I'm probably being an idiot but I can't for the life of me find the manual failover option in the web GUI.
The manual says "you can force a failover at System Operations -> Force Failover."
I've checked under system operations on both the hosts and VMs and that option is nowhere to be found. I've tried both the authentic theme and the old webmin theme. Refreshed the session and logged out/in.
I've set up the failover group with two host machines and a single VM to be manually failed over. The VM is running on a glusterfs brick mounted on both machines.