Monit: The Quick Fix

Ideally, in a production system, everything works perfectly. Services never mysteriously crash, free memory is constantly available, and CPU load rarely spikes above 50%. Unfortunately, this is not always the case.

Recently, a client was having issues with their site going down, consistently. They knew it was due to the redis service stopping, but didn't know how to fix it. As a result, one person was perpetually on call, waiting for the site to go down, to run a simple sudo service redis restart.

While it won't fix all of your problems, monit will buy you time, and your sysadmins sleep.

Installing Monit

On CentOS

On Ubuntu

This process creates a configuration file, and adds the command monit to the path.

Configuring Monit

Monit config files are located in different places depending on the system. Ubuntu's config file is located at /etc/monit/monitrc, whereas CentOS uses /etc/monitrc.

Monit config files follow a simple structure, of the form

As an example, below is how we have configured monit to watch redis on a CentOS box that was having memory issues, causing redis to force quit.

In general, monit is a good tool to have in place. Though hopefully it is rarely needed, it prevents issues where someone is called at 3am in order to run a simple command, due to a service crash.