Erroneously filtering out non-local IPv6 DNS servers when using user-defined networks #46968
Description
Description
I'm having an issue with docker and IPv6 nameservers when using user-defined networks. As is well-known, when using both IPv4 and IPv6 nameservers, musl-based containers can have issues looking up hostnames due to a race looking up hostnames using both nameservers and using the first response. This manifests on my set-up where I'm trying to resolve a local domain name, which fails when done using the default Google DNS servers as set-up by docker.
The documentation states that Google DNS servers are only used with user-defined networks when the host's resolve.conf does not provide any non-local nameservers. My resolve.conf does, however, and I think that docker is erroneously filtering out my IPv6 nameserver:
❯ resolvectl | cat
Global
Protocols: +LLMNR +mDNS -DNSOverTLS DNSSEC=no/unsupported
resolv.conf mode: stub
Link 2 (enp89s0)
Current Scopes: DNS LLMNR/IPv4 LLMNR/IPv6
Protocols: +DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 192.168.0.2
DNS Servers: 192.168.0.2 fe80::ba27:ebff:fe58:5993
Note how I'm using systemd-resolved, however, that doesn't seem to be an issue for Docker when using the default network:
❯ docker run debian cat /etc/resolv.conf
nameserver 192.168.0.2
nameserver fe80::ba27:ebff:fe58:5993%2
When using docker with a user-define network, however, things go wrong and my fe80 nameserver is replaced by Google DNS servers:
❯ docker run --network web debian cat /etc/resolv.conf
nameserver 127.0.0.11
nameserver 2001:4860:4860::8888
nameserver 2001:4860:4860::8844
options edns0 trust-ad ndots:0
Because of the Google DNS servers there, resolving *.localdomain hostnames often fails on musl.
Reproduce
Included in description.
Expected behavior
No response
docker version
Client: Docker Engine - Community
Version: 24.0.7
API version: 1.43
Go version: go1.20.10
Git commit: afdd53b
Built: Thu Oct 26 09:08:02 2023
OS/Arch: linux/amd64
Context: default
Server: Docker Engine - Community
Engine:
Version: 24.0.7
API version: 1.43 (minimum version 1.12)
Go version: go1.20.10
Git commit: 311b9ff
Built: Thu Oct 26 09:08:02 2023
OS/Arch: linux/amd64
Experimental: false
containerd:
Version: 1.6.26
GitCommit: 3dd1e886e55dd695541fdcd67420c2888645a495
runc:
Version: 1.1.10
GitCommit: v1.1.10-0-g18a0cb0
docker-init:
Version: 0.19.0
GitCommit: de40ad0docker info
Client: Docker Engine - Community
Version: 24.0.7
Context: default
Debug Mode: false
Server:
Containers: 27
Running: 27
Paused: 0
Stopped: 0
Images: 109
Server Version: 24.0.7
Storage Driver: btrfs
Btrfs:
Logging Driver: syslog
Cgroup Driver: systemd
Cgroup Version: 2
Plugins:
Volume: local
Network: bridge host ipvlan macvlan null overlay
Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
Swarm: inactive
Runtimes: io.containerd.runc.v2 runc
Default Runtime: runc
Init Binary: docker-init
containerd version: 3dd1e886e55dd695541fdcd67420c2888645a495
runc version: v1.1.10-0-g18a0cb0
init version: de40ad0
Security Options:
apparmor
seccomp
Profile: builtin
cgroupns
Kernel Version: 6.1.0-16-amd64
Operating System: Debian GNU/Linux 12 (bookworm)
OSType: linux
Architecture: x86_64
CPUs: 8
Total Memory: 30.85GiB
Name: sagittarius
ID: SYST:ZGOX:264T:44KN:XQGE:BJIQ:3FGI:ZVOF:VRG3:GCYP:QEIY:EP5Q
Docker Root Dir: /var/lib/docker
Debug Mode: false
Experimental: false
Insecure Registries:
127.0.0.0/8
Live Restore Enabled: falseAdditional Info
No response