Docker DNS server returns NXDOMAIN for SRV records #2574
Description
Docker's internal DNS server doesn't appear to function properly when attempting to resolve SRV records. A lookup like dig -t srv _imaps._tcp.gmail.com works fine on the host system, but returns NXDOMAIN inside a container.
Steps to reproduce:
# Regular rootless docker install:
sudo su -
apt-get install -y uidmap curl
# ... check /etc/subuid for proper entries ...
exit
curl -fsSL https://get.docker.com/rootless | sh
export PATH=${HOME}/bin:$PATH
export DOCKER_HOST=unix:///run/user/$(id -nu)/docker.sock
SRV lookup inside a container:
docker pull debian:buster # or ubuntu:latest, or etc...
docker run --rm -it debian:buster bash -c 'apt-get update && apt-get install -y dnsutils && dig -t srv _imaps._tcp.gmail.com'
System info:
$ docker version
Client: Docker Engine - Community
Version: 19.03.12
API version: 1.40
Go version: go1.13.10
Git commit: 48a66213fe
Built: Mon Jun 22 15:42:53 2020
OS/Arch: linux/amd64
Experimental: false
Server: Docker Engine - Community
Engine:
Version: 19.03.12
API version: 1.40 (minimum version 1.12)
Go version: go1.13.10
Git commit: 48a66213fe
Built: Mon Jun 22 15:49:35 2020
OS/Arch: linux/amd64
Experimental: true
containerd:
Version: v1.2.13
GitCommit: 7ad184331fa3e55e52b890ea95e65ba581ae3429
runc:
Version: 1.0.0-rc10
GitCommit: dc9208a3303feef5b3839f4323d9beb36df0a9dd
docker-init:
Version: 0.18.0
GitCommit: fec3683
$ docker info
Client:
Debug Mode: false
Server:
Containers: 0
Running: 0
Paused: 0
Stopped: 0
Images: 3
Server Version: 19.03.12
Storage Driver: overlay2
Backing Filesystem: extfs
Supports d_type: true
Native Overlay Diff: false
Logging Driver: json-file
Cgroup Driver: none
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: runc
Default Runtime: runc
Init Binary: docker-init
containerd version: 7ad184331fa3e55e52b890ea95e65ba581ae3429
runc version: dc9208a3303feef5b3839f4323d9beb36df0a9dd
init version: fec3683
Security Options:
seccomp
Profile: default
rootless
Kernel Version: 5.3.0-51-generic
Operating System: Ubuntu 19.10
OSType: linux
Architecture: x86_64
CPUs: 4
Total Memory: 8.062GiB
Name: testsystem
ID: 7J5I:IG4C:QNFY:BOTC:E3QP:SH67:FTTP:EA4Z:UKJL:OK4N:XBU5:7PQT
Docker Root Dir: /home/user/.local/share/docker
Debug Mode: false
Registry: https://index.docker.io/v1/
Labels:
Experimental: true
Insecure Registries:
127.0.0.0/8
Live Restore Enabled: false
Product License: Community Engine
WARNING: No swap limit support
WARNING: bridge-nf-call-iptables is disabled
WARNING: bridge-nf-call-ip6tables is disabled