[AIX HP-UX Linux Solaris Windows]

Detecting server failures with heartbeats and reach targets

Configure heartbeats and reach targets to detect server failures and control when failovers can occur.

About this task

Besides the basic criteria of failure detection (the loss of connectivity between active and standby Dispatchers, detected through the heartbeat messages), there is another failure detection mechanism named reachability criteria. When you configure the Dispatcher you can provide a list of hosts that each of the Dispatchers should be able to reach in order to work correctly. The two high availability partners continually communicate with each other through heartbeats, and they update one another on how many reach targets either one of them can ping. If the standby pings more reach targets than the active, a failover occurs.

Heartbeats:Heartbeats are sent by the active Dispatcher and are expected to be received by the standby Dispatcher every half second. If the standby Dispatcher fails to receive a heartbeat within 2 seconds, a failover begins. All heartbeats must break for a takeover from the standby Dispatcher to occur. In other words, when two heartbeat pairs are configured, both heartbeats must break. To stabilize a high availability environment and to avoid failover, add more than one heartbeat pair.

Reach target considerations: For reach targets, you should choose at least one host for each subnet your Dispatcher machine uses. The hosts could be routers, IP servers or other types of hosts. Host reachability is obtained by the reach advisor, which pings the host. Failover takes place either if the heartbeat messages cannot go through, or if the reachability criteria are met better by the standby Dispatcher than by the primary Dispatcher. To make the decision based on all available information, the active Dispatcher regularly sends the standby Dispatcher its reachability capabilities. The standby Dispatcher then compares those capabilities with its own and decides whether to switch.
Note: When you configure the reach target, the reach advisor must also be started. The reach advisor starts automatically when you start the manager function. For more information on the reach advisor, see List of advisors.

Procedure




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Scripts to run with high availability
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Last updatedLast updated: Jun 20, 2011 4:04:37 PM EDT
File name: tprf_highfail.html