There are two possible scenarios where a failover occurs
within Dispatcher High Availability.
In the first scenario, failover occurs due to reach targets. The two
High Availability partners are continually in touch with each other
through heartbeats, and they update one another on how many reach targets
either one of them can ping. If the backup pings more reach targets than
the primary, a failover occurs.
In the second scenario, failover occurs due to a loss of 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, the failover
begins. In this scenario, 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 an High Availability environment and to avoid failover, it
is recommended that you add more than one heartbeat pair.
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