Having just experienced a SDcard failure during the night I woke up to a very cold house. It was 4 degrees outside, and not much warmer inside, I needed it back up and running fast. Additionally, I could not turn on any lights to see what I was doing.
I had to rebuild/restore HA on a RPI. Whilst I did this my entire house automation was down - including the heating. Since an HA instance is central to the function of the house the lack of a standby instance makes this a critical single point of failure, with serious consequences.
Is it possible to have a second HA instance running alongside the primary instance that can take over control when the primary goes off-line? The secondary instance could simply monitor the primary every minute, and if there is no response after 3 consecutive attempts, then the secondary will take over. Control can be transferred back to the primary when it comes on-line again. All configuration work will be done on the primary and copied to the secondary. There is no need to make changes to the secondary.