Drupal can also be used as a heartbeat check to Munin itself : the Munin API module can emit watchdog events if the Munin probe interval deviates from the normal 300 seconds, with 2 levels of severity depending on the interval: thus one missed probe could trigger a warning and two a critical.
This allows triggering alerts in other systems when Munin itself is down and thus cannot generate the munin-limits alerts.
Settings
This mechanism can be triggered either on cron, or by any hit on a selected path regex. Adjusting the regex allows site administrators to fit the resource consumption vs accuracy compromise to the site activity level.