Active-passive HA cluster does not switch to the backup unit after a failure.

If an individual service has failed that does not disrupt the HA heartbeat, an active-passive HA cluster may not fail over. For example, it is possible that one or more services (such as SMTP, IMAP, POP3, web access, or a hard drive or network interface) could fail on the primary unit (master) without affecting the HA heartbeat.

To cause failover when an individual service fails, configure service monitoring (see “Configuring service-based failover”) on both the primary unit and backup unit.