kind get kubeconfig --internal no longer produce a kubeconfig with internal server ipaddress

[mikeshng]

What happened:
In kind v0.7.0, I can create a cluster and get the kubeconfig with the --internal flag and produce a kubeconfig with a server field that is pingable. ie: server: https://172.17.0.2:6443
In later version kind v0.8.0 and kind v0.9.0, the kubeconfig that --internal flag produces contains a hostname that is not pingable locally. ie: server: https://kind-control-plane:6443

What you expected to happen:
I expect it behaves like the v0.7.0 version where the server field contains a valid ip.

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

1. download and install the latest (v0.9.0)
2. kind create cluster

$ kind get kubeconfig --internal | grep server
server: https://kind-control-plane:6443

Environment:

• kind version: (use kind version):

kind v0.9.0 go1.15.2 linux/amd64

• Kubernetes version: (use kubectl version):

$ kubectl version
Client Version: version.Info{Major:"1", Minor:"18", GitVersion:"v1.18.2", GitCommit:"52c56ce7a8272c798dbc29846288d7cd9fbae032", GitTreeState:"clean", BuildDate:"2020-04-16T11:56:40Z", GoVersion:"go1.13.9", Compiler:"gc", Platform:"linux/amd64"}
Server Version: version.Info{Major:"1", Minor:"17", GitVersion:"v1.17.0", GitCommit:"70132b0f130acc0bed193d9ba59dd186f0e634cf", GitTreeState:"clean", BuildDate:"2020-01-14T00:09:19Z", GoVersion:"go1.13.4", Compiler:"gc", Platform:"linux/amd64"}

• Docker version: (use docker info):

Server:
 Containers: 85
  Running: 2
  Paused: 0
  Stopped: 83
 Images: 801
 Server Version: 19.03.6

• OS (e.g. from /etc/os-release):

$ cat /etc/os-release 
NAME="Ubuntu"
VERSION="20.04.1 LTS (Focal Fossa)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 20.04.1 LTS"
VERSION_ID="20.04"
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=focal
UBUNTU_CODENAME=focal

[BenTheElder]

Please search the tracker before filing bugs.

#1558

As kind is alpha and the versions are prerelease, behavior can and will change between versions. In this case it was necessary to make major fixes to networking.

[BenTheElder]

Also: internal is for use internal to the docker network, in this context the hostname will work.

If you try to use it externally, it's not supported.