Ubuntu Manpage: gdnsd - An authoritative DNS daemon

NAME

       gdnsd - An authoritative DNS daemon

SYNOPSIS

         Usage: gdnsd [-c /etc/gdnsd] [-D] [-l] [-S] [-R | -i] <action>
           -c - Configuration directory (default /etc/gdnsd)
           -D - Enable verbose debug output
           -l - Send logs to syslog rather than stderr
           -S - Force 'zones_strict_data = true' for this invocation
           -R - Attempt downtimeless replacement of another instance
           -i - Idempotent mode for start/daemonize: exit 0 if already running
                (-R and -i cannot be used together)
         Actions:
           checkconf - Checks validity of config and zone files
           start - Start as a regular foreground process
           daemonize - Start as a background daemon (implies -l)

DESCRIPTION

       gdnsd is very fast, light, and pluggable authoritative DNS daemon.

BASIC CONFIGURATION

       The primary configuration file is the file named config in the configuration directory.

       Note that the configuration file does not have to exist for successful startup.  Without a
       configuration file, gdnsd will load all of the zones in the zones directory (default
       "/etc/gdnsd/zones/") and listen on port 53 of 0.0.0.0 and "::" using default settings.

COMMANDLINE OPTION FLAGS

-c Set the configuration directory, defaults to /etc/gdnsd. The zones directory is the
zones/ subdirectory of the configuration directory.

-D Enables additional debug-level log output as appropriate.

-l Sends log output to syslog rather than the default stderr. This is implicitly turned
on by the "daemonize" action, and is recommended when running as a systemd service as
well, to capture priority information.

-S Forces the "zones_strict_data" configuration option to true for this invocation,
regardless of the setting in the config file. This is mostly useful for validation
during the "checkconf" option.

-R Replace mode for "start" and "daemonize":

Normally, if another server instance has the server control socket locked, a "start"
or "daemonize" attempt will fail. With this flag set, the new server will connect to
the old over its control socket and attempt a downtime-less, graceful takeover of
operations. This allows for both code and configuration changes to happen without
losing requests in most cases and is in general fairly seamless. See the gdnsdctl(8)
documentation for "replace" for more information, as that is the preferred interface
to this functionality.

-i Idempotent mode for "start" and "daemonize":

Normally, if another server instance has the server control socket locked, a "start"
or "daemonize" attempt will fail. With this flag set, if another instance is already
running, this instance will report success and exit with status zero immediately.

ACTIONS

       checkconf
           Checks the validity of the configuration file and zonefiles, setting the exit status
           appropriately (0 for success).  The same code executes implicitly during startup;
           checkconf just exits at the last point before real runtime actions need to be taken,
           such as acquiring sockets.

       start
           Starts gdnsd as a runtime DNS server foreground process, emitting log output to
           stderr.

       daemonize
           Starts gdnsd as a detached background daemonize process in a new session, parented to
           PID 1 (init), emitting log output to directly to syslog.  The initial foreground
           process will emit no terminal output on success, but will wait for the background
           daemon to complete startup operations successfully before exiting with status zero (or
           not, in which case it will exit non-zero and emit some kind of failure output to
           either stderr or syslog).

       Any other commandline option will be treated as invalid, which will result in displaying a
       short help text to STDERR and exiting with a non-zero exit status.  This includes things
       like the ubiquitous --help and --version.

PRIVILEGES

       This service pays no attention to, nor does it attempt to check or modify, anything about
       the runtime security environment or privilege set, or whether or not it happens to be
       running as "root", or attempt any actions that would commonly require "root" privileges,
       such as altering its own memlock rlimits or raising its own process priority.  The lone
       exception is that the code blindly assumes that binding its DNS listening ports, which
       default to being in the privileged range, will Just Work.

       It expects all such things to be managed managed by external mechanisms: either a systemd-
       like init system which can do it all declaratively, or a combination of tooling in an
       initscript for a traditional init system to take care of the necessary privileged settings
       and/or security-jailing / ACLs, etc,

SYSTEMD COMPATIBILITY

       When run as a systemd service, "start" should be used rather than "daemonize", the "-l"
       flag should be used, and the type should be set to "Type=notify" with "NotifyAccess=all".
       The latter bits will cause systemd to set $NOTIFY_SOCKET for the daemon, and the daemon in
       turn will use this to send a readiness notification when it's done with initial startup
       tasks and ready to service requests.  "gdnsdctl -l stop" should be used for the
       "ExecStop=" command.

       The source tree contains an example systemd unit file with reasonable defaults for a
       production deployment.

ZONE FILES - RFC1035

The directory for standard RFC1035 zone files (the default zone data backend) is the
subdirectory named zones/ in the configuration directory, so the default would be
/etc/gdnsd/zones/.

RFC1035 zone files are the traditional zone file format that one typically uses with e.g.
BIND. For more information on the internal format and processing of these files, see
gdnsd.zonefile(5). This section is about how the directory itself is managed.

All files in the zones directory are considered zone files. In general there should be
exactly one file per zone, and the filename should match the zone name. Filenames
beginning with "." are ignored. All zone file must be regular files (as opposed to
directories, symlinks, sockets, etc).

In order to better support the special case of RFC 2137 -style classless in-addr.arpa
delegation zones (which contain forward slashes), any "@" symbol in the filename will be
translated to a forward slash ("/") when transforming a filename into its corresponding
zone name.

For similar reasons, if your server is intended to serve the root of the DNS, the filename
for the root zone should be the special filename ROOT_ZONE, rather than the impossible
literal filename .. Because authoritative servers cannot serve two domains which have a
parent<->child relationship correctly, a root server cannot serve any other zone, so this
would be the sole zonefile.

The standard DNS zone file escape sequences are recognized within the filenames (e.g. "\."
for a dot within a label, or "\NNN" where NNN is a decimal integer in the range 0 - 255),
if for some reason you need a strange character in your zone name.

Trailing dots on zonefile names are ignored; e.g. example.com and example.com. are
functionally equivalent.

Duplicate zones (e.g. having both of the above representations of "example.com" present in
the zones directory, and/or adding a different case-mapping such as EXample.Com) are
illegal.

Subzones (e.g. having zonefiles for both "example.com" and "subz.example.com") are also
illegal.

ZONE FILES - RELOADING

       "gdnsdctl reload-zones" triggers re-loading all zone data.  The reload operation is done
       in a separate thread from the main server and doesn't interrupt DNS request flow.

       "gdnsdctl" will wait for the server to complete the load operation and report back the
       success or failure of the reload transaction via stdout and its process exit status.

       If any failure occurs during the reload operation, the entire reload transaction is
       discarded with no effect on the previous runtime data still in use to answer ongoing
       queries.

DIRECTORIES

Important directory paths for the core daemon code:

/etc/gdnsd
Default configuration directory, unless overridden via "-c". The primary
configuration file is always the file config in the configuration directory.

/run/gdnsd
Default run_dir. This is where the daemon's control socket and lock files are
created. See the entry for "run_dir" in the gdnsd.config(5) manpage for more
information about this directory.

/var/lib/gdnsd
Default state_dir. The admin_state file is read from this directory for
administrative state-overrides on monitored resources, see below in the FILES section.
See the entry for "state_dir" in the gdnsd.config(5) manpage for more information
about this directory.

/usr/libexec/gdnsd
This is the default path for daemon-private executables that users should not run.
The only current case is gdnsd_extmon_helper for the extmon plugin and the path for
this can be overridden in that plugin's configuration, documented in
gdnsd-plugin-extmon(8).

ADMIN STATE FILE - /var/lib/gdnsd/admin_state
This file is the input for administrative state overrides affecting plugin resolution
decisions. The intent of this file is to allow explicit, human administrative decisions
to temporarily override the states affecting plugin decision-making on issues of failover
and/or geographic distribution. A non-existent file is treated the same as an empty file.
The file is watched at runtime for changes, and any overridden state found is applied
quickly. The file is expected to persist reboots and daemon restarts in order to preserve
the administrator's intent through these events.

A basic understanding of how both monitoring and resolution plugins in gdnsd work is
assumed (see gdnsd.config(5)). This file is parsed as a vscf hash data structure (again,
see gdnsd.config(5) for deeper details of that format). The keys are the names of
monitored or virtual resources, and the values are forced state values (optionally with
monitored-TTL values as well). Keys can also be wildcards using the shell glob syntax
which affect multiple resources.

For normal monitored resources, the typical form of a key would be "THING/service_type",
where "THING" is the monitored address or CNAME value and "service_type" is the
service_type configured to monitor that address or CNAME value by one or more resolver
plugins. The value portion takes the form of "STATE[/TTL]", where "STATE" is "UP" or
"DOWN" and the TTL portion is an optional override of the monitored TTL.

The order of the lines in the file is important; they are processed and applied in-order
such that later lines can override the actions of earlier lines. This is especially handy
for making exceptions to glob-matches.

Example:

/var/lib/gdnsd/admin_state:
2001:db8::2:123/my_http_check => DOWN # down a specific res+stype
foo.example.com./extmon_ping => UP # up a specific res+stype
192.0.2.1/* => DOWN # down all service_types for this address
*/xmpp => UP/30 # up all resources monitored by xmpp w/ TTL 30 ...
192.0.2.2/xmpp => DOWN # ... except this one

Some resolution plugins can also register virtual resources (which are not monitored by
any "service_type") solely for the purpose of administrative override of decision-making.
Currently the geoip and metafo plugins do this for their "datacenters", and the keys they
create take the form of "plugin_name/resname/dcname" to force a datacenter's state at the
per-resource level. The geoip plugin also supports keys of the form
"plugin_name/mapname/dcname" to force a datacenter's state at the per-map level. These
forcings override the aggregate state passed up to geoip/metafo from per-datacenter
plugins (e.g. multifo or weighted monitoring several addresses in a datacenter), and in
the geoip case the more-specific per-resource forced state will override any per-map
forced state.