How-to: Upgrade a FortiGate HA Cluster

I often get asked how well the FortiGates handle firmware upgrades when they're in a high availability cluster. Clients want to know how the upgrade is handled and if there's any 'gotchas' they should be aware of.

Great news is that for the last few years the HA firmware upgrades are very simple and automated. No more manually breaking, upgrading then rejoining the clustered units each time a firmware upgrade is required.

Unable to change HA mode from Standalone on a FortiGate

Today while setting up two devices in HA I noticed that each time I changed the mode from 'Standalone' to 'Active-Passive' or 'Active-Active', the config would always revert backto 'Standalone' after I applied the change.