Merge pull request #35843 from bulletRush/feature/pre-hostname-check

Automatic merge from submit-queue

[kubeadm] pre-flight check hostname to ensure kubelet can launch static pods li…

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**What this PR does / why we need it**: pre-flight check hostname to ensure kubelet can launch static pods like kube-apiserver/kube-controller-manager

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes # 

**Special notes for your reviewer**:

# what is the influence of this issue?

kubelet will not create api server and kcm pod if your hostname is uncorrect. It complain the config files in "/etc/kubernetes/manifests" are invlid.

# how to reproduce this issue?

change your hostname by `hostnamectl set-hostname vm_81_12_centos`. then run `kubeadm init`. you will get this error log from kubelet:

```log
Oct 27 11:12:57 vm_81_12_centos kubelet: I1027 11:12:57.279458    2695 file.go:123] Can't process config file "/etc/kubernetes/manifests/kube-controller-manager.json": invalid pod: [metadata.name: Invalid value: "kube-controller-manager-vm_81_12_centos": must match the regex [a-z0-9]([-a-z0-9]*[a-z0-9])?(\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)* (e.g. 'example.com') spec.nodeName: Invalid value: "vm_81_12_centos": must match the regex [a-z0-9]([-a-z0-9]*[a-z0-9])?(\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)* (e.g. 'example.com')]
```

# where the error comes from in the code?

`pkg/kubelet/config/file.go:144 sourceFile:extractFromDir`

```go
func (s *sourceFile) extractFromDir(name string) ([]*api.Pod, error) {
	dirents, err := filepath.Glob(filepath.Join(name, "[^.]*"))
	if err != nil {
		return nil, fmt.Errorf("glob failed: %v", err)
	}

	pods := make([]*api.Pod, 0)
	if len(dirents) == 0 {
		return pods, nil
	}

	sort.Strings(dirents)
	for _, path := range dirents {
		statInfo, err := os.Stat(path)
		if err != nil {
			glog.V(1).Infof("Can't get metadata for %q: %v", path, err)
			continue
		}

		switch {
		case statInfo.Mode().IsDir():
			glog.V(1).Infof("Not recursing into config path %q", path)
		case statInfo.Mode().IsRegular():
			pod, err := s.extractFromFile(path)
			if err != nil {
-->				glog.V(1).Infof("Can't process config file %q: %v", path, err)
			} else {
				pods = append(pods, pod)
			}
		default:
			glog.V(1).Infof("Config path %q is not a directory or file: %v", path, statInfo.Mode())
		}
	}
	return pods, nil
}
```

# how to fix it?

1. change hostname by `hostnamectl set-hostname <right host name>` or
2. add `hostnameOverride` config. If hostnameOverride is set, then kubelet will use this value instead of system hostname.

**Release note**:
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…ke kube-apiserver/kube-controller-manager and so on.

cmd/kubeadm/app/preflight/BUILD

@@ -16,6 +16,8 @@ go_library(
     tags = ["automanaged"],
     deps = [
         "//cmd/kubeadm/app/apis/kubeadm:go_default_library",
+        "//pkg/api/validation:go_default_library",
         "//pkg/util/initsystem:go_default_library",
+        "//pkg/util/node:go_default_library",
     ],
 )

cmd/kubeadm/app/preflight/checks.go

@@ -25,7 +25,9 @@ import (
 	"os/exec"
 
 	kubeadmapi "k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm"
+	"k8s.io/kubernetes/pkg/api/validation"
 	"k8s.io/kubernetes/pkg/util/initsystem"
+	"k8s.io/kubernetes/pkg/util/node"
 )
 
 type PreFlightError struct {
@@ -170,10 +172,24 @@ func (ipc InPathCheck) Check() (warnings, errors []error) {
 	return nil, nil
 }
 
+// HostnameCheck checks if hostname match dns sub domain regex.
+// If hostname doesn't match this regex, kubelet will not launch static pods like kube-apiserver/kube-controller-manager and so on.
+type HostnameCheck struct{}
+
+func (hc HostnameCheck) Check() (warnings, errors []error) {
+	errors = []error{}
+	hostname := node.GetHostname("")
+	for _, msg := range validation.ValidateNodeName(hostname, false) {
+		errors = append(errors, fmt.Errorf("hostname \"%s\" %s", hostname, msg))
+	}
+	return nil, errors
+}
+
 func RunInitMasterChecks(cfg *kubeadmapi.MasterConfiguration) error {
 	// TODO: Some of these ports should come from kubeadm config eventually:
 	checks := []PreFlightCheck{
 		IsRootCheck{root: true},
+		HostnameCheck{},
 		ServiceCheck{Service: "kubelet"},
 		ServiceCheck{Service: "docker"},
 		PortOpenCheck{port: int(cfg.API.BindPort)},
@@ -207,6 +223,7 @@ func RunJoinNodeChecks() error {
 	// TODO: Some of these ports should come from kubeadm config eventually:
 	checks := []PreFlightCheck{
 		IsRootCheck{root: true},
+		HostnameCheck{},
 		ServiceCheck{Service: "docker"},
 		ServiceCheck{Service: "kubelet"},
 		PortOpenCheck{port: 10250},