@kanga_who: Thanks for the clarification, sorry if I was misinterpreting anything
@krisjanis2000: To clarify - are you having a general Ubuntu 20.04 DNS setup issue, or something with HA Supervised internal DNS setup?
I wish I had documented it better when I did it, but poking through my command history… it basically revolves around systemd.resolved & the whole local caching DNS setup in Ubuntu 20.04 server is kind of a complicated mess and wasn’t working for me at first. Basically DNS uses a local server @ 127.0.0.53 as a cache, which then is supposed to use the DHCP configured server.
Try “nslookup HOSTNAME” and see what server it uses (and see if DNS worked). Then try “nslookup HOSTNAME REALDNS_IP”
In the end I tried a few things, including effectively disabling the systemd.resolved proxy by mesing with some configs and symlinking /etc/resolv.conf from /run/systemd/resolve/resolv.conf instead of resolv-stub.conf. Then I installed network-manager (which the docs say is highly recommended for HA Supervised) - and disabled the ModemManager and wpa_supplicant services since I am using Ethernet.
But: I now see after updating the OS and rebooting the device the symlink I changed is reverted and the proxy is being used again! (I assume some package update overwoite my changes, oh well). And of course it’s now all working fine… so I’m not sure how helpful all of the above is, but maybe something can point you in the right direction.
Hmm - one more possibility is I also added an internal domain name on my router’s DNS so clients would get it via DHCP. I think there was some issue with search path but can’t say for sure (in case your issue is DNS resolution of other local machines on your network).