Ubuntu Manpage: gdnsdctl - Control socket client for gdnsd

NAME

       gdnsdctl - Control socket client for gdnsd

SYNOPSIS

         Usage: gdnsdctl [-c /etc/gdnsd] [-s <IP:port>] [-D] [-l] [-t 47] [-o] [-i] <action> [...]
           -c - Configuration directory (def /etc/gdnsd), for finding UNIX control socket path
           -s - TCP control socket address
           -D - Enable verbose debug output
           -l - Send logs to syslog rather than stderr
           -t - Timeout in seconds (def 47, range 5 - 300)
           -o - One-shot mode: do not retry soft failures (comms errors, replace-in-progress)
           -i - Ignore lack of a running daemon for stop, reload-zones, replace,
                and acme-dns-01-flush, reporting success instead of failure in those cases.
         Actions:
           stop - Stops the running daemon
           reload-zones - Reload the running daemon's zone data
           replace - Ask daemon to spawn a takeover replacement of itself (updates code, config, zone data)
           status - Checks the running daemon's status
           stats - Dumps JSON statistics from the running daemon
           states - Dumps JSON monitored states
           acme-dns-01 - Create ACME DNS-01 payloads from additional arguments:
                         <name> <payload> <name> <payload> ... [max %u payloads]
           acme-dns-01-flush - Flush (remove) all ACME DNS-01 payloads added above

DESCRIPTION

       gdnsdctl is the canonical control socket client for gdnsd.  All operations described above
       are synchronous and report success by exiting with exit status zero, or failure by non-
       zero.

       In general gdnsd and gdnsdctl support concurrent execution of disparate actions from
       multiple actors against a single daemon, and everything should eventually faithfully
       report success without any bugs caused by races, if there are no other issues.

       That is to say, for example, things should be reliable if your configuration management is
       routinely executing "gdnsdctl replace" for configuration updates, and another tool is
       independently routinely executing "gdnsdctl reload-zones" as it updates zonefile data,
       while a third set of tooling is doing "gdnsdctl acme-dns-01" commands, even if all 3
       commands collide with near-perfect timing.  Eventually all 3 "gdnsdctl" commands will
       exit, and the resulting state will have all of the configuration, zone data, and challenge
       updates.

       This is also true of multiple independent and overlapping executions of the same action,
       such as multiple "reload-zones" requests proceeding in parallel, or multiple "acme-dns-01"
       requests.

COMMANDLINE OPTION FLAGS

-c Set the configuration directory, defaults to /etc/gdnsd. This is used to find the
main daemon's configuration file and parse it, in case it sets a non-default
"run_dir", which would change the location of the daemon's UNIX control socket path.

-s This tells gdnsdctl to connect to the daemon over a TCP control socket instead of the
usual local UNIX domain socket. See the gdnsd.config(5) docs about "tcp_control" for
more information about configuring the server side of this.

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

-l Sends log output to syslog rather than the default stderr.

-t Sets the timeout in seconds (default 47) for the entire execution. This is enforced
via a process-level SIGALRM timer, but it can run slightly over time in corner cases.

-o One-shot mode. Normally, gdnsdctl will persistently retry to execute the action under
soft failure conditions. The soft failure conditions happen when the daemon is in the
midst of a "replace" operation, or when a communications error occurs after the
connection is initially established (which could be the racy result of catching bad
timing with the old daemon shutting down during a "replace" operation). This disables
the retries and upgrades all soft (retryable) errors to hard (immediately-fatal)
errors.

-i Ignore-dead-daemon mode. Normally, all actions fail if no daemon is currently
running. With this flag set, if the daemon is not currently running, but the action
is one of the limited set where the intent would be accurately reflected by a future
start of the daemon, gdnsdctl will return a successful exit value in spite of the lack
of a running daemon.

The set of commands which currently honor "-i" are: "reload-zones", "stop",
"acme-dns-01-flush", and "replace".

Actions

stop
Synchronously stops the running daemon. Exit status zero means the daemon was
observed to stop as commanded.

With "-i", exit status zero can also mean the daemon was already not running, which
makes "gdnsdctl -i stop" an idempotent stop.

reload-zones
Synchronously reloads the daemon's zonefiles. Exit status zero indicates the
operation completed successfully and the new data is visible to clients.

With "-i", exit status zero can also mean the daemon was not running (if it's started
in the future, the recently-updated zonefiles would be in effect).

replace
Asks the running daemon to spawn a replacement instance of itself. This can be used
for daemon code upgrades and/or configuration changes. The "replace" sequence is
intended to have minimal operational impact from most points of view: it's race-free,
requests are not lost or dropped and there is no pause in processing requests. Stats
data is handed off seamlessly from the old instance to the new one, as is any
ephemeral ACME DNS-01 challenge data. The control socket remains available for new
connections at all times, but the actual processing of new connections is delayed for
a short span of time.

Commands from already-connected control socket clients (like gdnsdctl) can be denied
with a soft failure response during critical time windows of the replace sequence, but
gdnsdctl will wait and retry them afterwards.

The replacement daemon is initially executed as a child of the running daemon and thus
inherits many attributes of its execution environment. The old and new daemons
coordinate a handoff process over an inter-daemon control socket connection. The
handoff process does its best to ensure that if the new daemon fails at any stage of
startup, the old daemon can continue operations as it was before.

DNS listening sockets are handed off in an overlapped fashion: there will be a brief
window of time where client requests can be routed to either daemon randomly, but
there should never be a window where service is unavailable. The control socket
itself is handed off synchronously: the old daemon stops accepting new connections
before the new daemon begins accepting them, and the old daemon re-starts accepting if
the new daemon fails to succeed completely.

Once the old daemon claims the replacement process was successful, gdnsdctl will
monitor the old daemon's exit and then make a fresh connection to the control socket
of the new daemon and check its status. If all of this is successful, the replace
command will finally exit with status zero. It will exit with a non-zero status if
any part of this operation fails for any reason, which should in most conceivable
cases leave the existing daemon fully functional.

All other daemon-state-changing gdnsdctl operations (anything but the readonly actions
"status", "stats", and "states") which might be initiated separately and concurrently
are explicitly blocked by the daemon while the critical part of the replace handoff
sequence is in progress. gdnsdctl will, by default, retry an action repeatedly until
the replace finishes and lets the action through or it reaches the "-t" timeout. The
"-o" flag disables these retries, which will cause the state-changing gdnsdctl actions
to immediately fail during the critical replace window.

Normally, this command will fail if there is no running daemon. However, with "-i",
exit status zero can also mean the daemon was not running (if it's started in the
future, the recently-updated configuration or binary that triggered wanting to execute
the "replace" request would then be in effect).

The retry system works for "replace" vs "replace" as well: if you concurrently execute
several "gdnsdctl replace" commands, one will proceed first and the rest will wait in
retry loops to each take their turn replacing the daemon serially until they've all
done so successfully, unless their gdnsdctl "-t" timeout expires first (each new
daemon will take some time to start, depending on the zonefile count and configuration
complexity).

status
Checks the running daemon's status, reporting its PID and version to stderr.

stats
Dumps JSON statistics from the running daemon to stdout.

states
Dumps JSON monitored states from any configured service health monitors.

acme-dns-01
Injects temporary ACME DNS-01 challenge response payloads as defined by
<https://tools.ietf.org/html/draft-ietf-acme-acme-14> into the running daemon. This
is intended for integration with scripts or services which generate signed
certificates from an ACME-capable certificate authority.

Two or more additional commandline arguments are required, in pairs of "name" and
"payload", where "name" is a valid domainname and "payload" is the challenge response
payload (which, as a SHA-256 output encoded in base64url encoding, should be 43 bytes
long and consist of only alphanumeric characters plus "-" and "_"). A maximum of 100
separate payloads can be specified in a single gdnsdctl invocation.

This example...

gdnsdctl acme-dns-01 example.org 0123456789012345678901234567890123456789012 www.example.org ABCDEFGHIJKLMNOPQRSTUVWXYZ-abcdefghijklmnop

... causes the daemon to temporarily respond to "TXT" requests for the name
"_acme-challenge.example.org." with the first payload above, and similarly with the
second payload for "_acme-challenge.www.example.org.".

Challenge payload responses injected by this command automatically expire after a
short time. The default is 10 minutes, and is configurable via the config option
"acme_challenge_ttl". The actual DNS TTL emitted with the "TXT" responses defaults to
zero (which is highly recommended!) and is controlled by the separate option
"acme_challenge_dns_ttl".

Injecting responses for domainnames that are not within the scope of one of the
statically-configured zones will succeed, but the response to such queries will still
be "REFUSED" (until such a zone later appears, if ever).

If more than one payload is configured for a given name (in the same command, or in
separate commands less than the TTL window apart), multiple TXT records will be
emitted. If there is any statically-configured TXT data from zonefiles at a
conflicting "_acme-challenge" name, the static TXT RRs will also be served alongside
any data from this mechanism.

As an implementail detail (quirk?) of this mechanism, any static zonefile RRs which
have a first label of "_acme-challenge" will automatically have their TTLs forced to
the "acme_challenge_dns_ttl" regardless of the TTL specified in the zonefile. This
was the easiest way to ensure that we never serve mixed TTL values in a single RR-set
of TXT records, which is forbidden by RFC 2181.

The data injected by this mechanism persists through daemon "replace" operations, but
not through a full "stop" of the daemon. It also persists through zone data reloads,
and in the case that data is injected for a non-existent zone which then comes into
existence through a reload, the challenge will begin working after the reload.

acme-dns-01-flush
Immediately flushes all injected payload data from above ahead of its natural expiry.
Mostly useful for testing or for clearing up mistakes, but some integrations with
spiky large volumes of challenges may wish to flush data explicitly at points in time
when there are no outstanding DNS-01 challenges.

This is another command that honors the "-i" flag: if "-i" is specified and the daemon
is not running, this command will report success, as a dead daemon has no challenge
data to flush.

EXIT STATUS

       In general, all operations exit with status zero if and only if the operation is
       successful.  Errors and most other output go to stderr, except in the case of JSON data
       dumps, which go to stdout.

COPYRIGHT AND LICENSE

       Copyright (c) 2012 Brandon L Black <blblack@gmail.com>

       This file is part of gdnsd.

       gdnsd is free software: you can redistribute it and/or modify it under the terms of the
       GNU General Public License as published by the Free Software Foundation, either version 3
       of the License, or (at your option) any later version.

       gdnsd is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without
       even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
       GNU General Public License for more details.

       You should have received a copy of the GNU General Public License along with gdnsd.  If
       not, see <http://www.gnu.org/licenses/>.