You can set up firewall rules to redirect the traffic destined for public DNS servers to your internal DNS server.

Not sure how to construct that rule in the unifi firewall but it comes down to “any outbound traffic on port 53 that’s not destined for the adguard server, redirect it.”

I just use ssh for management. Monitoring is handled by nagios.

Shouldn’t use the Xfinity router anyway, that thing is fuckin garbage.

I really hope you have that backed up