Provided by: libperlbal-perl_1.80-3_all bug

NAME

       Perlbal::Plugin::Throttle - Perlbal plugin that throttles connections from hosts that
       connect too frequently.

SYNOPSIS

           # in perlbal.conf

           LOAD Throttle

           CREATE POOL web
               POOL web ADD 10.0.0.1:80

           CREATE SERVICE throttler
               SET role                        = reverse_proxy
               SET listen                      = 0.0.0.0:80
               SET pool                        = web

               # adjust throttler aggressiveness
               SET initial_delay               = 10
               SET max_delay                   = 60
               SET throttle_threshold_seconds  = 3
               SET max_concurrent              = 2
               SET ban_threshold               = 4
               SET ban_expiration              = 180

               # limit which requests are throttled
               SET path_regex                  = ^/webapp/
               SET method_regex                = ^GET$

               # allow or ban specific addresses or range (requires Net::CIDR::Lite)
               SET whitelist_file              = conf/whitelist.txt
               SET blacklist_file              = conf/blacklist.txt

               # granular logging (requires Perlbal::Plugin::Syslogger)
               SET log_events                  = ban,unban,throttled,banned
               SET log_only                    = false

               # share state between perlbals (requires Cache::Memcached::Async)
               SET memcached_servers           = 10.0.2.1:11211,10.0.2.2:11211
               SET memcached_async_clients     = 4
               SET instance_name               = mywebapp

               SET plugins                     = Throttle
           ENABLE throttler

DESCRIPTION

       This plugin intercepts HTTP requests to a Perlbal service and slows or drops connections
       from IP addresses which are determined to be connecting too fast.

BEHAVIOR

       An IP address address may be in one of four states depending on its recent activity; that
       state determines how new requests from the IP are handled:

       ·   allowed

           An IP begins in the allowed state. When a request is received from an IP in this
           state, the request is handled immediately and the IP enters the probation state.

       ·   probation

           If no requests are received from an IP in the probation state for
           throttle_threshold_seconds, it returns to the allowed state.

           When a new request is received from an IP in the probation state, the IP enters the
           throttled state and is assigned a delay property initially equal to initial_delay.
           Connection to a backend is postponed for delay seconds while perlbal continues to
           work. If the connection is still open after the delay, the request is then handled
           normally. A dropped connection does not change the IP's delay value.

       ·   throttled

           If no requests are received from an IP in the throttled state for delay seconds, it
           returns to the probation state.

           When a new request is received from an IP in the throttled state, its violations
           property is incremented, and its delay property is doubled (up to a maximum of
           max_delay). The request is postponed for the new value of delay.

           Only after the most recently created connection from a given IP exits the throttled
           state do violations and delay reset to 0.

           Furthermore, if the violations exceeds ban_threshold, the connection is closed and the
           IP moves to the banned state.

           IPs in the throttled state may have no more than max_concurrent connections being
           delayed at once. Any additional requests received in that circumstance are sent a "503
           Too many connections" response. Long-running requests which have already been
           connected to a backend do not count towards this limit.

       ·   banned

           New connections from IPs in the banned state are immediately closed with a 403 error
           response.

           An IP leaves the banned state after ban_expiration seconds have elapsed.

FEATURES

       ·   IP whitelist

           Connections from IPs/CIDRs listed in the file specified by whitelist_file are always
           allowed.

       ·   IP blacklist

           Connections from IPs/CIDRs listed in the file specified by blacklist_file immediately
           sent a "403 Forbidden" response.

       ·   Flexible attack response

           For services where throttling should not normally be enabled, use the default_action
           tunable. When default_action is set to "allow", new connections from
           non-white/blacklisted IPs will not be throttled.

           Furthermore, if throttling should only apply to specific clients, set blacklist_action
           to "throttle". Blacklisted connections will then be throttled instead of denied.

       ·   Dynamic configuration

           Most service tunables may be updated from the management port, after which the new
           values will be respected (although see "CAVEATS"). To reload the whitelist and
           blacklist files, issue the throttle reload whitelist or throttle reload blacklist
           command to the service.

       ·   Path specificity

           Throttling may be restricted to URI paths matching the path_regex regex.

       ·   External shared state

           The plugin stores state which IPs have been seen in a memcached(1) instance.  This
           allows many throttlers to share their state and also minimizes memory use within the
           perlbal. If state exceeds the capacity of the memcacheds, the least-recently seen IPs
           will be forgotten, effectively resetting them to the allowed state.

           Orthogonally, multiple throttlers which need to share memcacheds but not state may
           specify distinct instance_name values.

       ·   Logging

           If Perlbal::Plugin::Syslogger is installed and registered with the service, Throttle
           can use it to send syslog messages regarding actions that are taken.  Granular control
           for which events are logged is available via the log_events parameter. log_events is
           composed of one or more of the following events, separated by commas:

           ·   ban

               Log when a temporary local ban is added for an IP address.

           ·   unban

               Log when a temporary local ban is removed for an IP address.

           ·   whitelisted

               Log when a request is allowed because the source IP is on the whitelist.

           ·   blacklisted

               Log when a request is denied or throttled because the source IP is on the
               blacklist.

           ·   banned

               Log when a request is denied because the source IP is on the temporary ban list
               for connecting excessively.

           ·   concurrent

               Log when a request is denied because the source IP has too many open connections
               waiting to be unthrottled.

           ·   throttled

               Log when a request is throttled because the source IP was not on the whitelist or
               blacklist.

           ·   all

               Enables all the above logging options.

           ·   none

               Disables all the above logging options.

CAVEATS

       ·   Dynamic configuration changes

           Changes to certain service tunables will not be noticed until the throttle reload
           config management command is issued. These include log_events, path_regex, and
           method_regex).

           Changes to certain other tunables will not be respected after the plugin has been
           registered. These include memcached_servers and memcached_async_clients.

       ·   List loading is blocking

           The throttle reload whitelist and throttle reload blacklist management commands load
           the whitelist and blacklist files synchronously, which will cause the perlbal to hang
           until it completes.

       ·   Redirects

           If a handled request returns a 30x response code and the redirect URI is also
           throttled, then the client's attempt to follow the redirect will necessarily be
           delayed by initial_delay. Fixing this would require that the plugin inspect the HTTP
           response headers, which would incur a lot of overhead. To workaround, try to have your
           backend not return 30x's if both the original and redirect URI are proxied by the same
           throttler instance (yes, this is difficult for the case where a backend 302s to add a
           trailing / to a directory).

OPTIONAL DEPENDENCIES

       ·   Cache::Memcached::Async

           Required for memcached support. This is the supported way to share state between
           different perlbal instances.

       ·   Net::CIDR::Lite

           Required for blacklist/whitelist support.

       ·   Perlbal::Plugin::Syslogger

           Required for event logging support.

SEE ALSO

       ·   List of tunables in Throttle.pm.

TODO

       ·   Fix white/blacklist loading

           Load CIDR lists asynchronously (perhaps in the manner of
           Perlbal::Pool::_load_nodefile_async).

AUTHOR

       Adam Thomason, <athomason@cpan.org>

COPYRIGHT AND LICENSE

       Copyright (C) 2007-2011 by Say Media Inc, <cpan@sixapart.com>

       This library is free software; you can redistribute it and/or modify it under the same
       terms as Perl itself, either Perl version 5.8.6 or, at your option, any later version of
       Perl 5 you may have available.