The High Availability Manager (HAM) provides a mechanism for monitoring processes and services on your system.
The goal is to provide a resilient manager (or “smart watchdog”) that can perform multistage recovery whenever system services or processes fail, no longer respond, or are detected to be in a state where they cease to provide acceptable levels of service.
The HA framework, including the HAM, uses a simple publish/subscribe mechanism to communicate interesting system events between interested components in the system. By automatically integrating itself into the native networking mechanism (Qnet), this framework transparently extends a local monitoring mechanism to a network-distributed one.
The HAM acts as a conduit through which the rest of the system can both obtain and deliver information regarding the state of the system as a whole. Again, the system could be simply a single node or a collection of nodes connected via Qnet. The HAM can monitor specific processes and can control the behavior of the system when specific components fail and need to be recovered. The HAM also allows external detectors to detect and report interesting events to the system, and can associate actions with the occurrence of those events.
In many HA systems, each single point of failure (SPOF) must be identified and dealt with carefully. Since the HAM maintains information about the health of the system and also provides the basic recovery framework, the HAM itself must never become a SPOF.