'Service Unavailable' error being displayed on web site

Issue

When browsing your web site, your normal page is now displaying a 'Service Unavailable' error message.

Cause

Each web site runs in it's own IIS Application Pool. An application pool isolates web sites from each other even though they are being hosted on a common server. Each application pool is given its own set of server resources. That way, if a web site crashes, it won’t effect sites in other application pools.

If your web site is showing the 'Service Unavailable' error then it means that your Application Pool has crashed. Application Pools can crash for a number of reasons, such things as buggy code, memory leaks, or random unexpected errors encountered by your scripts. If it only happens once every six months, then it may not be anything to worry about. If it is happening several times a week then it is something you will probably want to look into further.

Solution

The immediate solution is to restart your Application Pool in the Plesk Control Panel. Follow the steps listed in this article to Start your Application Pool.