Two identical hardware devices (e.g., two Raspberry Pi units) always synchronized with each other, where one acts as the primary and the other as the secondary.
In case of a failure on the primary, the secondary automatically takes over.
Our homes are now heavily reliant on HA, and even a minimal interruption causes significant inconveniences but, most importantly, insults and humiliation from our partners.
A similar feature is available in the new UDM Pro Max and is called shadow mode.
Thaks!