This tutorial will show you how to monitor an Ubuntu 14.04 server with Munin and Monit. Munin produces nice graphs about nearly every aspect of your server, whereas Monit checks the availability of services like Apache, MySQL, Postfix and takes the appropriate action such as a restart if it finds a service is not behaving as expected.
The combination of the two gives you full monitoring: graphics that let you recognize current or upcoming problems, and a watchdog that ensures the availability of the monitored services. This tutorial contains two (optional) chapters about integrating Munin and Monit into ISPConfig.