Allow adding static names to hostresolver

[jandubois]

This is an alternative to adding static names to /etc/hosts on the host, to make them available inside containers running in the guest. In addition this change allows creating aliases to host.lima.internal to point to the host gateway from inside the guest.

Manual testing with examples/docker.yaml with these changes:

hostResolver:
  hosts:
    host.docker.internal: host.lima.internal
    cname.docker.internal: host.docker.internal
    guest.internal: 127.1.1.1

Testing inside an Alpine container running on Docker:

$ docker context create lima --docker "host=unix:///Users/jan/.lima/docker/sock/docker.sock"
$ docker context use lima
$ docker run -it --rm alpine
/ # nslookup host.docker.internal
Server:		10.0.2.3
Address:	10.0.2.3:53

Non-authoritative answer:

Non-authoritative answer:
host.docker.internal	canonical name = host.lima.internal
Name:	host.lima.internal
Address: 192.168.5.2

/ # nslookup cname.docker.internal
Server:		10.0.2.3
Address:	10.0.2.3:53

Non-authoritative answer:

Non-authoritative answer:
cname.docker.internal	canonical name = host.lima.internal
Name:	host.lima.internal
Address: 192.168.5.2

/ # nslookup guest.internal
Server:		10.0.2.3
Address:	10.0.2.3:53

Non-authoritative answer:
Name:	guest.internal
Address: 127.1.1.1

Non-authoritative answer:

In addition this PR contains a bugfix for the hostResolver.ipv6: false configuration: instead of forwarding AAAA queries to the default resolvers, we now return an empty reply to avoid returning NXDOMAIN. During testing I found that that was causing names to resolve correctly on Alpine even when dig and nslookup seemed to show proper DNS information. It might be a bug in the musl resolver.

Finally this PR also adds the current hostname with the slirp IP address to the host resolver. This is done automatically by systemd-resolved, but necessary for e.g. Alpine.

Fixes #622

[AkihiroSuda]

Seems accidentally containing #643

Could you try rebasing with the master?

[jandubois]

Could you try rebasing with the master?

Should be already fixed; maybe you need to refresh?

[jandubois]

Sorry, I did one more force-push to change the hostname address from 127.0.1.1 to 192.168.5.15 (the slirp IP address). This seems to be more in line with the Debian hostname resolution documentation, given that the slirp IP is pretty permanent:

The IP address 127.0.1.1 in the second line of this example may not be found on some other Unix-like systems. The Debian Installer creates this entry for a system without a permanent IP address as a workaround for some software (e.g., GNOME) as documented in the bug #719621.

[AkihiroSuda]

Can we split this yaml to another PR and hold it until right before the release of vNext, to avoid seeing “this example does not work” issues?

[jandubois]

I've restored the original script because I realized it is still required when hostResolver.enabled is false.

I've added comments to the file that should make it obvious that this feature requires lima 0.8.3 or later.

I've also added tests to the PR.

[AkihiroSuda]

Thanks

[jandubois]

@abiosoft You may want to look at the changes to examples/docker.yaml and copy the hostResolver.hosts setting. It will be ignored in older versions of lima, but with 0.8.3 it will make sure that host.docker.internal can be resolved inside containers as well.