Failover: When two devices are operating as an HA pair, one device is configured as the primary device and the other is configured as the secondary device. The secondary device sends periodic hello messages to the primary device to check whether it is operating. If the primary does not reply, the secondary device retries the connection with the primary for a specified time period. If the secondary device fails to re-establish communication, it determines that the primary system is not functioning as expected, and takes over as the new primary device. This process is known as failover
After a failover, all client connections must be re-established; however, the session persistence rules set before the failover are maintained after a failover.