Add config options that allow container DNS to point to localhost

[tonistiigi]

Currently, the localhost nameservers are removed and replaced with default nameservers if needed because it is assumed that internal containers can't access localhost nameservers anyway. But this may not be true if deployment reuses host networking for internal containers by default(that is fine if the whole daemon is already inside a container sandbox). We could add a config option to control this behavior.

ref docker/buildx#1347

[tonistiigi]

buildkit/executor/oci/resolvconf.go

Lines 96 to 99 in b6de3ca

	f, err = resolvconf.FilterResolvDNS(dt, true)
	if err != nil {
	return "", err
	}

should be the specific call that currently removes localhost records.

[ch33hau]

Hi @tonistiigi, can I try to work on this issue?

[tonistiigi]

@ch33hau Sure

[ch33hau]

Hi @tonistiigi,

Now I see how it works and is able to reproduce it.

But I have a few questions before I can proceed.

Am I right that the new config option should be available on docker buildx build, and docker buildx bake can override it with the --set option?

And what should be the option name? I am thinking no-local-dns or remove-local-dns and defaults to true, is that ok?

[tonistiigi]

We might not even require new config option. Just when https://github.com/moby/buildkit/blob/master/cmd/buildkitd/config/config.go#L53 is host the DNS from localhost should work as well.

[ch33hau]

Hi @tonistiigi , I have created a draft PR #3244 with some questions there. Could you please take a look and see if I am on the right track?

Thanks a lot!

[polarathene]

when https://github.com/moby/buildkit/blob/master/cmd/buildkitd/config/config.go#L53 is host

For reference since that wasn't a permalink and line has shifted since:

• Oct 2022:

  buildkit/cmd/buildkitd/config/config.go

  Line 53 in f57dc7f

  Mode string `toml:"networkMode"`

• Sep 2023:

  buildkit/cmd/buildkitd/config/config.go

  Line 70 in 97e0efa

  Mode string `toml:"networkMode"`