how does dns resolution work?

[christhomas]

I have a need to run a dnsmasq container for special application level setup which can be dynamic as part of a local development toolkit. The idea is to run custom domains locally and use a dnsmasq container to resolve them to the local machine.

From what I understand, docker runs it's own dns resolver for special situations where it needs to do a similar thing, resolve things that only matter to the local docker machine and kubernetes does something similar with coredns and resolves it's special internal names.

I think lima also has something similar according to some issues and tickets that I've read, so it makes sense that the container software itself runs it's own private dns for things it needs to resolve. But then how does everything else get resolved? Do all those requests go to the host machine which uses it's own configured dns resolvers to do the rest of the work?

If so, that would mean my setup would work because what I do is set a custom ip address for all domains that I want to cater for and then listen on the host machine's port 53, falling back to the host machines router (the adsl box or whatever the machine is configured with) for any public dns stuff.

So I suppose in this setup, there are three dns resolvers: docker(private docker things), my toolkit(my custom domains), the router(everything else)

Does anybody know how I could get that setup working with lima? maybe the useHostResolver option does exactly this behaviour? Anybody have any advice?

[jandubois]

The hostResolver is a DNS stub resolver that runs on the host, resolves names using the macOS or Linux resolver, and then provides that data to the guest VM via DNS. This is the only nameserver exposed to the VM, so all requests should go through this channel.

So if your local dnsmasq is configured in a way that the host uses it to look up names, then everything should work automatically. Have you tried it? Did it not work?

[christhomas]

I think maybe the problem is that dns is UDP and Lima only supports tcp port forwarding? So my containing can't have the hosts port 53 mapped to it, so no requests for resolving custom domains actually arrive in the dnsmasq container in the first place.

[christhomas]

But just to clarify, this software sets itself up as the first dns resolver for your system and then sets up the following ip addresses for your router dns, etc as the latter fallback addresses. So all dns uses the first available resolver, which is the dnsmasq container, then I've got a docker container mapping port 53 to scoop up requests and upstream all the non-resolved stuff to the google dns servers (I could also use the router ip address too and probably will implement that in a future version.

This works great when using docker but with lima, no dns requests arrive to the container, so I looked around and found the issue with TCP and UDP and I thought maybe that was the problem. Or maybe this issue is old and now UDP is supported?

[stonechen28]

Have you solved the problem? I am facing a similar problem and sometimes it works and sometimes it don't.