what is the memmon plugin and how does it work with supervisor

Configuration

To use the `memmon` plugin, you need to add an `[eventlistener:x]` section to your supervisor configuration file (`supervisord.conf`). The configuration includes the following options:

- `command`: specifies the command to run `memmon` with, including the memory limit and email address for notifications.
- `events`: specifies the event to subscribe to, typically `TICK_60` for checking every 60 seconds.
- `cumulative`: checks the cumulative RSS of a process and its children if set to `true`.

Here is an example configuration:

bash
[eventlistener:memmon]
command=memmon -a 200MB -m 
 <script language='JavaScript' type='text/javascript'>
 <!--
 var prefix = 'm&#97;&#105;lt&#111;:';
 var suffix = '';
 var attribs = '';
 var path = 'hr' + 'ef' + '=';
 var addy27611 = 'b&#111;b' + '&#64;';
 addy27611 = addy27611 + '&#101;x&#97;mpl&#101;' + '&#46;' + 'c&#111;m';
 document.write( '<a ' + path + '\'' + prefix + addy27611 + suffix + '\'' + attribs + '>' );
 document.write( addy27611 );
 document.write( '<\/a>' );
 //-->
 </script><script language='JavaScript' type='text/javascript'>
 <!--
 document.write( '<span style=\'display: none;\'>' );
 //-->
 </script>This e-mail address is being protected from spambots. You need JavaScript enabled to view it
 <script language='JavaScript' type='text/javascript'>
 <!--
 document.write( '</' );
 document.write( 'span>' );
 //-->
 </script>
events=TICK_60

How it Works

1. Event Subscription: `memmon` subscribes to the specified event (e.g., `TICK_60`).
2. Memory Check: When the event is triggered, `memmon` checks the RSS of the processes under supervisor control.
3. Restart: If a process exceeds the configured memory limit, `memmon` restarts the process.
4. Notification: If configured, `memmon` sends an email notification to the specified address when a process is restarted.

Limitations

- `memmon` can only monitor processes that are direct children of the supervisor process.
- It does not work on other operating systems besides Linux and Mac OS X.

Installation

The `memmon` plugin is part of the `superlance` package, which can be installed using pip:

bash
pip install superlance

Conclusion

The `memmon` plugin is a useful tool for monitoring and controlling memory usage of processes under supervisor control. It provides a simple and effective way to ensure that processes do not consume excessive memory resources, which can help prevent system crashes and improve overall system performance.