What keywords did you search in kubeadm issues before filing this one?

• join
• hostname
• lookup
• "no such host"

Is this a BUG REPORT or FEATURE REQUEST?

BUG REPORT

Versions

kubeadm version (use kubeadm version):

• 1.10.2

  kubeadm version: &version.Info{Major:"1", Minor:"10", GitVersion:"v1.10.2", GitCommit:"81753b10df112992bf51bbc2c2f85208aad78335", GitTreeState:"clean", BuildDate:"2018-04-27T09:10:24Z", GoVersion:"go1.9.3", Compiler:"gc", Platform:"linux/amd64"}

• v1.11.0-alpha.2 .

  kubeadm version: &version.Info{Major:"1", Minor:"11+", GitVersion:"v1.11.0-alpha.2", GitCommit:"ed9b25c90241b2b8a1fa10b96381c57f99ca952a", GitTreeState:"clean", BuildDate:"2018-05-02T12:02:56Z", GoVersion:"go1.10.1", Compiler:"gc", Platform:"linux/amd64"}

Environment:

• Kubernetes version (use kubectl version):

Client Version: version.Info{Major:"1", Minor:"10", GitVersion:"v1.10.2", GitCommit:"81753b10df112992bf51bbc2c2f85208aad78335", GitTreeState:"clean", BuildDate:"2018-04-27T09:22:21Z", GoVersion:"go1.9.3", Compiler:"gc", Platform:"linux/amd64"}

Server Version: version.Info{Major:"1", Minor:"10", GitVersion:"v1.10.2", GitCommit:"81753b10df112992bf51bbc2c2f85208aad78335", GitTreeState:"clean", BuildDate:"2018-04-27T09:10:24Z", GoVersion:"go1.9.3", Compiler:"gc", Platform:"linux/amd64"}

• Cloud provider or hardware configuration:

AWS EC2 instance, but no Kubernetes cloud provider installed or activated.

• OS (e.g. from /etc/os-release):

NAME="Container Linux by CoreOS"
ID=coreos
VERSION=1688.5.3
VERSION_ID=1688.5.3
BUILD_ID=2018-04-03-0547
PRETTY_NAME="Container Linux by CoreOS 1688.5.3 (Rhyolite)"
ANSI_COLOR="38;5;75"
HOME_URL="https://coreos.com/"
BUG_REPORT_URL="https://issues.coreos.com"
COREOS_BOARD="amd64-usr"

• Kernel (e.g. uname -a):

Linux ip-10-103-0-183 4.14.32-coreos #1 SMP Tue Apr 3 05:21:26 UTC 2018 x86_64 Intel(R) Xeon(R) Platinum 8175M CPU @ 2.50GHz GenuineIntel GNU/Linux

• Others:

My /etc/hosts file has only the following two entries:

127.0.0.1       localhost
::1             localhost

What happened?

When running kubeadm join (with the --config flag, at least), it fails to detect my machine's hostname, and the "Hostname" pre-flight check fails:

$ sudo kubeadm-alpha join --config ./node-config.yaml 
W0517 17:47:19.298833    2556 flags.go:39] log_backtrace_at is DEPRECATED and will be removed in a future version. Use log-backtrace-at instead.
W0517 17:47:19.299530    2556 flags.go:39] log_backtrace_at is DEPRECATED and will be removed in a future version. Use log-backtrace-at instead.
W0517 17:47:19.299535    2556 flags.go:39] log_dir is DEPRECATED and will be removed in a future version. Use log-dir instead.
W0517 17:47:19.299541    2556 flags.go:39] log_dir is DEPRECATED and will be removed in a future version. Use log-dir instead.
I0517 17:47:19.300854    2556 join.go:228] [preflight] running pre-flight checks
	[WARNING FileExisting-crictl]: crictl not found in system path
Suggestion: go get github.com/kubernetes-incubator/cri-tools/cmd/crictl
I0517 17:47:19.321199    2556 kernel_validator.go:81] Validating kernel version
I0517 17:47:19.321257    2556 kernel_validator.go:96] Validating kernel config
	[WARNING SystemVerification]: docker version is greater than the most recently validated version. Docker version: 17.12.1-ce. Max validated version: 17.03
	[WARNING Hostname]: hostname "" could not be reached
	[WARNING Hostname]: hostname "" lookup : no such host
[preflight] Some fatal errors occurred:
	[ERROR Hostname]: hostname "" a DNS-1123 subdomain must consist of lower case alphanumeric characters, '-' or '.', and must start and end with an alphanumeric character (e.g. 'example.com', regex used for validation is '[a-z0-9]([-a-z0-9]*[a-z0-9])?(\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*')
[preflight] If you know what you are doing, you can make a check non-fatal with `--ignore-preflight-errors=...`

Note, though, that my machine has a hostname, though it's not registered with DNS:

$ hostname
ip-10-103-0-183

$ nslookup ip-10-103-0-183
Server:		10.103.0.130
Address:	10.103.0.130#53

Non-authoritative answer:
Name:	ip-10-103-0-183.ec2.internal
Address: 10.103.0.183

What you expected to happen?

kubeadm join should have detected my machine's hostname and carried on without complaint.

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

To match my scenario,

• Run an AWS EC2 instance that's not yet part of this Kubernetes cluster.
• Create files node-config.yaml:
  (This may be immaterial.)

apiVersion: kubeadm.k8s.io/v1alpha1
kind: NodeConfiguration
tlsBootstrapToken: 4d4c4k.6u9tj98fukd68f8c
discoveryFile: /etc/kubernetes/kubeadm/discovery.yaml

• Create file discovery.yaml:
  (This may be immaterial.)

apiVersion: v1
clusters:
- cluster:
    certificate-authority-data: <base64-encoded CA certificate bundle>
    server: <API server endpoint>
  name: ""
contexts: []
current-context: ""
kind: Config
preferences: {}
users: []

• Run the following command:
  kubeadm join --config node-config.yaml
• Observe that the "Hostname" pre-flight check complains about the hostname being empty.

Anything else we need to know?

It's possible to work around this problem by skipping the "Hostname" pre-flight check.

I first mentioned this problem in the long-closed kubernetes/kubernetes#49065. @erikh has ideas for what still be wrong here.