Kind: dns problem in apline based docker image

[WeihanLi]

What happened:

I've had a dns problem, the pod container can not resolve the external network dns like github.com.

There's a similar issue in kubernetes repository https://github.com/kubernetes/kubernetes/issues/64924, but I'm not sure the problem is the same with it.

In my case, it only happened on alpine based image, it works on Debian based image in kind k8s cluster, but it works on docker desktop k8s cluster, so I'm consufed.

What you expected to happen: I think it should resolve the external dns correctly

How to reproduce it (as minimally and precisely as possible):

you can use this Dockerfile to build a image or use weihanli/accountingapp:latest for alpine based image to have a test

Anything else we need to know?:

Environment:

• kind version: (use kind version): 0.2.1

• Kubernetes version: (use kubectl version):

  Client Version: version.Info{Major:"1", Minor:"14", GitVersion:"v1.14.0", GitCommit:"641856db18352033a0d96dbc99153fa3b27298e5", GitTreeState:"clean", BuildDate:"2019-03-25T15:53:57Z", GoVersion:"go1.12.1", Compiler:"gc", Platform:"linux/amd64"}
  Server Version: version.Info{Major:"1", Minor:"13", GitVersion:"v1.13.4", GitCommit:"c27b913fddd1a6c480c229191a087698aa92f0b1", GitTreeState:"clean", BuildDate:"2019-03-20T16:54:39Z", GoVersion:"go1.11.5", Compiler:"gc", Platform:"linux/amd64"}

• Docker version: (use docker info):

  Containers: 1
  Running: 1
  Paused: 0
  Stopped: 0
  Images: 36
  Server Version: 18.06.1-ce
  Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Native Overlay Diff: true
  Logging Driver: json-file
  Cgroup Driver: cgroupfs
  Plugins:
  Volume: local
  Network: bridge host macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file logentries splunk syslog
  Swarm: inactive
  Runtimes: runc
  Default Runtime: runc
  Init Binary: docker-init
  containerd version: 468a545b9edcd5932818eb9de8e72413e616e86e
  runc version: 69663f0bd4b60df09991c08812a60108003fa340
  init version: fec3683
  Security Options:
  seccomp
  Profile: default
  Kernel Version: 5.0.7-050007-generic
  Operating System: Ubuntu 18.04.2 LTS
  OSType: linux
  Architecture: x86_64
  CPUs: 2
  Total Memory: 7.765GiB
  Name: my-ubuntu
  ID: GB5R:7P7A:O4VF:MH5T:NUVS:LQTC:7XGX:FS26:RN6X:32I7:6GGQ:TDNE
  Docker Root Dir: /var/lib/docker
  Debug Mode (client): false
  Debug Mode (server): false
  Registry: https://index.docker.io/v1/
  Labels:
  Experimental: false
  Insecure Registries:
  127.0.0.0/8
  Live Restore Enabled: false

WARNING: No swap limit support

• OS (e.g. from /etc/os-release):

  NAME="Ubuntu"
  VERSION="18.04.2 LTS (Bionic Beaver)"
  ID=ubuntu
  ID_LIKE=debian
  PRETTY_NAME="Ubuntu 18.04.2 LTS"
  VERSION_ID="18.04"
  HOME_URL="https://www.ubuntu.com/"
  SUPPORT_URL="https://help.ubuntu.com/"
  BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
  PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
  VERSION_CODENAME=bionic
  UBUNTU_CODENAME=bionic

[tao12345666333]

I guess this problem has nothing to do with kind, it is probably due to the problem of musl based on alpine image. https://bugs.alpinelinux.org/issues/9017

and you can try to use nslookup to get more detail.

[tao12345666333]

/triage needs-information

[WeihanLi]

nslookup info

[WeihanLi]

should I close this issue for a alpine related issue?

[tao12345666333]

right. please see: https://github.com/gliderlabs/docker-alpine/issues/476

[WeihanLi]

OK, thanks @tao12345666333

[BenTheElder]

You may need https://github.com/kubernetes/kubernetes/commit/4274c426cee6f6d1e42ce194952190c587888e7d if you're using go in your Alpine image.

[BenTheElder]

Or rather: an etc/nsswitch.conf entry. Your Debian image most likely has one.

[BenTheElder]

https://github.com/kubernetes/kubernetes/pull/69238 and https://github.com/kubernetes/kubernetes/issues/69195 have some more discussion. This issue is generic to alpine (non glibc) images with go binaries