python supervisord program dependency

supervisord does not directly support dependencies. Your options instead are:

• Use priorities. Set priority for A to a low value and it'll be started before B, and shut down after B. The default value for priority is 999.

  If you put the two programs into one group as well, that'd let you start and stop them in tandem, with the priorities regulating their start and stop order.

• Write an event listener that listens for PROCESS_STATE STARTING-to-RUNNING transition and STOPPING events for A, then instruct supervisord to start and stop B according to those events. Have A autostart, but disable autostarting for B, so that the event handler controls it.

If you want to take a shortcut, and skip reading the documentation about event listeners and skip modifying your programs so they understand events, then:

Instead of starting program B (which depends on A) directly, you could start a Bash script that sleeps until A has been started, and then starts B. For example, if you have a PostgreSQL database and a server that shouldn't start before PostgreSQL:

[program:server]autorestart=truecommand=/.../start-server.sh[program:postgres]user=postgresautorestart=truecommand=/usr/lib/postgresql/9.3/bin/postgres ...

And then inside start-server.sh:

#!/bin/bash# Wait until PostgreSQL started and listens on port 5432.while [ -z "`netstat -tln | grep 5432`" ]; do  echo 'Waiting for PostgreSQL to start ...'  sleep 1doneecho 'PostgreSQL started.'# Start server.echo 'Starting server...'/.../really-start-the-server

One solution is to use supervisorctl: set autostart to false for program B, and in the program launched by A, write supervisorctl start B.

Example:

supervisor.cfg:

[supervisord]nodaemon=falsepidfile=/tmp/supervisor.pidlogfile=/logs/supervisor.log[unix_http_server]file=/var/run/supervisor.sock[rpcinterface:supervisor]supervisor.rpcinterface_factory=supervisor.rpcinterface:make_main_rpcinterface[supervisorctl]serverurl=unix:///var/run/supervisor.sock[program:A]command=do_a[program:B]command=do_bautostart=false

The do_a program contains:

#!/bin/bash#do thingssupervisorctl start B 

TBH it is the solution suggested by @drrzmr but I did not understand it at the time.