[RFE] resolved: add support for looking up arbitrary RRs in locally defined zone files

[nefethael]

Hi,

Is your feature request related to a problem? Please describe.
In embedded system built by Yocto, I'm trying to ease provisioning by limiting specific configuration. In that context, I wish I could access to "some-remote-device" everywhere, instead of real hostname, then I would like to set it only once.

Describe the solution you'd like
Would it be possible for systemd-resolved to create local cname entry?

Describe alternatives you've considered
I know aliasing is possible with /etc/hosts but only by providing static IP, so if the real hostname device uses DHCP, it will fail.
I could also add dnsmasq, but in my case, I use netplan systemd generator for DNS, so it will break too.

Best regards,
Vincent

[gdamjan]

Can we outline a plan for this feature, and I might try implementing it.

Would a list of sub-commands like resolvectl dns-alias add/del/list be sufficient?

something like resolvectl dns-alias add my-alias.example.net 1.1.1.1/www.example.net?

[nefethael]

@gdamjan Hi,

Maybe adding [Alias] section in /etc/systemd/resolved.conf file with something like:

[Alias]
Host1=192.168.1.1
Host2=.... 

Thanks for your effort,

Best regards,
Vincent

[poettering]

I think such explicit support for aliases is a bit too explicit for my taste. I think a more generic approach might be better: let's maybe define a dir where people can drop in DNS zone-file-like files that we read and whose contents we honour preferably over whatever DNS might actually resolve things to. i.e. a bit like /etc/hosts, but for more than A/AAAA. Let's say /etc/systemd/rr/*.rr or so, which we parse line by line, and that takes precedence over everything else. Adding an alias would then be a matter of:

echo "foo.bar. IN CNAME quux." > /etc/systemd/rr/30-myalias.rr

You get the idea.

Of course, the usual overriding logic should apply.

[andrevmatos]

A case where this would be very useful is with containers; with DNSStubListenerExtra, it's already quite feasible to have host's resolved instance serving DNS requests also on veth/local interfaces, and having a way (maybe either/both on /etc and /run) to drop aliases files, would make it easy to make e.g. podman set container's aliases which could work both for host and other containers (in case they're allowed to communicate with them, of course, by firewall).

[poettering]

Actually, this is a duplicate of #17791