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Priority Order Startup for Supervisor

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 program reaches a particular process state. When configured it will wait till a supervisor subprocess get's to the configured state, then starts the next process. The next process is determined by priority.

Caveats

This does not solve every situation. If what you need is everything starting up one by one, then this will likely solve your issue. If you need to mix and match which starts in parallel and which in serial (dependencies) this is probably not what you want.

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

Configuration

Configuration requires several things. First you need to configure this software as a event listener:

[eventlistener:inorder]
command=/path/to/ordered-startup-listener
autostart=true
events=PROCESS_STATE

This is probably the only thing you want to autostart. It needs xml rpc api, so don't forget to configure that. A full example is shown later.

There are 2 additional configurations that can be put in a [program: section. These are:

startinorder
This must be set to true in order to have the next process in the line to be started after this one.
startnextafter
This is optional and is defaulted to RUNNING. If you want the process to exit before continuing then set this to EXITED (this is useful for initialization scripts that have to finish before something else starts). This is case insensitive.

Example

The following is an example of a supervisor configuration that starts one item after the next in priority order. The order will be ping, sleep, ping2, and ping3. The ping jobs are configured to wait till they have exited before the next job is started (this is commonly used for initialization scripts that need to complete before continuing).

First supervisord.conf:

[supervisord]
nodaemon=true

[inet_http_server]
port=127.0.0.1:9001

[supervisorctl]
serverurl=http://127.0.0.1:9001

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

[eventlistener:inorder]
command=/path/to/ordered-startup-listener
autostart=true
events=PROCESS_STATE

[include]
files=supervisord.d/*.conf

Next we will look at the jobs in the supervisord.d directory like supervisord.d/ping.conf:

[program:ping]
command=/sbin/ping -c1 www.google.com
priority=100
startsecs=0
autorestart=false
autostart=false
startinorder=true
startnextafter=exited

supervisord.d/ping2.conf:

[program:ping2]
command=/sbin/ping -c1 www.google.com
priority=200
startsecs=0
autorestart=false
autostart=false
startinorder=true
startnextafter=exited

supervisord.d/ping3.conf:

[program:ping3]
command=/sbin/ping -c1 www.google.com
priority=400
startsecs=0
autorestart=false
autostart=false
startinorder=true
startnextafter=exited

supervisord.d/sleep.conf:

[program:sleep]
command=/bin/sleep 60
priority=101
startsecs=5
autorestart=true
autostart=false
startinorder=true

Notice how all of the program: sections have autostart=false. Finally let's look at the output of running supervisord:

2016-10-08 12:15:22,014 INFO Increased RLIMIT_NOFILE limit to 1024
2016-10-08 12:15:22,015 INFO Included extra file "/Users/jason.corbett/tmp/supervisor/supervisord.d/ping.conf" during parsing
2016-10-08 12:15:22,015 INFO Included extra file "/Users/jason.corbett/tmp/supervisor/supervisord.d/ping2.conf" during parsing
2016-10-08 12:15:22,015 INFO Included extra file "/Users/jason.corbett/tmp/supervisor/supervisord.d/ping3.conf" during parsing
2016-10-08 12:15:22,015 INFO Included extra file "/Users/jason.corbett/tmp/supervisor/supervisord.d/sleep.conf" during parsing
2016-10-08 12:15:22,044 INFO RPC interface 'supervisor' initialized
2016-10-08 12:15:22,044 CRIT Server 'inet_http_server' running without any HTTP authentication checking
2016-10-08 12:15:22,045 INFO supervisord started with pid 39396
2016-10-08 12:15:23,050 INFO spawned: 'inorder' with pid 39402
2016-10-08 12:15:23,325 INFO spawned: 'ping' with pid 39403
2016-10-08 12:15:23,325 INFO success: ping entered RUNNING state, process has stayed up for > than 0 seconds (startsecs)
2016-10-08 12:15:23,359 INFO exited: ping (exit status 0; expected)
2016-10-08 12:15:24,048 INFO success: inorder entered RUNNING state, process has stayed up for > than 1 seconds (startsecs)
2016-10-08 12:15:24,052 INFO spawned: 'sleep' with pid 39404
2016-10-08 12:15:29,051 INFO success: sleep entered RUNNING state, process has stayed up for > than 5 seconds (startsecs)
2016-10-08 12:15:29,055 INFO spawned: 'ping2' with pid 39410
2016-10-08 12:15:29,056 INFO success: ping2 entered RUNNING state, process has stayed up for > than 0 seconds (startsecs)
2016-10-08 12:15:29,069 INFO exited: ping2 (exit status 0; expected)
2016-10-08 12:15:29,072 INFO spawned: 'ping3' with pid 39411
2016-10-08 12:15:29,072 INFO success: ping3 entered RUNNING state, process has stayed up for > than 0 seconds (startsecs)
2016-10-08 12:15:29,084 INFO exited: ping3 (exit status 0; expected)
2016-10-08 12:16:24,059 INFO exited: sleep (exit status 0; expected)
2016-10-08 12:16:24,061 INFO spawned: 'sleep' with pid 39452
2016-10-08 12:16:29,059 INFO success: sleep entered RUNNING state, process has stayed up for > than 5 seconds (startsecs)

All of the processes started in order. ping2 started after sleep was RUNNING (influenced by startsecs). When sleep respawned it didn't restart the chain, it only goes through it once.