Updating the SD-WAN software on an HA pair causes a failover at one point during the update.
Note: Clicking the Update button terminates all open TCP connections.
To update the software on an HA pair
Log on to both appliances.
On the secondary appliance, update the software and reboot. After the reboot, the appliance is still the secondary. Verify that the installation succeeded. The primary appliance should show that the secondary appliance exists but that automatic parameter synchronization is not working, due to a version mismatch.
On the primary appliance, update the software, and then reboot. The reboot causes a failover, and the secondary appliance becomes the primary. When the reboot is completed, HA should become fully established, because both appliances are running the same software.