support null resolvConf in Kubelet Configuration

cmd/kubeadm/app/componentconfigs/kubelet.go

@@ -209,11 +209,11 @@ func (kc *kubeletConfig) Default(cfg *kubeadmapi.ClusterConfiguration, _ *kubead
 		klog.Warningf("cannot determine if systemd-resolved is active: %v", err)
 	}
 	if ok {
-		if kc.config.ResolverConfig == "" {
-			kc.config.ResolverConfig = kubeletSystemdResolverConfig
+		if kc.config.ResolverConfig == nil {
+			kc.config.ResolverConfig = utilpointer.String(kubeletSystemdResolverConfig)
 		} else {
-			if kc.config.ResolverConfig != kubeletSystemdResolverConfig {
-				warnDefaultComponentConfigValue(kind, "resolvConf", kubeletSystemdResolverConfig, kc.config.ResolverConfig)
+			if kc.config.ResolverConfig != utilpointer.String(kubeletSystemdResolverConfig) {
+				warnDefaultComponentConfigValue(kind, "resolvConf", kubeletSystemdResolverConfig, *kc.config.ResolverConfig)
 			}
 		}
 	}

cmd/kubeadm/app/componentconfigs/kubelet_test.go

@@ -50,10 +50,10 @@ func testKubeletConfigMap(contents string) *v1.ConfigMap {
 }
 
 func TestKubeletDefault(t *testing.T) {
-	var resolverConfig string
+	var resolverConfig *string
 	if isSystemdResolvedActive, _ := isServiceActive("systemd-resolved"); isSystemdResolvedActive {
 		// If systemd-resolved is active, we need to set the default resolver config
-		resolverConfig = kubeletSystemdResolverConfig
+		resolverConfig = utilpointer.String(kubeletSystemdResolverConfig)
 	}
 
 	tests := []struct {

pkg/kubelet/apis/config/v1beta1/defaults.go

@@ -181,8 +181,8 @@ func SetDefaults_KubeletConfiguration(obj *kubeletconfigv1beta1.KubeletConfigura
 		temp := int64(-1)
 		obj.PodPidsLimit = &temp
 	}
-	if obj.ResolverConfig == "" {
-		obj.ResolverConfig = kubetypes.ResolvConfDefault
+	if obj.ResolverConfig == nil {
+		obj.ResolverConfig = utilpointer.String(kubetypes.ResolvConfDefault)
 	}
 	if obj.CPUCFSQuota == nil {
 		obj.CPUCFSQuota = utilpointer.BoolPtr(true)

pkg/kubelet/apis/config/v1beta1/zz_generated.conversion.go

@@ -308,7 +308,9 @@ func autoConvert_v1beta1_KubeletConfiguration_To_config_KubeletConfiguration(in
 	if err := v1.Convert_Pointer_int64_To_int64(&in.PodPidsLimit, &out.PodPidsLimit, s); err != nil {
 		return err
 	}
-	out.ResolverConfig = in.ResolverConfig
+	if err := v1.Convert_Pointer_string_To_string(&in.ResolverConfig, &out.ResolverConfig, s); err != nil {
+		return err
+	}
 	out.RunOnce = in.RunOnce
 	if err := v1.Convert_Pointer_bool_To_bool(&in.CPUCFSQuota, &out.CPUCFSQuota, s); err != nil {
 		return err
@@ -479,7 +481,9 @@ func autoConvert_config_KubeletConfiguration_To_v1beta1_KubeletConfiguration(in
 	if err := v1.Convert_int64_To_Pointer_int64(&in.PodPidsLimit, &out.PodPidsLimit, s); err != nil {
 		return err
 	}
-	out.ResolverConfig = in.ResolverConfig
+	if err := v1.Convert_string_To_Pointer_string(&in.ResolverConfig, &out.ResolverConfig, s); err != nil {
+		return err
+	}
 	out.RunOnce = in.RunOnce
 	if err := v1.Convert_bool_To_Pointer_bool(&in.CPUCFSQuota, &out.CPUCFSQuota, s); err != nil {
 		return err

staging/src/k8s.io/kubelet/config/v1beta1/types.go

@@ -599,9 +599,10 @@ type KubeletConfiguration struct {
 	// dynamically updating this field, consider that
 	// changes will only take effect on Pods created after the update. Draining
 	// the node is recommended before changing this field.
+	// If set to the empty string, will override the default and effectively disable DNS lookups.
 	// Default: "/etc/resolv.conf"
 	// +optional
-	ResolverConfig string `json:"resolvConf,omitempty"`
+	ResolverConfig *string `json:"resolvConf,omitempty"`
 	// runOnce causes the Kubelet to check the API server once for pods,
 	// run those in addition to the pods specified by static pod files, and exit.
 	// Default: false

staging/src/k8s.io/kubelet/config/v1beta1/zz_generated.deepcopy.go

@@ -189,6 +189,11 @@ func (in *KubeletConfiguration) DeepCopyInto(out *KubeletConfiguration) {
 		*out = new(int64)
 		**out = **in
 	}
+	if in.ResolverConfig != nil {
+		in, out := &in.ResolverConfig, &out.ResolverConfig
+		*out = new(string)
+		**out = **in
+	}
 	if in.CPUCFSQuota != nil {
 		in, out := &in.CPUCFSQuota, &out.CPUCFSQuota
 		*out = new(bool)