cs.app.svcd 20190602

SvcD class and "svcd" command to run persistent service programmes.

This provides the features one wants from a daemon for arbitrary commands providing a service:

• process id (pid) files for both svcd and the service command
• filesystem visible status (command running, service enabled) via cs.app.flag <https://pypi.org/project/cs.app.flag/>_
• command restart if the command exits
• command control (stop, restart, disable) via cs.app.flag <https://pypi.org/project/cs.app.flag/>_
• test function to monitor for service viability; if the test function fails, do not run the service. This typically monitors something like network routing (suspend service while laptop offline) or a ping (suspend ssh tunnel while target does not answer pings).
• signature function to monitor for service restart; if the signature changes, restart the service. This typically monitors something like file contents (restart service on configuration change) or network routing (restart ssh tunnel on network change)
• callbacks for service command start and end, for example to display desktop notifications

I use this to run persistent ssh port forwards and a small collection of other personal services. I have convenient shell commands to look up service status and to start/stop/restart services.

See cs.app.portfwd <https://pypi.org/project/cs.app.portfwd/>_ which I use to manage my ssh tunnels; it is a single Python programme running multiple ssh commands, each via its own SvcD instance.

Function main(argv=None)

Command line main programme.

Class SvcD

MRO: cs.app.flag.FlaggedMixin
A process based service.

SvcD.__init__(self, argv, name=None, environ=None, flags=None, group_name=None, pidfile=None, sig_func=None, test_flags=None, test_func=None, test_rate=None, restart_delay=None, once=False, quiet=False, trace=False, on_spawn=None, on_reap=None)

Initialise the SvcD.

    Parameters:
    * `argv`: command to run as a subprocess.
    * `flags`: a cs.app.flag.Flags -like object, default None;
      if None the default flags will be used.
    * `group_name`: alert group name, default "SVCD " + `name`.
    * `pidfile`: path to pid file, default $VARRUN/{name}.pid.
    * `sig_func`: signature function to compute a string which
      causes a restart if it changes
    * `test_flags`: map of {flagname: truthiness} which should
      be monitored at test time; truthy flags must be true and
      untruthy flags must be false
    * `test_func`: test function with must return true if the comannd can run
    * `test_rate`: frequency of tests, default TEST_RATE
    * `restart_delay`: delay before start of an exiting command,
      default RESTART_DELAY
    * `once`: if true, run the command only once
    * `quiet`: if true, do not issue alerts
    * `trace`: trace actions, default False
    * `on_spawn`: to be called after a new subprocess is spawned
    * `on_reap`: to be called after a subprocess is reaped