Munin is great, really helps you see how your servers have been doing. The ease in which you can set up plugins on server is great.
Does your apache_processes graph look like this Taken from : http://stats.bit.nl/munin/localdomain/localhost.localdomain/apache_processes.html
Not very useful, the 256 total “available” servers probably isn’t actually how much spare capacity you have, as you will hit MaxClients (something most people tune) before you hit 256 servers. The latest version of Munin sorts this out (optionally) http://munin-monitoring.org/ticket/1210
That gets around the problem, but the real issue is in config (isn’t it always).
The ServerLimit in apache is set to 256 by default, so even if you set MaxClients to say 50, Munin will report the 256 value, meaning you end up with very green graphs as above.
So the simplest fix (if your not on the latest Munin version), is just to have MaxClients == ServerLimit in your apache conf, this will then give you a graph that you can read and gives you some real data to work with.
- I expect there are situations where MaxClients != ServerLimit but for our use case it works.