If your HA configuration includes HA interface monitoring, if a primary FortiGate-7000E interface fails or is disconnected while a cluster is operating, a link failure occurs. When a link failure occurs, the FortiGate-7000Es in the cluster negotiate to select a new primary FortiGate-7000E. The link failure means that a that primary FortiGate-7000E with the most link failures will become the secondary and the FortiGate-7000E with the fewest link failures becomes the primary FortiGate-7000E.
Just as for a device failover, the new primary FortiGate-7000E sends gratuitous arp packets out all of its connected interfaces to inform attached switches to send traffic to it. Sessions then resume with the new primary FortiGate-7000E.
If the secondary FortiGate-7000E experiences a link failure, its status in the cluster does not change. However, in future negotiations a FortiGate-7000E with a link failure is less likely to become the primary FortiGate-7000E.
If one of the FortiGate-7000Es experiences an FIM or FPM failure and the other experiences a link failure, the FortiGate-7000E with the most operating FIMs or FPMs becomes the primary FortiGate-7000E, even if it is also experiencing a link failure.