Ganglia is a completely free, open source, enterprise-grade high performance cluster (of one to many machines) monitoring system cooked up by the good folks at U.C. Berkeley. It’s lightweight, it’s slick, and most important of all, it’s extensible through add-on scripts. What more could you want?
Matt Massie, et al,, Monitoring with Ganglia (O’Reilly, 2012) is a book about the system, It definitely looks like a worthwhile purchase.
The scripting API is very flexible, allowing programs written in shell, perl and python.
Here are a few links to follow up on:
Ganglia Gmetric Repository. Monitor Apache, MySQL, BIND, NFS and Postfix with this collection.
There’s a gmetric script for OpenLDAP. Nothing yet for OpenDJ, 389 Directory or OpenAM, but then I haven’t learned how to program to gmetric yet!