Monitoring Apache Session load with Nagios through mod_status

We needed a Apache web server monitoring that is able to watch the current web server session status. It should alert us for reaching the web servers client session limit with the potentially dropped user sessions that follow.

We are already using Nagios 'check_http' plugin to monitor site access. This plugin also provides the size and access time for the retrieved URL as a perfomance indicator. This data can help identify access performance bottlenecks, but is influenced by the network speed and therefore an very unreliable indicator, as our graphs show.

Although we have historical monitoring that can provide session information (i.e. through webalizer), this is only great to monitor the overall trend. It cannot alarm for ad-hoc session peaks since the information gathered is based on historical log data.

The how-to at:

http://nagios.fm4dd.com/howto/apache-session-monitoring-nagios.htm

describes the setup for Apache session load monitoring using the Apache module 'mod_status'. It has been run under Nagios up to version 4, monitoring Apache2 webservers running on various platforms such as Linux, Windows and AIX.