The latest Munin API update includes online help in Drupal advanced_help format, with explanations about Munin API, Munin, RRDtool and MRTG ; hook information for developers of business metrics, and more.
What to do if your Drupal Munin graphs do not appear ?
munin-node starts before Apache (NGinx, etc) is ready, the
munin-drupal plugin won't be able to connect and provide the needed
The Munin APC plugin used to display SMA and Cache info on the same graph, meaning RAM metrics coexisted with hit metrics, like hits, misses, insertions and deletions. Not such a great idea...
Drupal enterprise-class applications and web sites have business-specific metrics to observe: Munin API offers a very simple way to write custom plugins, to monitor exactly the metrics needed by marketing or quality.
Another Munin plugin exists on drupal.org. Munin API is an independent implementation, not derived from the existing project, and strongly differing in architectural choices:
Drupal can provide a Munin heartbeat check too: Munin API can log events if the Munin probe interval deviates from the expected, with 2 levels of severity depending on the deviation: one missed probe could trigger a warning and two a critical.