You can add a FortiGate HA cluster using the Add Model Device method when adding a new device. The process of adding a FortiGate HA cluster is similar to adding a model device using FortiGate serial numbers. See Adding a model device by serial number in the FortiManager Administration Guide.
You can add the two FortiGate devices as model devices to be part of the HA cluster. In the Add Device dialog, select Add Model Device, and select the HA Cluster option. Populate the mandatory fields HA Mode, Serial Number for both the nodes, Device Model type, Group Name and Password for the HA cluster, Node 1 and Node 2 priority, Monitor Interface members, and Heartbeat Interface members.
The FortiGate device with a higher node priority will be considered as the primary device of the HA cluster.
Both the FortiGate devices to be added to the HA cluster must be on the same firmware version. If not, the devices will be enforced with the same version as selected in the Enforce Firmware Version field in the Add Device dialog.
FortiManager adds both the FortiGate devices as model devices and creates an HA cluster. Based on device node priorities, both the devices will come online and show up in FortiManager one after the other. You can view the status of the HA cluster and information about each of the nodes of the HA cluster in Device Manager.
You can also edit the HA cluster information after adding it. Use the Edit Device screen to modify the HA cluster information by modifying the fields IP Address, Admin User and Password, Cluster Members, Enforce Firmware Version, System Template, and Policy Package.