Monit is a brilliant bit of software that monitors if your services are still up, and can reload them if they die. This definitely helps with first level of support when your servers get a little bit overworked. It can also check that the filesize, checksum and the permissions of the program remained the same.
Installation
The easiest way to install is using apt-get:
sudo apt-get install monit
Configuration
If you want to go with the default config it will run every 2 minutes, and you can view the logs of what was reloaded and when in /var/log/monit.log.
To edit those setting please view the following configuration file:
sudo nano /etc/monit/monitrc
It runs as a service and can be started using the following command
sudo service monit start
Monitoring programs
Below you can find the examples of configuration for nginx and php that will live in /etc/monit/conf.d/
nginx
check process nginx with pidfile /var/run/nginx.pid group webserver start program = "/etc/init.d/nginx start" stop program = "/etc/init.d/nginx stop" if failed host 127.0.0.1 port 80 protocol http and request "/robots.txt" then restart if 3 restarts within 5 cycles then alert
php
check process php5-fpm with pidfile /var/run/php5-fpm.pid group webserver start program = "/etc/init.d/php5-fpm start" stop program = "/etc/init.d/php5-fpm stop" if failed port 80 protocol http request '/index.php' then restart if 3 restarts within 5 cycles then alert depends on nginx
Finish Up
You can add more configuration and you can even add alerting via email or pager duty to let you know when a service fails too many times.
I have used this successfully for a while now, and it saved me a lot of time, as well as helping to fix hard to debug problems with applications and server behaviour
