[Bug] dns_config.domains only works if override_local_dns is enabled

[ajs124]

Is this a support request?

• This is not a support request

Is there an existing issue for this?

• I have searched the existing issues

Current Behavior

Setting dns_config.domains without setting dns_config.override_local_dns = true leads to this warning and dns_config.domains being not applied:
Warning: dns_config.domains is set, but no nameservers are configured. Ignoring domains. (https://github.com/juanfont/headscale/blob/main/hscontrol/types/config.go#L545)

This warning is quite misleading, because nameservers actually refers to resolvers, which is taken from the nameservers field, but only if override_local_dns = true (https://github.com/juanfont/headscale/blob/main/hscontrol/types/config.go#L503).

Expected Behavior

If there are technical reasons, keep this behavior and emit a less misleading error message.

If there aren't any technical reasons for why domains needs override_local_dns, change the check and apply this config.

Steps To Reproduce

Set domains to a non-empty list while setting override_local_dns to false.

Environment

- OS: NixOS 24.05
- Headscale version: master, e.g. 5f9c26930ce796284a8fc7ad167f76e187813d64
- Tailscale version: 1.66.4

Runtime environment

• Headscale is behind a (reverse) proxy
• Headscale runs in a container

Anything else?

I'm open to implementing either option (better error message or changing the check) and opening a PR, if you want me to.

[kradalby]

I think this is a longstanding bug, I dont think the error makes sense based on Tailscales docs, can you give #1987 a go?

[ajs124]

Thanks! I will give that PR a go, but it might take some days/weeks.

[ajs124]

I gave it a try and it seems to solve my problem. Didn't do any extensive tests though.