No DNS Search Domain support in Alpine Linux image due to muslc

[Mickael-van-der-Beek]

It seems like dns.lookup() calls will not work in Node.js's Alpine Linux image versions when search domains are used.

Calls like dns.resolve() won't work for a different reason which is C-Ares having issues with the feature.

Alpine Linux uses musl libc instead of gnu libc, the former didn't support search domains until version 1.1.13. It seems though that even on more recent versions of musl libc, the bug persists.

cf: https://wiki.musl-libc.org/functional-differences-from-glibc.html#Name_Resolver_.2F_DNS
cf: gliderlabs/docker-alpine#8

To make reproduction of this issue easier, I created a repository with one Debian and one Alpine Dockerfile that you can find here:

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

Edit: Might also be related to mhart/alpine-node#107

[SimenB]

Is this actionable for us? Or is it a bug with node and musl?

[LaurentGoderre]

Perhaps not but this kind of issue should be tracked for a case to the broader node community for official support of Alpine Linux.

[bnoordhuis]

See nodejs/node#17850. I'd say this can be closed because it's not an issue with alpine, musl or docker - dns.lookup() dns.resolve() simply does not support search domains at the moment.

[Mickael-van-der-Beek]

@bnoordhuis If you look at the Node.js DNS test repository I created, lookup does work and resolve doesn't:

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

If you then run the syscall in C directly, you will see that there is in fact a difference between Debian and Alpine Linux for the same source code:

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

[bnoordhuis]

Sorry, typo in my comment - I meant dns.resolve(), not dns.lookup().

If you then run the syscall in C directly, you will see that there is in fact a difference between Debian and Alpine Linux for the same source code

Can you summarize the differences?

[Mickael-van-der-Beek]

If you do a getaddrinfo() call with google and use the Belgian TLD be as the search domain, we get 216.58.214.35 for Debian and code -2 (verbose error: Name does not resolve) for Alpine Linux.

If we inspect both containers, the docker compose utility sets up this /etc/resolv.conf file:

# cat /etc/resolv.conf
search be
nameserver 127.0.0.11
options ndots:0

Which looks fine.

The only difference is that in the Debian case we use:

ldd (Debian GLIBC 2.24-11+deb9u1) 2.24

and in the Alpine Linux case:

musl libc (x86_64) Version 1.1.18

From the issue thread below, you can see that the feature was supposedly implemented in muslc@1.1.13 but even in edge versions of Alpine Linux which come with more recent versions of muslc, the problem still exists:

gliderlabs/docker-alpine#8

In that sense it's not a Node.js issue, just an Alpine Linux issue but it's still interesting to document the issue for posterity.

[Mickael-van-der-Beek]

@bnoordhuis Just to clarify, the issue I described above is valid for the dns.lookup() call and the ticket I opened on the main Node.js repository is about the language not using the C-Ares that supports DNS search domains in the dns.resolve() call.

[bnoordhuis]

Ah, I get it now. That's a documented difference with glibc: musl ignores search/domain for names with dots >= ndots. Since 0 >= 0, it's always going to do a regular lookup.

With ndots:1, musl and glibc behave the same for a bareword domain name (but not for e.g. domain.tld because that requires ndots:2.)

Is that options ndots:0 a docker default? I don't believe our docker image sets that.

[Mickael-van-der-Beek]

@bnoordhuis That seems to indeed be the default value in Docker based on libnetwork:

https://github.com/docker/libnetwork/blob/19ac3ea7f52bb46e0eb10669756cdae0c441a5b1/resolver.go#L204

[Labutin]

FYI: https://forums.docker.com/t/resolved-service-name-resolution-broken-on-alpine-and-docker-1-11-1-cs1/19307

[CoreyCole]

I'm trying to make requests from an alpine node container to another container and running into dns issue ENOTFOUND. Is this related to this issue?

https://stackoverflow.com/questions/50263684/docker-compose-networking-with-axios-node-error-enotfound

[CoreyCole]

I get the same ENOTFOUND error that I get in node:8.11-alpine when I switch to node:8.11, so my issue is probably unrelated

[chorrell]

Closing as an Alpine/Docker issue