To configure HA options go to System Settings > General > HA. From here you can configure FortiManager units to start an HA cluster or you can change the HA configuration of the cluster.

To configure a cluster, you must set the mode of the primary unit to Master and the modes of the backup units to Slave.

Then you must add the IP addresses and serial numbers of each backup unit to primary unit peer list. The IP address and serial number of the primary unit must be added to each of the backup unit HA configurations. Also, the primary unit and all backup units must have the same Cluster ID and Group Password.

You can connect to the primary unit Web‑based Manager to work with FortiManager. Because of configuration synchronization you can configure and work with the cluster in the same way as you would work with a standalone FortiManager unit.

When the cluster is operating, from the primary unit Web‑based Manager you can change HA settings. For example you might want to change the heartbeat interval and failover threshold to fine tune the failure detection time. You should also change the password and Cluster ID to be different from the default settings.