If the master control panel is hosted on a public cloud instance like at OVH, there is little chance of an outage. I've had instances running there for several years and never noticed any downtime. Only once did the monitor notify me that the server was not responding, but it looked like the datacentre automatically migrated the instance to a different host. The instance was back online after a few minutes.
Then, for Email and DNS (these need the best uptime, especially email), hosting them on a public cloud instance with HA, just like with the control panel is best.
Then, for the websites/apps themselves, it is best to use the fastest dedicated servers. Sure, there can be an issue, but Enhance allows for the quick decommission of a dead server and restores the backups from a different backup server. It should be speedy as long as the production server hosting the websites/apps and backup servers have 10Gb/s connections. The restoration should be much faster.
I think that's the best way to do it. There's no need to mess about with custom HA then. That said, if Enhance could have HA built-in and it worked well, it would be a nice addition. Though HA can be costly and complex, too. Catch 22. Pros and cons.
