Good solution to automatically revert to "normal" if Pi Hole dies?

[jfb]

Here is an alternate solution that doesn't require monitoring scripts - have both Pi-Holes serve DHCP on non-overlapping ranges. Clients can get an IP from either Pi-Hole. Set static IPs for the Pi-Hole at some low part of the IP range (<10). Pi1 DHCP range 50-100, Pi2 DHCP range 150-200, for example.

During the DHCP handshake, have each Pi-Hole provide the IP of the opposite Pi-Hole as a second DNS. Each client will now have the DNS for two Pi-Holes. There is no active load-balancing; clients will use either or both Pi-Holes as long as they are both up. If either Pi-Hole fails, the clients move seamlessly to the other.

Secondary DNS Server for DHCP

I have it running in different environments (two of them at an enterprise level, one with more than 100 clients). They all run on Raspberry Pi hardware in various revisions. They never failed so far, so I wouldn't bother too much. A clever idea might be to set up two independent Pi-hole's and (two distinct devices in the same network) and set up those two IPs as "primary" and "secondary" servers. All devices should be able to resolve domains, even if one of them fails for some reason. The cost…