No DNS Search Domain support in C-Ares calls

[Mickael-van-der-Beek]

• Version: node:9.2.0-slim (Docker image)
• Platform: Linux 8f48fe466727 4.9.49-moby 1 SMP Fri Dec 8 13:40:02 UTC 2017 x86_64 GNU/Linux
• Subsystem: dns

It would seem that currently, Node.js calls through the C-Ares DNS resolver (resolve4() and resolve6()) don't support search domains.

Is this a bug? If not, are there current or planned configuration options to specify them?
Should this issue be cross-posted to the C-Ares repository?

To make reproduction of this issue easier, I created a Docker-based repository that you can find here:

https://github.com/Mickael-van-der-Beek/node-dns-test

PS: Be careful to not use Alpine Linux as Docker based image due to muslc being used and not glibc. I will create a ticket about this in their repository later.

EDIT: Might be related to this issue that was supposedly fixed in the past: #9799

[bnoordhuis]

This is about node.js not honoring the domain or search attribute in /etc/resolv.conf? That's because we call ares_query(), not ares_search(). ares_query() does not take search domains into account.

ares_search() cannot be the default because it makes up to num_search_domains + 1 queries but we could add a { search: true } option.

[Mickael-van-der-Beek]

@bnoordhuis I see, good to know. Thanks for the quick answer.

The situation we encountered at my company is that we use a VPN to connect to our Kubernetes cluster. Services can have multiple instances and use DNS hostnames to load balance to one or the other (through KubeDNS). We also put these hostnames behind subdomains of one of our domains so that even development services benefit of our TLS certificate.

Since the hostnames are a bit long outside of the Kubernetes internal network, we let the VPN access the Kuberenetes DNS resolver to allow for short-hand service hostnames usage on our development machines.

@bcorijn Correct me if I'm wrong?

Not the most common use case of course, more of a convenience thing. So I understand if this isn't a priority.

It did take us a bit of time to understand why certain apps were affected or not because some DNS resolutions used dns.lookup() which worked fine in this case and others were using dns.resolve() which didn't.

[Manicqin]

Hi, If this issue is still open I can take it.

[bnoordhuis]

@Manicqin You mean adding a search option? Go for it; no one is working on it, AFAIK.

[UtkarshGupta-CS]

@Manicqin will you be able to resolve this issue or can I take up this issue?

[UtkarshGupta-CS]

@bnoordhuis Can I work on this issue?