - #885

       • Fix signal sending to grandchildren with --recursive - #888

   0.11.1 - 2014-05-22
       • Fixed a regression that broke Circus on 2.6 - #782

   0.11 - 2014-05-21
       This release is not introducing a lot of features, and focused on making Circus more robust & stable.

       Major changes/fixes:

       • Make sure we cannot execute two conflictings commands on the arbiter simultanously.

       • we have 2 new streams class: TimedRotatingFileStream, WatchedFileStream

       • we have one new hook: after_spawn hook

       • CircusPlugin is easier to use

       • fix autostart=False watchers during start (regression)

       More changes:

       • circus messages can be routed to syslog now - #748

       • endpoint_owner option added so we can define which user owns ipc socket files created by circus.

       • Started Windows support (just circusctl for now)

       • fixed a lot of leaks in the tests

       • Allow case sensitive environment variables

       • The resource plugin now accepts absolute memory values - #609

       • Add support to the add command for the 'singleton' option - #767

       • Allow sending arbitrary signals to child procs via resource watcher - #756

       • Allow INI/JSON/YAML configuration for logging

       • Make sure we're compatible with psutil 2.x and 3.x

       • Added more metrics to the statsd provider - #698

       • Fixed multicast discovery - #731

       • Make start, restart and reload more uniform - #673

       • Correctly initialize all use groups - #635

       • improved tests stability

       • many, many more things....

   0.10 - 2013-11-04
       Major changes:

       • Now Python 3.2 & 3.3 compatible - #586

       • Moved the core to a fully async model - #569

       • Improved documentation - #622

       More changes:

       • Added stop_signal & stop_children - #594

       • Make sure the watchdog plugin closes the sockets - #588

       • Switched to ZMQ JSON parser

       • IN not supported on all platforms - #573

       • Allow global environment substitutions in any config section - #560

       • Allow dashes in sections names - #546

       • Now variables are expanded everywhere in the config - #554

       • Added the CommandReloader plugin

       • Added before_signal & after_signal hooks

       • Allow flapping plugin to retry indefinitely

       • Don't respawn procs when the watcher is stopping - #529 - #536

       • Added a unique id for each client message - #517

       • worker ids are now "slots" -

       • Fixed the graceful shutdown behavior - #515

       • Make sure we can add watchers even if the arbiter is not started - #503

       • Make sure make sure we pop expired process - #510

       • Make sure the set command can set several hooks

       • Correctly support ipv6 sockets - #507

       • Allow custom options for stdout_stream and stderr_stream - #495

       • Added time_format for FileStream - #493

       • Added new socket config option to bind to a specific interface by name

   0.9.3 - 2013-09-04
       • Make sure we can add watchers even if the arbiter is not started

       • Make sure we pop expired process

       • Make sure the set command can set one or several hooks

       • Correctly support ipv6 sockets and improvments of CircusSockets

       • Give path default value to prevent UnboundLocalError

       • Added a test for multicast_endpoint existence in Controller initialization

       • Not converting every string of digits to ints anymore

       • Add tests

       • No need for special cases when converting stdout_stream options

       • also accept umask as an argument for consistency

       • Allow custom options for stdout_stream and stderr_stream.

       • Add new socket config option to bind to a specific interface by name

       • Add time_format for FileStream + tests

       • Update circus.upstart

   0.9.2 - 2013-07-17
       • When  a PYTHONPATH is defined in a config file, it's loaded in sys.path so hooks can be located there -
         #477, #481

       • Use a single argument for add_callback so it works with PyZMQ < 13.1.x - see #478

   0.9 - 2013-07-16
       • added [env] sections wildcards

       • added global [env] secrtion

       • fixed hidden exception when circus-web is not installed - #424

       • make sure incr/decr commands really us the nb option - #421

       • Fix watcher virtualenv site-packages not in PYTHONPATH

       • make sure we dont try to remove more processes than 0 - #429

       • updated bootstrap.py - #436

       • fixed multiplatform separator in pythonpath virtualenv watcher

       • refactored socket close function

       • Ensure env sections are applied to all watchers - #437

       • added the reloadconfig command

       • added circus.green and removed gevent from the core - #441, #452

       • silenced spurious stdout & warnings in the tests - #438

       • $(circus.env.*) can be used for all options in the config now

       • added a before_spawn hook

       • correct the path of circusd in systemd service file - #450

       • make sure we can change hooks and set streams via CLI - #455

       • improved doc

       • added a spawn_count stat in watcher

       • added min_cpu and min_mem parameters in ResourceWatcher plugin

       • added the FQDN information to the arbiter.

   0.8.1 - 2013-05-28
       • circusd-stats was choking on unix sockets - #415

       • circusd-stats & circushttpd child processes stdout/stderr are now left open by default. Python <= 2.7.5
         would choke in the logging module in case the 2/3 fds were closed - #415

       • Now redirecting to /dev/null in the child process instead of closing.  #417

   0.8 - 2013-05-24
       • Integrated log handlers into zmq io loop.

       • Make redirector restartable and subsequently more robust.

       • Uses zmq.green.eventloop when gevent is detected

       • Added support for CIRCUSCTL_ENDPOINT environment variable to circusctl - #396

       • util: fix bug in to_uid function - #397

       • Remove handler on ioloop error - #398.

       • Improved test coverage

       • Deprecated the 'service' option for the ResourceWatcher plugin - #404

       • removed psutil.error usage

       • Added UDP discovery in circusd - #407

       • Now allowing globs at arbitrary directory levels - #388

       • Added the 'statd' configuration option - #408

       • Add pidfile, logoutput and loglevel option to circus configuration file - #379

       • Added a tutorial in the docs.

       • make sure we're merging all sections when using include - #414

       • added pipe_stdout, pipe_stderr, close_child_stderr & close_child_stdout options to the Process class

       • added close_child_stderr & close_child_stdout options to the watcher

   0.7.1 - 2013-05-02
       • Fixed the respawn option - #382

       • Make sure we use an int for the timeout - #380

       • display the unix sockets as well -  #381

       • Make sure it works with the latest pyzmq

       • introduced a second syntax for the fd notation

   0.7 - 2013-04-08
       • Fix get_arbiter example to use a dict for the watchers argument. #304

       • Add some troubleshooting documentation #323

       • Add python buildout support

       • Removed the gevent and the thread redirectors. now using the ioloop - fixes #346. Relates #340

       • circus.web is now its own project

       • removed the pyzmq patching

       • Allow the watcher to be configured but not started #283

       • Add an option to load a virtualenv site dir

       • added on_demand watchers

       • added doc about nginx+websockets #371

       • now properly parsing the options list of each command #369

       • Fixed circusd-stats events handling #372

       • fixed the overflow issue in circus-top #378

       • many more things...

   0.6 - 2012-12-18
       • Patching protocols name for sockets - #248

       • Don't autoscale graphs. #240

       • circusctl: add per command help, from docstrings #217

       • Added workers hooks

       • Added Debian package - #227

       • Added Redis, HTTP Observer, Full stats & Resource plugins

       • Now processes can have titles

       • Added autocompletion

       • Added process/watcher age in the webui

       • Added SSH tunnel support

       • Now using pyzmq.green

       • Added upstart script & Varnish doc

       • Added environment variables & sections

       • Added unix sockets support

       • Added the respawn option to have single-run watchers

       • Now using tox in the tests

       • Allow socket substitution in args

       • New doc theme

       • New rotation options for streams: max_bytes/backup_count

   0.5.2 - 2012-07-26
       • now patching the thread module from the stdlib to avoid some Python bugs - #203

       • better looking circusctl help screen

       • uses pustil get_nice() when available (nice was deprecated) - #208

       • added max_age support - #221

       • only call listen() on SOCK_STREAM or SOCK_SEQPACKET sockets

       • make sure the controller empties the plugins list in update_watchers() - #220

       • added --log-level and --log-output to circushttpd

       • fix the process killing via the web UI - #219

       • now circus is zc.buildout compatible for scripts.

       • cleanup the websocket when the client disconnect - #225

       • fixed the default value for the endpoint - #199

       • splitted circushttpd in logical modules

   0.5.1 - 2012-07-11
       • Fixed a bunch of typos in the documentation

       • Added the debug option

       • Package web-requirements.txt properly

       • Added a errno error code in the messages - fixes #111

   0.5 - 2012-07-06
       • added socket support

       • added a listsocket command

       • sockets have stats too !

       • fixed a lot of small bugs

       • removed the wid - now using pid everywhere

       • faster tests

       • changed the variables syntax

       • use pyzmq's ioloop in more places

       • now using iowait for all select() calls

       • incr/decr commands now have an nbprocess parameter

       • Add a reproduce_env option to watchers

       • Add a new UNEXISTING status to the processes

       • Added the global httpd option to run circushttpd as a watcher

   0.4 - 2012-06-12
       • Added a plugin system

       • Added a "singleton" option for watchers

       • Fixed circus-top screen flickering

       • Removed threads from circus.stats in favor of zmq periodic callbacks

       • Enhanced the documentation

       • Circus client now have a send_message api

       • The flapping feature is now a plugin

       • Every command line tool have a --version option

       • Added a statsd plugin (sends the events from circus to statsd)

       • The web UI now uses websockets (via socketio) to get the stats

       • The web UI now uses sessions for "flash messages" in the web ui

   0.3.4 - 2012-05-30
       • Fixed a race condition that prevented the controller to cleanly reap finished processes.

       • Now check_flapping can be controlled in the configuration.  And activated/deactivated per watcher.

   0.3.3 - 2012-05-29
       • Fixed the regression on the uid handling

   0.3.2 - 2012-05-24
       • allows optional args property to add_watcher command.

       • added circushttpd, circus-top and circusd-stats

       • allowing Arbiter.add_watcher() to set all Watcher option

       • make sure the redirectors are re-created on restarts

   0.3.1 - 2012-04-18
       • fix: make sure watcher' defaults aren't overrided

       • added a StdoutStream class.

   0.3 - 2012-04-18
       • added the streaming feature

       • now displaying coverage in the Sphinx doc

       • fixed the way the processes are killed (no more SIGQUIT)

       • the configuration has been factored out

       • setproctitle support

   0.2 - 2012-04-04
       • Removed the show name. replaced by watcher.

       • Added support for setting process rlimit.

       • Added support for include dirs in the config file.

       • Fixed a couple of leaking file descriptors.

       • Fixed a core dump in the flapping

       • Doc improvments

       • Make sure circusd errors properly when another circusd is running on the same socket.

       • get_arbiter now accepts several watchers.

       • Fixed the cmd vs args vs executable in the process init.

       • Fixed --start on circusctl add

   0.1 - 2012-03-20
       • initial release

   man pages
   circusd man page
   Synopsis
       circusd [options] [config]

   Description
       circusd  is the main process of the Circus architecture. It takes care of running all the processes. Each
       process managed by Circus is a child process of circusd.

   Arguments
       config configuration file

   Options
       -h, --help
              Show the help message and exit

       --log-level LEVEL
              Specify the log level. LEVEL can be info, debug, critical, warning or error.

       --log-output LOGOUTPUT
              The location where the logs will be written. The default behavior is to write to stdout  (you  can
              force it by passing '-' to this option). Takes a filename otherwise.

       --logger-config LOGGERCONFIG
              The  location  where  a  standard Python logger configuration INI, JSON or YAML file can be found.
              This can be used to override the default logging configuration for the arbiter.

       --daemon
              Start circusd in the background.

       --pidfile PIDFILE
              The location of the PID file.

       --version
              Displays Circus version and exits.

   See also
       circus (1), circusctl (1), circusd-stats (1), circus-plugin (1), circus-top (1).

       Full Documentation is available at http://circus.readthedocs.org

   circusctl man page
   Synopsis
       circusctl [options] command [args]

   Description
       circusctl is front end to control the Circus daemon. It is designed to help the administrator control the
       functionning of the Circud circusd daemon.

   Commands
       add    Add a watcher

       decr   Decrement the number of processes in a watcher

       dstats Get circusd stats

       get    Get the value of specific watcher options

       globaloptions
              Get the arbiter options

       incr   Increment the number of processes in a watcher

       ipython
              Create shell into circusd process

       list   Get list of watchers or processes in a watcher

       listen Subscribe to a watcher event

       listsockets
              Get the list of sockets

       numprocesses
              Get the number of processes

       numwatchers
              Get the number of watchers

       options
              Get the value of all options for a watcher

       quit   Quit the arbiter immediately

       reload Reload the arbiter or a watcher

       reloadconfig
              Reload the configuration file

       restart
              Restart the arbiter or a watcher

       rm     Remove a watcher

       set    Set a watcher option

       signal Send a signal

       start  Start the arbiter or a watcher

       stats  Get process infos

       status Get the status of a watcher or all watchers

       stop   Stop watchers

   Options
       --endpoint ENDPOINT
              connection endpoint

       -h, --help
              Show the help message and exit

       --json output to JSON

       --prettify
              prettify output

       --ssh SSH
              SSH Server in the format user@host:port

       --ssh_keyfile SSH_KEYFILE
              path to the keyfile to authorise the user

       --timeout TIMEOUT
              connection timeout

       --version
              Displays Circus version and exits.

   See Also
       circus (1), circusd (1), circusd-stats (1), circus-plugin (1), circus-top (1).

       Full Documentation is available at http://circus.readthedocs.org

   circus-plugin man page
   Synopsis
       circus-plugin [options] [plugin]

   Description
       circus-plugin allows to launch a plugin from a running Circus daemon.

   Arguments
       plugin Fully qualified name of the plugin class.

   Options
       --endpoint ENDPOINT
              Connection endpoint.

       --pubsub PUBSUB
              The circusd ZeroMQ pub/sub socket to connect to.

       --config CONFIG
              The plugin configuration file.

       --check-delay CHECK_DELAY
              Check delay.

       --log-level LEVEL
              Specify the log level. LEVEL can be info, debug, critical, warning or error.

       --log-output LOGOUTPUT
              The  location  where the logs will be written. The default behavior is to write to stdout (you can
              force it by passing '-' to this option). Takes a filename otherwise.

       --ssh SSH
              SSH Server in the format user@host:port.

       -h, --help
              Show the help message and exit.

       --version
              Displays Circus version and exits.

   See also
       circus (1), circusd (1), circusctl (1), circusd-stats (1), circus-top (1).

       Full Documentation is available at http://circus.readthedocs.org

   circus-top man page
   Synopsis
       circus-top [options]

   Description
       circus-top is a top-like command to display the Circus daemon and processes managed by circus.

   Options
       --endpoint ENDPOINT
              Connection endpoint.

       --ssh SSH
              SSH Server in the format user@host:port.

       --process-timeout PROCESS_TIMEOUT
              After this delay of inactivity, a process will be removed.

       -h, --help
              Show the help message and exit.

       --version
              Displays Circus version and exits.

   See also
       circus (1), circusctl (1), circusd (1), circusd-stats (1), circus-plugin (1).

       Full Documentation is available at http://circus.readthedocs.org

   circusd-stats man page
   Synopsis
       circusd-stats [options]

   Description
       circusd-stats runs the stats aggregator for Circus.

   Options
       --endpoint ENDPOINT
              Connection endpoint.

       --pubsub PUBSUB
              The circusd ZeroMQ pub/sub socket to connect to.

       --statspoint STATSPOINT
              The ZeroMQ pub/sub socket to send data to.

       --log-level LEVEL
              Specify the log level. LEVEL can be info, debug, critical, warning or error.

       --log-output LOGOUTPUT
              The location where the logs will be written. The default behavior is to write to stdout  (you  can
              force it by passing '-' to this option). Takes a filename otherwise.

       --ssh SSH
              SSH Server in the format user@host:port.

       -h, --help
              Show the help message and exit.

       --version
              Displays Circus version and exits.

   See also
       circus (1), circusd (1), circusctl (1), circus-plugin (1), circus-top (1).

       Full Documentation is available at http://circus.readthedocs.org

   Glossary: Circus-specific terms
       arbiter
              The arbiter is responsible for managing all the watchers within circus, ensuring all processes run
              correctly.

       controller
              A controller contains the set of actions that can be performed on the arbiter.

       flapping
              The flapping detection subscribes to  events  and  detects  when  some  processes  are  constantly
              restarting.

       pub/sub
              Circus has a pubsub that receives events from the watchers and dispatches them to all subscribers.

       remote controller
              The remote controller allows you to communicate with the controller via ZMQ to control Circus.

       watcher, watchers
              A  watcher  is  the  program you tell Circus to run.  A single Circus instance can run one or more
              watchers.

       worker, workers, process, processes
              A process is an independent OS process instance of your program.  A single watcher can run one  or
              more processes. We also call them workers.

   Copyright
       Circus was initiated by Tarek Ziade and is licenced under APLv2

       Benoit Chesneau was an early contributor and did many things, like most of the circus.commands work.

   Licence
          Copyright 2012 - Mozilla Foundation
          Copyright 2012 - Benoit Chesneau

          Licensed under the Apache License, Version 2.0 (the "License");
          you may not use this file except in compliance with the License.
          You may obtain a copy of the License at

              http://www.apache.org/licenses/LICENSE-2.0

          Unless required by applicable law or agreed to in writing, software
          distributed under the License is distributed on an "AS IS" BASIS,
          WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
          See the License for the specific language governing permissions and
          limitations under the License.

   Contributors
       See the full list at https://github.com/circus-tent/circus/blob/master/CONTRIBUTORS.txt

AUTHOR

       Mozilla Foundation, Benoit Chesneau