Fix incorrect validation on the kubelet

Author: HirazawaUi

pkg/kubelet/kubelet_pods.go

@@ -575,8 +575,8 @@ func (kl *Kubelet) GeneratePodHostNameAndDomain(pod *v1.Pod) (string, string, er
 
 	if utilfeature.DefaultFeatureGate.Enabled(features.HostnameOverride) && pod.Spec.HostnameOverride != nil {
 		hostname := *pod.Spec.HostnameOverride
-		if msgs := utilvalidation.IsDNS1123Label(hostname); len(msgs) != 0 {
-			return "", "", fmt.Errorf("pod HostnameOverride %q is not a valid DNS label: %s", hostname, strings.Join(msgs, ";"))
+		if msgs := utilvalidation.IsDNS1123Subdomain(hostname); len(msgs) != 0 {
+			return "", "", fmt.Errorf("pod HostnameOverride %q is not a valid DNS subdomain: %s", hostname, strings.Join(msgs, ";"))
 		}
 		truncatedHostname, err := truncatePodHostnameIfNeeded(pod.Name, hostname)
 		if err != nil {

pkg/kubelet/kubelet_pods_test.go

@@ -7468,7 +7468,15 @@ func TestGeneratePodHostNameAndDomain(t *testing.T) {
 			podHostnameOverride: ptr.To("Invalid-Hostname-!"),
 			featureGateEnabled:  true,
 			expectError:         true,
-			errorContains:       "pod HostnameOverride \"Invalid-Hostname-!\" is not a valid DNS label",
+			errorContains:       "pod HostnameOverride \"Invalid-Hostname-!\" is not a valid DNS subdomain",
+		},
+		{
+			name:                "HostnameOverride - enabled - overrides all - valid DNS hostname",
+			podName:             "test-pod",
+			podHostnameOverride: ptr.To("valid.hostname"),
+			expectedHostname:    "valid.hostname",
+			featureGateEnabled:  true,
+			errorContains:       "",
 		},
 		{
 			name:                "HostnameOverride - disabled - is ignored",

test/e2e/common/node/pod_hostnameoverride.go

@@ -56,6 +56,14 @@ var _ = SIGDescribe("Override hostname of Pod", framework.WithFeatureGate(featur
 	f := framework.NewDefaultFramework("hostfqdn")
 	f.NamespacePodSecurityLevel = admissionapi.LevelBaseline
 
+	ginkgo.It("a pod has hostnameOverride field with value that is a valid DNS subdomain.", func(ctx context.Context) {
+		pod := newTestPod(f.Namespace.Name)
+		hostnameOverride := "override.example.host"
+		pod.Spec.HostnameOverride = &hostnameOverride
+		output := []string{fmt.Sprintf("%s;%s;", hostnameOverride, hostnameOverride)}
+		e2eoutput.TestContainerOutput(ctx, f, "hostnameOverride overrides hostname", pod, 0, output)
+	})
+
 	ginkgo.It("a pod with hostname and hostnameOverride fields will have hostnameOverride as hostname", func(ctx context.Context) {
 		pod := newTestPod(f.Namespace.Name)
 		hostname := "custom-host"