Sun Cluster 3.1 Data Services Developer's Guide

The Monitor_start Method

The RGM calls the Monitor_start method to start a fault monitor for the resource. Fault monitors monitor the health of the application being managed by the resource. Resource type implementations typically implement a fault monitor as a separate daemon which runs in the background. The Monitor_start callback method is used to launch this daemon with the appropriate arguments.

Because the monitor daemon itself is prone to failures (for example, it could die, leaving the application unmonitored) you should use the PMF to start the monitor daemon. The DSDL utility scds_pmf_start() has built in support for starting fault monitors. This utility uses the relative pathname (relative to the RT_basedir for the location of the resource type callback method implementations) of the monitor daemon program. It uses the Monitor_retry_interval and Monitor_retry_count extension properties managed by the DSDL to prevent unlimited restarts of the daemon. It imposes the same command line syntax as defined for all callback methods (that is, -R resource -G resource_group -T resource_type) onto the monitor daemon, although the monitor daemon is never called directly by the RGM. It allows the monitor daemon implementation itself to leverage the scds_initialize() utility to set up its own environment. The main effort is in designing the monitor daemon itself.