Merge pull request #91980 from rosti/kubeadm-cc-manual-upgrade

kubeadm upgrade: Allow supplying hand migrated component configs

cmd/kubeadm/app/cmd/alpha/certs.go

@@ -254,7 +254,7 @@ func getInternalCfg(cfgPath string, kubeconfigPath string, cfg kubeadmapiv1beta2
 	if cfgPath == "" {
 		client, err := kubeconfigutil.ClientSetFromFile(kubeconfigPath)
 		if err == nil {
-			internalcfg, err := configutil.FetchInitConfigurationFromCluster(client, out, logPrefix, false)
+			internalcfg, err := configutil.FetchInitConfigurationFromCluster(client, out, logPrefix, false, false)
 			if err == nil {
 				fmt.Println() // add empty line to separate the FetchInitConfigurationFromCluster output from the command output
 				return internalcfg, nil

cmd/kubeadm/app/cmd/join.go

@@ -545,7 +545,7 @@ func fetchInitConfiguration(tlsBootstrapCfg *clientcmdapi.Config) (*kubeadmapi.I
 	}
 
 	// Fetches the init configuration
-	initConfiguration, err := configutil.FetchInitConfigurationFromCluster(tlsClient, os.Stdout, "preflight", true)
+	initConfiguration, err := configutil.FetchInitConfigurationFromCluster(tlsClient, os.Stdout, "preflight", true, false)
 	if err != nil {
 		return nil, errors.Wrap(err, "unable to fetch the kubeadm-config ConfigMap")
 	}

cmd/kubeadm/app/cmd/reset.go

@@ -94,7 +94,7 @@ func newResetData(cmd *cobra.Command, options *resetOptions, in io.Reader, out i
 	client, err := getClientset(options.kubeconfigPath, false)
 	if err == nil {
 		klog.V(1).Infof("[reset] Loaded client set from kubeconfig file: %s", options.kubeconfigPath)
-		cfg, err = configutil.FetchInitConfigurationFromCluster(client, out, "reset", false)
+		cfg, err = configutil.FetchInitConfigurationFromCluster(client, out, "reset", false, false)
 		if err != nil {
 			klog.Warningf("[reset] Unable to fetch the kubeadm-config ConfigMap from cluster: %v", err)
 		}

cmd/kubeadm/app/cmd/upgrade/BUILD

@@ -20,6 +20,7 @@ go_library(
         "//cmd/kubeadm/app/cmd/phases/upgrade/node:go_default_library",
         "//cmd/kubeadm/app/cmd/phases/workflow:go_default_library",
         "//cmd/kubeadm/app/cmd/util:go_default_library",
+        "//cmd/kubeadm/app/componentconfigs:go_default_library",
         "//cmd/kubeadm/app/constants:go_default_library",
         "//cmd/kubeadm/app/features:go_default_library",
         "//cmd/kubeadm/app/phases/controlplane:go_default_library",

cmd/kubeadm/app/cmd/upgrade/apply.go

@@ -73,12 +73,7 @@ func NewCmdApply(apf *applyPlanFlags) *cobra.Command {
 		DisableFlagsInUseLine: true,
 		Short:                 "Upgrade your Kubernetes cluster to the specified version",
 		RunE: func(cmd *cobra.Command, args []string) error {
-			userVersion, err := getK8sVersionFromUserInput(flags.applyPlanFlags, args, true)
-			if err != nil {
-				return err
-			}
-
-			return runApply(flags, userVersion)
+			return runApply(flags, args)
 		},
 	}
 
@@ -110,12 +105,12 @@ func NewCmdApply(apf *applyPlanFlags) *cobra.Command {
 //   - Creating the RBAC rules for the bootstrap tokens and the cluster-info ConfigMap
 //   - Applying new kube-dns and kube-proxy manifests
 //   - Uploads the newly used configuration to the cluster ConfigMap
-func runApply(flags *applyFlags, userVersion string) error {
+func runApply(flags *applyFlags, args []string) error {
 
 	// Start with the basics, verify that the cluster is healthy and get the configuration from the cluster (using the ConfigMap)
 	klog.V(1).Infoln("[upgrade/apply] verifying health of cluster")
 	klog.V(1).Infoln("[upgrade/apply] retrieving configuration from cluster")
-	client, versionGetter, cfg, err := enforceRequirements(flags.applyPlanFlags, flags.dryRun, userVersion)
+	client, versionGetter, cfg, err := enforceRequirements(flags.applyPlanFlags, args, flags.dryRun, true)
 	if err != nil {
 		return err
 	}

cmd/kubeadm/app/cmd/upgrade/common.go

@@ -21,6 +21,7 @@ import (
 	"bytes"
 	"fmt"
 	"io"
+	"io/ioutil"
 	"os"
 	"strings"
 	"time"
@@ -36,47 +37,91 @@ import (
 	kubeadmapi "k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm"
 	"k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm/validation"
 	cmdutil "k8s.io/kubernetes/cmd/kubeadm/app/cmd/util"
+	"k8s.io/kubernetes/cmd/kubeadm/app/componentconfigs"
 	"k8s.io/kubernetes/cmd/kubeadm/app/constants"
 	"k8s.io/kubernetes/cmd/kubeadm/app/features"
 	"k8s.io/kubernetes/cmd/kubeadm/app/phases/upgrade"
 	"k8s.io/kubernetes/cmd/kubeadm/app/preflight"
+	kubeadmutil "k8s.io/kubernetes/cmd/kubeadm/app/util"
 	"k8s.io/kubernetes/cmd/kubeadm/app/util/apiclient"
 	configutil "k8s.io/kubernetes/cmd/kubeadm/app/util/config"
 	dryrunutil "k8s.io/kubernetes/cmd/kubeadm/app/util/dryrun"
 	kubeconfigutil "k8s.io/kubernetes/cmd/kubeadm/app/util/kubeconfig"
 )
 
-func getK8sVersionFromUserInput(flags *applyPlanFlags, args []string, versionIsMandatory bool) (string, error) {
-	var userVersion string
+// isKubeadmConfigPresent checks if a kubeadm config type is found in the provided document map
+func isKubeadmConfigPresent(docmap kubeadmapi.DocumentMap) bool {
+	for gvk := range docmap {
+		if gvk.Group == kubeadmapi.GroupName {
+			return true
+		}
+	}
+	return false
+}
 
-	// If the version is specified in config file, pick up that value.
-	if flags.cfgPath != "" {
-		// Note that cfg isn't preserved here, it's just an one-off to populate userVersion based on --config
-		cfg, err := configutil.LoadInitConfigurationFromFile(flags.cfgPath)
+// loadConfig loads configuration from a file and/or the cluster. InitConfiguration, ClusterConfiguration and (optionally) component configs
+// are loaded. This function allows the component configs to be loaded from a file that contains only them. If the file contains any kubeadm types
+// in it (API group "kubeadm.kubernetes.io" present), then the supplied file is treaded as a legacy reconfiguration style "--config" use and the
+// returned bool value is set to true (the only case to be done so).
+func loadConfig(cfgPath string, client clientset.Interface, skipComponentConfigs bool) (*kubeadmapi.InitConfiguration, bool, error) {
+	// Used for info logs here
+	const logPrefix = "upgrade/config"
+
+	// The usual case here is to not have a config file, but rather load the config from the cluster.
+	// This is probably 90% of the time. So we handle it first.
+	if cfgPath == "" {
+		cfg, err := configutil.FetchInitConfigurationFromCluster(client, os.Stdout, logPrefix, false, skipComponentConfigs)
+		return cfg, false, err
+	}
+
+	// Otherwise, we have a config file. Let's load it.
+	configBytes, err := ioutil.ReadFile(cfgPath)
 	if err != nil {
-			return "", err
+		return nil, false, errors.Wrapf(err, "unable to load config from file %q", cfgPath)
 	}
 
-		userVersion = cfg.KubernetesVersion
+	// Split the YAML documents in the file into a DocumentMap
+	docmap, err := kubeadmutil.SplitYAMLDocuments(configBytes)
+	if err != nil {
+		return nil, false, err
 	}
 
-	// the version arg is mandatory unless version is specified in the config file
-	if versionIsMandatory && userVersion == "" {
-		if err := cmdutil.ValidateExactArgNumber(args, []string{"version"}); err != nil {
-			return "", err
+	// If there are kubeadm types (API group kubeadm.kubernetes.io) present, we need to keep the existing behavior
+	// here. Basically, we have to load all of the configs from the file and none from the cluster. Configs that are
+	// missing from the file will be automatically regenerated by kubeadm even if they are present in the cluster.
+	// The resulting configs overwrite the existing cluster ones at the end of a successful upgrade apply operation.
+	if isKubeadmConfigPresent(docmap) {
+		klog.Warning("WARNING: Usage of the --config flag with kubeadm config types for reconfiguring the cluster during upgrade is not recommended!")
+		cfg, err := configutil.BytesToInitConfiguration(configBytes)
+		return cfg, true, err
+	}
+
+	// If no kubeadm config types are present, we assume that there are manually upgraded component configs in the file.
+	// Hence, we load the kubeadm types from the cluster.
+	initCfg, err := configutil.FetchInitConfigurationFromCluster(client, os.Stdout, logPrefix, false, true)
+	if err != nil {
+		return nil, false, err
+	}
+
+	// Stop here if the caller does not want us to load the component configs
+	if !skipComponentConfigs {
+		// Load the component configs with upgrades
+		if err := componentconfigs.FetchFromClusterWithLocalOverwrites(&initCfg.ClusterConfiguration, client, docmap); err != nil {
+			return nil, false, err
+		}
+
+		// Now default and validate the configs
+		componentconfigs.Default(&initCfg.ClusterConfiguration, &initCfg.LocalAPIEndpoint, &initCfg.NodeRegistration)
+		if errs := componentconfigs.Validate(&initCfg.ClusterConfiguration); len(errs) != 0 {
+			return nil, false, errs.ToAggregate()
 		}
 	}
 
-	// If option was specified in both args and config file, args will overwrite the config file.
-	if len(args) == 1 {
-		userVersion = args[0]
-	}
-
-	return userVersion, nil
+	return initCfg, false, nil
 }
 
 // enforceRequirements verifies that it's okay to upgrade and then returns the variables needed for the rest of the procedure
-func enforceRequirements(flags *applyPlanFlags, dryRun bool, newK8sVersion string) (clientset.Interface, upgrade.VersionGetter, *kubeadmapi.InitConfiguration, error) {
+func enforceRequirements(flags *applyPlanFlags, args []string, dryRun bool, upgradeApply bool) (clientset.Interface, upgrade.VersionGetter, *kubeadmapi.InitConfiguration, error) {
 	client, err := getClient(flags.kubeConfigPath, dryRun)
 	if err != nil {
 		return nil, nil, nil, errors.Wrapf(err, "couldn't create a Kubernetes client from file %q", flags.kubeConfigPath)
@@ -90,14 +135,8 @@ func enforceRequirements(flags *applyPlanFlags, dryRun bool, newK8sVersion strin
 	// Fetch the configuration from a file or ConfigMap and validate it
 	fmt.Println("[upgrade/config] Making sure the configuration is correct:")
 
-	var cfg *kubeadmapi.InitConfiguration
-	if flags.cfgPath != "" {
-		klog.Warning("WARNING: Usage of the --config flag for reconfiguring the cluster during upgrade is not recommended!")
-		cfg, err = configutil.LoadInitConfigurationFromFile(flags.cfgPath)
-	} else {
-		cfg, err = configutil.FetchInitConfigurationFromCluster(client, os.Stdout, "upgrade/config", false)
-	}
-
+	var newK8sVersion string
+	cfg, legacyReconfigure, err := loadConfig(flags.cfgPath, client, !upgradeApply)
 	if err != nil {
 		if apierrors.IsNotFound(err) {
 			fmt.Printf("[upgrade/config] In order to upgrade, a ConfigMap called %q in the %s namespace must exist.\n", constants.KubeadmConfigConfigMap, metav1.NamespaceSystem)
@@ -111,6 +150,11 @@ func enforceRequirements(flags *applyPlanFlags, dryRun bool, newK8sVersion strin
 			err = errors.Errorf("the ConfigMap %q in the %s namespace used for getting configuration information was not found", constants.KubeadmConfigConfigMap, metav1.NamespaceSystem)
 		}
 		return nil, nil, nil, errors.Wrap(err, "[upgrade/config] FATAL")
+	} else if legacyReconfigure {
+		// Set the newK8sVersion to the value in the ClusterConfiguration. This is done, so that users who use the --config option
+		// to supply a new ClusterConfiguration don't have to specify the Kubernetes version twice,
+		// if they don't want to upgrade but just change a setting.
+		newK8sVersion = cfg.KubernetesVersion
 	}
 
 	ignorePreflightErrorsSet, err := validation.ValidateIgnorePreflightErrors(flags.ignorePreflightErrors, cfg.NodeRegistration.IgnorePreflightErrors)
@@ -131,8 +175,16 @@ func enforceRequirements(flags *applyPlanFlags, dryRun bool, newK8sVersion strin
 		return nil, nil, nil, errors.Wrap(err, "[upgrade/health] FATAL")
 	}
 
-	// If a new k8s version should be set, apply the change before printing the config
-	if len(newK8sVersion) != 0 {
+	// The version arg is mandatory, during upgrade apply, unless it's specified in the config file
+	if upgradeApply && newK8sVersion == "" {
+		if err := cmdutil.ValidateExactArgNumber(args, []string{"version"}); err != nil {
+			return nil, nil, nil, err
+		}
+	}
+
+	// If option was specified in both args and config file, args will overwrite the config file.
+	if len(args) == 1 {
+		newK8sVersion = args[0]
 		cfg.KubernetesVersion = newK8sVersion
 	}
 

cmd/kubeadm/app/cmd/upgrade/common_test.go

@@ -18,98 +18,11 @@ package upgrade
 
 import (
 	"bytes"
-	"io/ioutil"
-	"os"
 	"testing"
 
 	kubeadmapi "k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm"
-	"k8s.io/kubernetes/cmd/kubeadm/app/constants"
 )
 
-func TestGetK8sVersionFromUserInput(t *testing.T) {
-	currentVersion := "v" + constants.CurrentKubernetesVersion.String()
-	validConfig := "apiVersion: kubeadm.k8s.io/v1beta2\n" +
-		"kind: ClusterConfiguration\n" +
-		"kubernetesVersion: " + currentVersion
-
-	var tcases = []struct {
-		name               string
-		isVersionMandatory bool
-		clusterConfig      string
-		args               []string
-		expectedErr        bool
-		expectedVersion    string
-	}{
-		{
-			name:               "No config and version as an argument",
-			isVersionMandatory: true,
-			args:               []string{"v1.13.1"},
-			expectedVersion:    "v1.13.1",
-		},
-		{
-			name:               "Neither config nor version specified",
-			isVersionMandatory: true,
-			expectedErr:        true,
-		},
-		{
-			name:               "No config and empty version as an argument",
-			isVersionMandatory: true,
-			args:               []string{""},
-			expectedErr:        true,
-		},
-		{
-			name:               "Valid config, but no version specified",
-			isVersionMandatory: true,
-			clusterConfig:      validConfig,
-			expectedVersion:    currentVersion,
-		},
-		{
-			name:               "Valid config and different version specified",
-			isVersionMandatory: true,
-			clusterConfig:      validConfig,
-			args:               []string{"v1.13.1"},
-			expectedVersion:    "v1.13.1",
-		},
-		{
-			name: "Version is optional",
-		},
-	}
-	for _, tt := range tcases {
-		t.Run(tt.name, func(t *testing.T) {
-			flags := &applyPlanFlags{}
-			if len(tt.clusterConfig) > 0 {
-				file, err := ioutil.TempFile("", "kubeadm-upgrade-common-test-*.yaml")
-				if err != nil {
-					t.Fatalf("Failed to create test config file: %+v", err)
-				}
-
-				tmpFileName := file.Name()
-				defer os.Remove(tmpFileName)
-
-				_, err = file.WriteString(tt.clusterConfig)
-				file.Close()
-				if err != nil {
-					t.Fatalf("Failed to write test config file contents: %+v", err)
-				}
-
-				flags.cfgPath = tmpFileName
-			}
-
-			userVersion, err := getK8sVersionFromUserInput(flags, tt.args, tt.isVersionMandatory)
-
-			if err == nil && tt.expectedErr {
-				t.Error("Expected error, but got success")
-			}
-			if err != nil && !tt.expectedErr {
-				t.Errorf("Unexpected error: %+v", err)
-			}
-			if userVersion != tt.expectedVersion {
-				t.Errorf("Expected %q, but got %q", tt.expectedVersion, userVersion)
-			}
-		})
-	}
-}
-
 func TestEnforceRequirements(t *testing.T) {
 	tcases := []struct {
 		name          string
@@ -139,7 +52,7 @@ func TestEnforceRequirements(t *testing.T) {
 	}
 	for _, tt := range tcases {
 		t.Run(tt.name, func(t *testing.T) {
-			_, _, _, err := enforceRequirements(&tt.flags, tt.dryRun, tt.newK8sVersion)
+			_, _, _, err := enforceRequirements(&tt.flags, nil, tt.dryRun, false)
 
 			if err == nil && tt.expectedErr {
 				t.Error("Expected error, but got success")

cmd/kubeadm/app/cmd/upgrade/diff.go

@@ -91,7 +91,7 @@ func runDiff(flags *diffFlags, args []string) error {
 		if err != nil {
 			return errors.Wrapf(err, "couldn't create a Kubernetes client from file %q", flags.kubeConfigPath)
 		}
-		cfg, err = configutil.FetchInitConfigurationFromCluster(client, flags.out, "upgrade/diff", false)
+		cfg, err = configutil.FetchInitConfigurationFromCluster(client, flags.out, "upgrade/diff", false, false)
 	}
 	if err != nil {
 		return err

cmd/kubeadm/app/cmd/upgrade/node.go

@@ -141,7 +141,7 @@ func newNodeData(cmd *cobra.Command, args []string, options *nodeOptions) (*node
 	// Fetches the cluster configuration
 	// NB in case of control-plane node, we are reading all the info for the node; in case of NOT control-plane node
 	//    (worker node), we are not reading local API address and the CRI socket from the node object
-	cfg, err := configutil.FetchInitConfigurationFromCluster(client, os.Stdout, "upgrade", !isControlPlaneNode)
+	cfg, err := configutil.FetchInitConfigurationFromCluster(client, os.Stdout, "upgrade", !isControlPlaneNode, false)
 	if err != nil {
 		return nil, errors.Wrap(err, "unable to fetch the kubeadm-config ConfigMap")
 	}

cmd/kubeadm/app/cmd/upgrade/plan.go

@@ -48,12 +48,7 @@ func NewCmdPlan(apf *applyPlanFlags) *cobra.Command {
 		Use:   "plan [version] [flags]",
 		Short: "Check which versions are available to upgrade to and validate whether your current cluster is upgradeable. To skip the internet check, pass in the optional [version] parameter",
 		RunE: func(_ *cobra.Command, args []string) error {
-			userVersion, err := getK8sVersionFromUserInput(flags.applyPlanFlags, args, false)
-			if err != nil {
-				return err
-			}
-
-			return runPlan(flags, userVersion)
+			return runPlan(flags, args)
 		},
 	}
 
@@ -63,11 +58,11 @@ func NewCmdPlan(apf *applyPlanFlags) *cobra.Command {
 }
 
 // runPlan takes care of outputting available versions to upgrade to for the user
-func runPlan(flags *planFlags, userVersion string) error {
+func runPlan(flags *planFlags, args []string) error {
 	// Start with the basics, verify that the cluster is healthy, build a client and a versionGetter. Never dry-run when planning.
 	klog.V(1).Infoln("[upgrade/plan] verifying health of cluster")
 	klog.V(1).Infoln("[upgrade/plan] retrieving configuration from cluster")
-	client, versionGetter, cfg, err := enforceRequirements(flags.applyPlanFlags, false, userVersion)
+	client, versionGetter, cfg, err := enforceRequirements(flags.applyPlanFlags, args, false, false)
 	if err != nil {
 		return err
 	}

cmd/kubeadm/app/componentconfigs/configset.go

@@ -239,6 +239,49 @@ func FetchFromDocumentMap(clusterCfg *kubeadmapi.ClusterConfiguration, docmap ku
 	return nil
 }
 
+// FetchFromClusterWithLocalOverwrites fetches component configs from a cluster and overwrites them locally with
+// the ones present in the supplied document map. If any UnsupportedConfigVersionError are not handled by the configs
+// in the document map, the function returns them all as a single UnsupportedConfigVersionsErrorMap.
+// This function is normally called only in some specific cases during upgrade.
+func FetchFromClusterWithLocalOverwrites(clusterCfg *kubeadmapi.ClusterConfiguration, client clientset.Interface, docmap kubeadmapi.DocumentMap) error {
+	ensureInitializedComponentConfigs(clusterCfg)
+
+	oldVersionErrs := UnsupportedConfigVersionsErrorMap{}
+
+	for _, handler := range known {
+		componentCfg, err := handler.FromCluster(client, clusterCfg)
+		if err != nil {
+			if vererr, ok := err.(*UnsupportedConfigVersionError); ok {
+				oldVersionErrs[handler.GroupVersion.Group] = vererr
+			} else {
+				return err
+			}
+		} else if componentCfg != nil {
+			clusterCfg.ComponentConfigs[handler.GroupVersion.Group] = componentCfg
+		}
+	}
+
+	for _, handler := range known {
+		componentCfg, err := handler.FromDocumentMap(docmap)
+		if err != nil {
+			if vererr, ok := err.(*UnsupportedConfigVersionError); ok {
+				oldVersionErrs[handler.GroupVersion.Group] = vererr
+			} else {
+				return err
+			}
+		} else if componentCfg != nil {
+			clusterCfg.ComponentConfigs[handler.GroupVersion.Group] = componentCfg
+			delete(oldVersionErrs, handler.GroupVersion.Group)
+		}
+	}
+
+	if len(oldVersionErrs) != 0 {
+		return oldVersionErrs
+	}
+
+	return nil
+}
+
 // Validate is a placeholder for performing a validation on an already loaded component configs in a ClusterConfiguration
 // Currently it prints a warning that no validation was performed
 func Validate(clusterCfg *kubeadmapi.ClusterConfiguration) field.ErrorList {

cmd/kubeadm/app/componentconfigs/configset_test.go

@@ -110,3 +110,139 @@ func TestFetchFromDocumentMap(t *testing.T) {
 		t.Fatalf("missmatch between supplied and loaded type numbers:\n\tgot: %d\n\texpected: %d", len(clusterCfg.ComponentConfigs), len(gvkmap))
 	}
 }
+
+func kubeproxyConfigMap(contents string) *v1.ConfigMap {
+	return &v1.ConfigMap{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:      constants.KubeProxyConfigMap,
+			Namespace: metav1.NamespaceSystem,
+		},
+		Data: map[string]string{
+			constants.KubeProxyConfigMapKey: dedent.Dedent(contents),
+		},
+	}
+}
+
+func TestFetchFromClusterWithLocalUpgrades(t *testing.T) {
+	cases := []struct {
+		desc          string
+		obj           runtime.Object
+		config        string
+		expectedValue string
+		expectedErr   bool
+	}{
+		{
+			desc: "reconginzed cluster object without overwrite is used",
+			obj: kubeproxyConfigMap(`
+				apiVersion: kubeproxy.config.k8s.io/v1alpha1
+				kind: KubeProxyConfiguration
+				hostnameOverride: foo
+			`),
+			expectedValue: "foo",
+		},
+		{
+			desc: "reconginzed cluster object with overwrite is not used",
+			obj: kubeproxyConfigMap(`
+				apiVersion: kubeproxy.config.k8s.io/v1alpha1
+				kind: KubeProxyConfiguration
+				hostnameOverride: foo
+			`),
+			config: dedent.Dedent(`
+				apiVersion: kubeproxy.config.k8s.io/v1alpha1
+				kind: KubeProxyConfiguration
+				hostnameOverride: bar
+			`),
+			expectedValue: "bar",
+		},
+		{
+			desc: "old config without overwrite returns an error",
+			obj: kubeproxyConfigMap(`
+				apiVersion: kubeproxy.config.k8s.io/v1alpha0
+				kind: KubeProxyConfiguration
+				hostnameOverride: foo
+			`),
+			expectedErr: true,
+		},
+		{
+			desc: "old config with recognized overwrite returns success",
+			obj: kubeproxyConfigMap(`
+				apiVersion: kubeproxy.config.k8s.io/v1alpha0
+				kind: KubeProxyConfiguration
+				hostnameOverride: foo
+			`),
+			config: dedent.Dedent(`
+				apiVersion: kubeproxy.config.k8s.io/v1alpha1
+				kind: KubeProxyConfiguration
+				hostnameOverride: bar
+			`),
+			expectedValue: "bar",
+		},
+		{
+			desc: "old config with old overwrite returns an error",
+			obj: kubeproxyConfigMap(`
+				apiVersion: kubeproxy.config.k8s.io/v1alpha0
+				kind: KubeProxyConfiguration
+				hostnameOverride: foo
+			`),
+			config: dedent.Dedent(`
+				apiVersion: kubeproxy.config.k8s.io/v1alpha0
+				kind: KubeProxyConfiguration
+				hostnameOverride: bar
+			`),
+			expectedErr: true,
+		},
+	}
+	for _, test := range cases {
+		t.Run(test.desc, func(t *testing.T) {
+			clusterCfg := &kubeadmapi.ClusterConfiguration{
+				KubernetesVersion: constants.CurrentKubernetesVersion.String(),
+			}
+
+			k8sVersion := version.MustParseGeneric(clusterCfg.KubernetesVersion)
+
+			client := clientsetfake.NewSimpleClientset(
+				test.obj,
+				&v1.ConfigMap{
+					ObjectMeta: metav1.ObjectMeta{
+						Name:      constants.GetKubeletConfigMapName(k8sVersion),
+						Namespace: metav1.NamespaceSystem,
+					},
+					Data: map[string]string{
+						constants.KubeletBaseConfigurationConfigMapKey: dedent.Dedent(`
+							apiVersion: kubelet.config.k8s.io/v1beta1
+							kind: KubeletConfiguration
+						`),
+					},
+				},
+			)
+
+			docmap, err := kubeadmutil.SplitYAMLDocuments([]byte(test.config))
+			if err != nil {
+				t.Fatalf("unexpected failure of SplitYAMLDocuments: %v", err)
+			}
+
+			err = FetchFromClusterWithLocalOverwrites(clusterCfg, client, docmap)
+			if err != nil {
+				if !test.expectedErr {
+					t.Errorf("unexpected failure: %v", err)
+				}
+			} else {
+				if test.expectedErr {
+					t.Error("unexpected success")
+				} else {
+					kubeproxyCfg, ok := clusterCfg.ComponentConfigs[KubeProxyGroup]
+					if !ok {
+						t.Error("the config was reported as loaded, but was not in reality")
+					} else {
+						actualConfig, ok := kubeproxyCfg.(*kubeProxyConfig)
+						if !ok {
+							t.Error("the config is not of the expected type")
+						} else if actualConfig.config.HostnameOverride != test.expectedValue {
+							t.Errorf("unexpected value:\n\tgot: %q\n\texpected: %q", actualConfig.config.HostnameOverride, test.expectedValue)
+						}
+					}
+				}
+			}
+		})
+	}
+}

cmd/kubeadm/app/componentconfigs/utils.go

@@ -18,6 +18,8 @@ package componentconfigs
 
 import (
 	"fmt"
+	"sort"
+	"strings"
 
 	"k8s.io/apimachinery/pkg/runtime/schema"
 	"k8s.io/klog/v2"
@@ -40,6 +42,27 @@ func (err *UnsupportedConfigVersionError) Error() string {
 	return fmt.Sprintf("unsupported apiVersion %q, you may have to do manual conversion to %q and run kubeadm again", err.OldVersion, err.CurrentVersion)
 }
 
+// UnsupportedConfigVersionsErrorMap is a cumulative version of the UnsupportedConfigVersionError type
+type UnsupportedConfigVersionsErrorMap map[string]*UnsupportedConfigVersionError
+
+// Error implements the standard Golang error interface for UnsupportedConfigVersionsErrorMap
+func (errs UnsupportedConfigVersionsErrorMap) Error() string {
+	// Make sure the error messages we print are predictable by sorting them by the group names involved
+	groups := make([]string, 0, len(errs))
+	for group := range errs {
+		groups = append(groups, group)
+	}
+	sort.Strings(groups)
+
+	msgs := make([]string, 1, 1+len(errs))
+	msgs[0] = "multiple unsupported config version errors encountered:"
+	for _, group := range groups {
+		msgs = append(msgs, errs[group].Error())
+	}
+
+	return strings.Join(msgs, "\n\t- ")
+}
+
 // warnDefaultComponentConfigValue prints a warning if the user modified a field in a certain
 // CompomentConfig from the default recommended value in kubeadm.
 func warnDefaultComponentConfigValue(componentConfigKind, paramName string, defaultValue, userValue interface{}) {

cmd/kubeadm/app/util/config/cluster.go

@@ -61,12 +61,12 @@ func (ue *unretriableError) Error() string {
 }
 
 // FetchInitConfigurationFromCluster fetches configuration from a ConfigMap in the cluster
-func FetchInitConfigurationFromCluster(client clientset.Interface, w io.Writer, logPrefix string, newControlPlane bool) (*kubeadmapi.InitConfiguration, error) {
+func FetchInitConfigurationFromCluster(client clientset.Interface, w io.Writer, logPrefix string, newControlPlane, skipComponentConfigs bool) (*kubeadmapi.InitConfiguration, error) {
 	fmt.Fprintf(w, "[%s] Reading configuration from the cluster...\n", logPrefix)
 	fmt.Fprintf(w, "[%s] FYI: You can look at this config file with 'kubectl -n %s get cm %s -oyaml'\n", logPrefix, metav1.NamespaceSystem, constants.KubeadmConfigConfigMap)
 
 	// Fetch the actual config from cluster
-	cfg, err := getInitConfigurationFromCluster(constants.KubernetesDir, client, newControlPlane)
+	cfg, err := getInitConfigurationFromCluster(constants.KubernetesDir, client, newControlPlane, skipComponentConfigs)
 	if err != nil {
 		return nil, err
 	}
@@ -80,7 +80,7 @@ func FetchInitConfigurationFromCluster(client clientset.Interface, w io.Writer,
 }
 
 // getInitConfigurationFromCluster is separate only for testing purposes, don't call it directly, use FetchInitConfigurationFromCluster instead
-func getInitConfigurationFromCluster(kubeconfigDir string, client clientset.Interface, newControlPlane bool) (*kubeadmapi.InitConfiguration, error) {
+func getInitConfigurationFromCluster(kubeconfigDir string, client clientset.Interface, newControlPlane, skipComponentConfigs bool) (*kubeadmapi.InitConfiguration, error) {
 	// Also, the config map really should be KubeadmConfigConfigMap...
 	configMap, err := apiclient.GetConfigMapWithRetry(client, metav1.NamespaceSystem, constants.KubeadmConfigConfigMap)
 	if err != nil {
@@ -99,10 +99,12 @@ func getInitConfigurationFromCluster(kubeconfigDir string, client clientset.Inte
 		return nil, errors.Wrap(err, "failed to decode cluster configuration data")
 	}
 
-	// gets the component configs from the corresponding config maps
+	if !skipComponentConfigs {
+		// get the component configs from the corresponding config maps
 		if err := componentconfigs.FetchFromCluster(&initcfg.ClusterConfiguration, client); err != nil {
 			return nil, errors.Wrap(err, "failed to get component configs")
 		}
+	}
 
 	// if this isn't a new controlplane instance (e.g. in case of kubeadm upgrades)
 	// get nodes specific information as well

cmd/kubeadm/app/util/config/cluster_test.go

@@ -736,7 +736,7 @@ func TestGetInitConfigurationFromCluster(t *testing.T) {
 				}
 			}
 
-			cfg, err := getInitConfigurationFromCluster(tmpdir, client, rt.newControlPlane)
+			cfg, err := getInitConfigurationFromCluster(tmpdir, client, rt.newControlPlane, false)
 			if rt.expectedError != (err != nil) {
 				t.Errorf("unexpected return err from getInitConfigurationFromCluster: %v", err)
 				return