Merge pull request #49825 from erhudy/bugfix/kubeadm-337-empty-node-name

Automatic merge from submit-queue

Fixes kubernetes/kubeadm#347: empty node name when joining nodes with kubeadm

Node name discovery failed on `kubeadm join`. If a node name
is not explicitly provided, it will be looked up.

**What this PR does / why we need it**: `kubeadm join` fails because the preflight checks always see an empty node name. This corrects that issue.

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes kubernetes/kubeadm#347

**Special notes for your reviewer**:

**Release note**:

```release-note
kubeadm: Fix join preflight check false negative
```

cmd/kubeadm/app/cmd/BUILD

@@ -45,6 +45,7 @@ go_library(
         "//pkg/printers:go_default_library",
         "//pkg/util/i18n:go_default_library",
         "//pkg/util/initsystem:go_default_library",
+        "//pkg/util/node:go_default_library",
         "//pkg/util/version:go_default_library",
         "//pkg/version:go_default_library",
         "//vendor/github.com/ghodss/yaml:go_default_library",

cmd/kubeadm/app/cmd/join.go

@@ -36,6 +36,7 @@ import (
 	kubeadmutil "k8s.io/kubernetes/cmd/kubeadm/app/util"
 	kubeconfigutil "k8s.io/kubernetes/cmd/kubeadm/app/util/kubeconfig"
 	"k8s.io/kubernetes/pkg/api"
+	nodeutil "k8s.io/kubernetes/pkg/util/node"
 )
 
 var (
@@ -135,6 +136,10 @@ type Join struct {
 func NewJoin(cfgPath string, args []string, cfg *kubeadmapi.NodeConfiguration, skipPreFlight bool) (*Join, error) {
 	fmt.Println("[kubeadm] WARNING: kubeadm is in beta, please do not use it for production clusters.")
 
+	if cfg.NodeName == "" {
+		cfg.NodeName = nodeutil.GetHostname("")
+	}
+
 	if cfgPath != "" {
 		b, err := ioutil.ReadFile(cfgPath)
 		if err != nil {

cmd/kubeadm/app/preflight/checks.go

@@ -599,7 +599,7 @@ func RunJoinNodeChecks(cfg *kubeadmapi.NodeConfiguration) error {
 	checks := []Checker{
 		SystemVerificationCheck{},
 		IsRootCheck{},
-		HostnameCheck{},
+		HostnameCheck{cfg.NodeName},
 		ServiceCheck{Service: "kubelet", CheckIfActive: false},
 		ServiceCheck{Service: "docker", CheckIfActive: true},
 		PortOpenCheck{port: 10250},