Supervisord listener and symfony command.

Supervisor is a client/server system that allows to monitor and control a number of processes on UNIX-like operating systems.

The intention of this project is to create a Supervisord Listener written in PHP that schedule a task execution. In this case the task is the execution of a Symfony Command Application.

Scenario

Execute 10 times a task within a week. Once execution every 10 minutes.

Solution with cron jobs

The common and ideal solution for many developers is to create a cron job that schedule that task. This solution is out of the scope of this project.

We are focus in solve the problem by using supervisord.

Alternative solution with Supervisord listeners.

An alternative solution is to use the advanced feature Supervisord Listeners

• http://supervisord.org/events.html#configuring-an-event-listener

Supervisord Event Listener implementation using PHP.

The scheduling can be done by using Supervisord TICK_60 event which is defined as (...) an event type that may be subscribed to for event listeners to receive “wake-up” notifications every 60 seconds (...)

Currently, Supervisord only supports TICK_5 (each 5 seconds), TICK_60 (each 60 seconds or 1 minute), TICK_3600 (each 3600 seconds or 1 hour). The selected one to subscribe is TICK_60 event because it's the closer one to the frequency of 10 minutes (600 seconds).

To control throttling information it is used Shared Memory Blocks as storage. Because the task MUST run into an environment, it's sent the environment as an argument.

The scheduled task to execute, when all conditions are met, is a Symfony Console App. As it's a Symfony app there is an environment variable that is required, APP_ENV. Through Supervisord it is possible sending the environment variable value as argument; $argv holds its value. It is set on the Supervisord configuration.

Installation:

• Platform requirement: PHP v7 or higher.
• Supervisord v3.0 or higher.
• The current example runs within Linux OS.

1. Copy the php listener file on a directory In this example we suggest the following linux path: /tmp/supervisord_listener.php. (The selected path can be different. Up to the developer the path)

2. Config the listener on the Supervisord configuration. It can be created within the config file /etc/supervisord.conf or within any of those files included through [include] config option. In out case it's create the file /etc/supervisord.d/listeners.ini and it's included on /etc/supervisord.conf:

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

Listener defined in listeners.ini file :

[eventlistener:listener]
command=php /tmp/supervisord_listener.php %(ENV_APP_ENV)s
events=TICK_60,PROCESS_STATE_RUNNING
user=apache

numprocs=1

Also, you can include: process_name=%(program_name)s-%(process_num)s to set the process name.

Also, it listens PROCESS_STATE_RUNNING event in order to clear shared memory blocks used to save counters values. http://supervisord.org/events.html#process-state-running-event-type

As an argument it's sent %(ENV_APP_ENV)s. The scheduled task to execute, when all conditions are met, is a Symfony Console App. As it's a Symfony app there is an environment variable that is required, APP_ENV. Through supervisord is possible sending the environment variable value as argument. The $argv holds its value.

http://supervisord.org/configuration.html#environment-variables

3. Starting the listener using supervisorctl through the console

• Reloading the listener by executing supervisorctl reload
• Auxiliary we can check the status of the supervisord. Must be RUNNING state. Can be done by executing supervisorctl status
• Auxiliary we can check the output of the supervisord listener protocol. It can be done by executing supervisorctl tail listener. This shows the switching between states.

Contact me

Yenier Jimenez
http://yenierjimenez.net
[email protected]