I have two PiHole instances plugged on opposite sides of the house. Instead of the mentioned GravitySync, I just occasionally copy the backup file from the primary to the secondary pihole instance (both of which are dockerized on Raspberry Pi hardware)

Works great. Rarely need to think of it. I recommend looking up the recommended whitelist and adding anything there that looks relevant to you.

Last downtime was a month ago when external circumstances forced me to move both servers. Yhe RPi, lacking a real time clock or its neighbor to bootstrap DNS, couldn't get the current time ir dns, and thus had out-of-date certificates for dnssec... Solution was to add the direct ip address to an NTP server temporarily to the list of websites to use for NTP.