Dependency support when starting Supervisor services

supervisord-dependent-startup is a plugin for Supervisor that allows starting up services after dependent services have reached specific states. This plugin is based on ordered-startup-supervisord by Jason Corbett.

The Problem

The problem can be seen in supervisor bug #122. The priority order in supervisor does determine startup order, but when autostart=true supervisor doesn't wait for the previous process to be RUNNING in order to continue. What is even harder is having initialization scripts that need to exit before continuing. This software is meant to make this one use case easier.

How it works

This is an event listener for supervisor. This means it is run by supervisor on startup and supervisor will send it messages whenever a service reaches a particular process state. When configured it will wait till a supervisor subprocess gets to the configured state before starting dependent services.

Caveats

The plugin does not start groups. It can start services that are part of a group, but it won't directly start a group.

Installing

# From pypi
pip install supervisord-dependent-startup

# From github:
pip install -e git+https://github.com/bendikro/supervisord-dependent-startup.git#egg=supervisord-dependent-startup

Configuration

Configuration requires several things. First you need to configure supervisord-dependent-startup as an event listener by adding the following to supervisor.conf:

[eventlistener:dependentstartup]
command=python -m supervisord_dependent_startup
autostart=true
autorestart=unexpected
startretries=0
exitcodes=0,3
events=PROCESS_STATE

A working /etc/supervisor.conf can look like this:

[unix_http_server]
file=/tmp/supervisor.sock ; (the path to the socket file)

[supervisord]
logfile=/tmp/supervisord.log
loglevel=info
pidfile=/var/run/supervisord.pid
nodaemon=false
minfds=1024
minprocs=200

[rpcinterface:supervisor]
supervisor.rpcinterface_factory = supervisor.rpcinterface:make_main_rpcinterface

[supervisorctl]
serverurl=unix:///tmp/supervisor.sock

[eventlistener:dependentstartup]
command=python -m supervisord_dependent_startup
autostart=true
autorestart=unexpected
startretries=0
exitcodes=0,3
events=PROCESS_STATE

[include]
files = /etc/supervisord.d/*.ini

Service configuration options

There are three configuration options for a service ([program:*]) to control how it is processed by supervisord-dependent-startup

dependent_startup

Mark this service to be handled by supervisord-dependent-startup. This must be set to true for all services that depend on other services or is being depended on by other services.

Type	bool
Required	yes
Note	When setting this to true, autostart must be set to false

dependent_startup_wait_for

Specify the services this service depends on before in can be started.

Type	str
Required	no
Format	dependent_startup_wait_for=<parent-service>:<state[,state[..]]> [..]
Note	state must one or more comma separated values of: starting, running, backoff, stopping, exited, fatal

Example with one dependency

To have a service named child depend on a service parent: dependent_startup_wait_for=parent:running

Example with two dependencies

Multiple dependencies are separated by a white space. To have a service named child depend on the services parent1 and parent2: dependent_startup_wait_for=parent1:running parent2:running

dependent_startup_inherit_priority

Specify if the service should inherit its priority from the services it depends on.

Type	bool
Required	no
Example	dependent_startup_inherit_priority=true

Building and testing

Run tests

python setup.py test

Create source dist

python setup.py sdist

Run tests and code syntax check

tox