Merge pull request #130354 from siyuanfoundation/forward-api

KEP-4330: add forward compatibility for compatibility mode

cmd/kube-apiserver/app/options/options_test.go

@@ -128,6 +128,8 @@ func TestAddFlags(t *testing.T) {
 		"--service-cluster-ip-range=192.168.128.0/17",
 		"--lease-reuse-duration-seconds=100",
 		"--emulated-version=test=1.31",
+		"--emulation-forward-compatible=true",
+		"--runtime-config-emulation-forward-compatible=true",
 	}
 	fs.Parse(args)
 	utilruntime.Must(componentGlobalsRegistry.Set())
@@ -136,17 +138,19 @@ func TestAddFlags(t *testing.T) {
 	expected := &ServerRunOptions{
 		Options: &controlplaneapiserver.Options{
 			GenericServerRunOptions: &apiserveroptions.ServerRunOptions{
-				AdvertiseAddress:             netutils.ParseIPSloppy("192.168.10.10"),
+				AdvertiseAddress:                        netutils.ParseIPSloppy("192.168.10.10"),
-				CorsAllowedOriginList:        []string{"10.10.10.100", "10.10.10.200"},
+				CorsAllowedOriginList:                   []string{"10.10.10.100", "10.10.10.200"},
-				MaxRequestsInFlight:          400,
+				MaxRequestsInFlight:                     400,
-				MaxMutatingRequestsInFlight:  200,
+				MaxMutatingRequestsInFlight:             200,
-				RequestTimeout:               time.Duration(2) * time.Minute,
+				RequestTimeout:                          time.Duration(2) * time.Minute,
-				MinRequestTimeout:            1800,
+				MinRequestTimeout:                       1800,
-				StorageInitializationTimeout: time.Minute,
+				StorageInitializationTimeout:            time.Minute,
-				JSONPatchMaxCopyBytes:        int64(3 * 1024 * 1024),
+				JSONPatchMaxCopyBytes:                   int64(3 * 1024 * 1024),
-				MaxRequestBodyBytes:          int64(3 * 1024 * 1024),
+				MaxRequestBodyBytes:                     int64(3 * 1024 * 1024),
-				ComponentGlobalsRegistry:     componentGlobalsRegistry,
+				ComponentGlobalsRegistry:                componentGlobalsRegistry,
-				ComponentName:                basecompatibility.DefaultKubeComponent,
+				ComponentName:                           basecompatibility.DefaultKubeComponent,
+				EmulationForwardCompatible:              true,
+				RuntimeConfigEmulationForwardCompatible: true,
 			},
 			Admission: &kubeoptions.AdmissionOptions{
 				GenericAdmission: &apiserveroptions.AdmissionOptions{

pkg/controlplane/apiserver/apis.go

@@ -89,7 +89,12 @@ func (s *Server) InstallAPIs(restStorageProviders ...RESTStorageProvider) error
 	nonLegacy := []*genericapiserver.APIGroupInfo{}
 
 	// used later in the loop to filter the served resource by those that have expired.
-	resourceExpirationEvaluator, err := genericapiserver.NewResourceExpirationEvaluator(s.GenericAPIServer.EffectiveVersion.EmulationVersion())
+	resourceExpirationEvaluatorOpts := genericapiserver.ResourceExpirationEvaluatorOptions{
+		CurrentVersion:                          s.GenericAPIServer.EffectiveVersion.EmulationVersion(),
+		EmulationForwardCompatible:              s.GenericAPIServer.EmulationForwardCompatible,
+		RuntimeConfigEmulationForwardCompatible: s.GenericAPIServer.RuntimeConfigEmulationForwardCompatible,
+	}
+	resourceExpirationEvaluator, err := genericapiserver.NewResourceExpirationEvaluatorFromOptions(resourceExpirationEvaluatorOpts)
 	if err != nil {
 		return err
 	}
@@ -107,10 +112,13 @@ func (s *Server) InstallAPIs(restStorageProviders ...RESTStorageProvider) error
 			continue
 		}
 
-		// Remove resources that serving kinds that are removed.
+		// Remove resources that serving kinds that are removed or not introduced yet at the current version.
 		// We do this here so that we don't accidentally serve versions without resources or openapi information that for kinds we don't serve.
 		// This is a spot above the construction of individual storage handlers so that no sig accidentally forgets to check.
-		resourceExpirationEvaluator.RemoveDeletedKinds(groupName, apiGroupInfo.Scheme, apiGroupInfo.VersionedResourcesStorageMap)
+		err = resourceExpirationEvaluator.RemoveUnavailableKinds(groupName, apiGroupInfo.Scheme, apiGroupInfo.VersionedResourcesStorageMap, s.APIResourceConfigSource)
+		if err != nil {
+			return err
+		}
 		if len(apiGroupInfo.VersionedResourcesStorageMap) == 0 {
 			klog.V(1).Infof("Removing API group %v because it is time to stop serving it because it has no versions per APILifecycle.", groupName)
 			continue

staging/src/k8s.io/apimachinery/pkg/runtime/interfaces.go

@@ -259,6 +259,7 @@ type ObjectDefaulter interface {
 
 type ObjectVersioner interface {
 	ConvertToVersion(in Object, gv GroupVersioner) (out Object, err error)
+	PrioritizedVersionsForGroup(group string) []schema.GroupVersion
 }
 
 // ObjectConvertor converts an object to a different version.

staging/src/k8s.io/apiserver/pkg/server/config.go

@@ -154,6 +154,15 @@ type Config struct {
 	// EffectiveVersion determines which apis and features are available
 	// based on when the api/feature lifecyle.
 	EffectiveVersion basecompatibility.EffectiveVersion
+	// EmulationForwardCompatible is an option to implicitly enable all APIs which are introduced after the emulation version and
+	// have higher priority than APIs of the same group resource enabled at the emulation version.
+	// If true, all APIs that have higher priority than the APIs of the same group resource enabled at the emulation version will be installed.
+	// This is needed when a controller implementation migrates to newer API versions, for the binary version, and also uses the newer API versions even when emulation version is set.
+	EmulationForwardCompatible bool
+	// RuntimeConfigEmulationForwardCompatible is an option to explicitly enable specific APIs introduced after the emulation version through the runtime-config.
+	// If true, APIs identified by group/version that are enabled in the --runtime-config flag will be installed even if it is introduced after the emulation version. --runtime-config flag values that identify multiple APIs, such as api/all,api/ga,api/beta, are not influenced by this flag and will only enable APIs available at the current emulation version.
+	// If false, error would be thrown if any GroupVersion or GroupVersionResource explicitly enabled in the --runtime-config flag is introduced after the emulation version.
+	RuntimeConfigEmulationForwardCompatible bool
 	// FeatureGate is a way to plumb feature gate through if you have them.
 	FeatureGate featuregate.FeatureGate
 	// AuditBackend is where audit events are sent to.
@@ -839,8 +848,10 @@ func (c completedConfig) New(name string, delegationTarget DelegationTarget) (*G
 		StorageReadinessHook:  NewStorageReadinessHook(c.StorageInitializationTimeout),
 		StorageVersionManager: c.StorageVersionManager,
 
-		EffectiveVersion: c.EffectiveVersion,
+		EffectiveVersion:                        c.EffectiveVersion,
-		FeatureGate:      c.FeatureGate,
+		EmulationForwardCompatible:              c.EmulationForwardCompatible,
+		RuntimeConfigEmulationForwardCompatible: c.RuntimeConfigEmulationForwardCompatible,
+		FeatureGate:                             c.FeatureGate,
 
 		muxAndDiscoveryCompleteSignals: map[string]<-chan struct{}{},
 	}

staging/src/k8s.io/apiserver/pkg/server/deleted_kinds.go

@@ -19,6 +19,7 @@ package server
 import (
 	"fmt"
 	"os"
+	"regexp"
 	"strconv"
 	"strings"
 
@@ -28,13 +29,18 @@ import (
 	"k8s.io/apimachinery/pkg/util/sets"
 	apimachineryversion "k8s.io/apimachinery/pkg/util/version"
 	"k8s.io/apiserver/pkg/registry/rest"
+	serverstorage "k8s.io/apiserver/pkg/server/storage"
 	"k8s.io/klog/v2"
 )
 
+var alphaPattern = regexp.MustCompile(`^v\d+alpha\d+$`)
+
 // resourceExpirationEvaluator holds info for deciding if a particular rest.Storage needs to excluded from the API
 type resourceExpirationEvaluator struct {
-	currentVersion *apimachineryversion.Version
+	currentVersion                          *apimachineryversion.Version
-	isAlpha        bool
+	emulationForwardCompatible              bool
+	runtimeConfigEmulationForwardCompatible bool
+	isAlpha                                 bool
 	// Special flag checking for the existence of alpha.0
 	// alpha.0 is a special case where everything merged to master is auto propagated to the release-1.n branch
 	isAlphaZero bool
@@ -50,20 +56,41 @@ type resourceExpirationEvaluator struct {
 
 // ResourceExpirationEvaluator indicates whether or not a resource should be served.
 type ResourceExpirationEvaluator interface {
-	// RemoveDeletedKinds inspects the storage map and modifies it in place by removing storage for kinds that have been deleted.
+	// RemoveUnavailableKinds inspects the storage map and modifies it in place by removing storage for kinds that have been deleted or are introduced after the current version.
 	// versionedResourcesStorageMap mirrors the field on APIGroupInfo, it's a map from version to resource to the storage.
-	RemoveDeletedKinds(groupName string, versioner runtime.ObjectVersioner, versionedResourcesStorageMap map[string]map[string]rest.Storage)
+	RemoveUnavailableKinds(groupName string, versioner runtime.ObjectVersioner, versionedResourcesStorageMap map[string]map[string]rest.Storage, apiResourceConfigSource serverstorage.APIResourceConfigSource) error
 	// ShouldServeForVersion returns true if a particular version cut off is after the current version
 	ShouldServeForVersion(majorRemoved, minorRemoved int) bool
 }
 
+type ResourceExpirationEvaluatorOptions struct {
+	// CurrentVersion is the current version of the apiserver.
+	CurrentVersion *apimachineryversion.Version
+	// EmulationForwardCompatible indicates whether the apiserver should serve resources that are introduced after the current version,
+	// when resources of the same group and resource name but with lower priority are served.
+	EmulationForwardCompatible bool
+	// RuntimeConfigEmulationForwardCompatible indicates whether the apiserver should serve resources that are introduced after the current version,
+	// when the resource is explicitly enabled in runtime-config.
+	RuntimeConfigEmulationForwardCompatible bool
+}
+
 func NewResourceExpirationEvaluator(currentVersion *apimachineryversion.Version) (ResourceExpirationEvaluator, error) {
+	opts := ResourceExpirationEvaluatorOptions{
+		CurrentVersion: currentVersion,
+	}
+	return NewResourceExpirationEvaluatorFromOptions(opts)
+}
+
+func NewResourceExpirationEvaluatorFromOptions(opts ResourceExpirationEvaluatorOptions) (ResourceExpirationEvaluator, error) {
+	currentVersion := opts.CurrentVersion
 	if currentVersion == nil {
 		return nil, fmt.Errorf("empty NewResourceExpirationEvaluator currentVersion")
 	}
 	klog.V(1).Infof("NewResourceExpirationEvaluator with currentVersion: %s.", currentVersion)
 	ret := &resourceExpirationEvaluator{
-		strictRemovedHandlingInAlpha: false,
+		strictRemovedHandlingInAlpha:            false,
+		emulationForwardCompatible:              opts.EmulationForwardCompatible,
+		runtimeConfigEmulationForwardCompatible: opts.RuntimeConfigEmulationForwardCompatible,
 	}
 	// Only keeps the major and minor versions from input version.
 	ret.currentVersion = apimachineryversion.MajorMinor(currentVersion.Major(), currentVersion.Minor())
@@ -89,7 +116,8 @@ func NewResourceExpirationEvaluator(currentVersion *apimachineryversion.Version)
 	return ret, nil
 }
 
-func (e *resourceExpirationEvaluator) shouldServe(gv schema.GroupVersion, versioner runtime.ObjectVersioner, resourceServingInfo rest.Storage) bool {
+// isNotRemoved checks if a resource is removed due to the APILifecycleRemoved information.
+func (e *resourceExpirationEvaluator) isNotRemoved(gv schema.GroupVersion, versioner runtime.ObjectVersioner, resourceServingInfo rest.Storage) bool {
 	internalPtr := resourceServingInfo.New()
 
 	target := gv
@@ -104,15 +132,6 @@ func (e *resourceExpirationEvaluator) shouldServe(gv schema.GroupVersion, versio
 		return false
 	}
 
-	introduced, ok := versionedPtr.(introducedInterface)
-	if ok {
-		majorIntroduced, minorIntroduced := introduced.APILifecycleIntroduced()
-		verIntroduced := apimachineryversion.MajorMinor(uint(majorIntroduced), uint(minorIntroduced))
-		if e.currentVersion.LessThan(verIntroduced) {
-			return false
-		}
-	}
-
 	removed, ok := versionedPtr.(removedInterface)
 	if !ok {
 		return true
@@ -155,13 +174,13 @@ type introducedInterface interface {
 
 // removeDeletedKinds inspects the storage map and modifies it in place by removing storage for kinds that have been deleted.
 // versionedResourcesStorageMap mirrors the field on APIGroupInfo, it's a map from version to resource to the storage.
-func (e *resourceExpirationEvaluator) RemoveDeletedKinds(groupName string, versioner runtime.ObjectVersioner, versionedResourcesStorageMap map[string]map[string]rest.Storage) {
+func (e *resourceExpirationEvaluator) removeDeletedKinds(groupName string, versioner runtime.ObjectVersioner, versionedResourcesStorageMap map[string]map[string]rest.Storage) {
 	versionsToRemove := sets.NewString()
 	for apiVersion := range sets.StringKeySet(versionedResourcesStorageMap) {
 		versionToResource := versionedResourcesStorageMap[apiVersion]
 		resourcesToRemove := sets.NewString()
 		for resourceName, resourceServingInfo := range versionToResource {
-			if !e.shouldServe(schema.GroupVersion{Group: groupName, Version: apiVersion}, versioner, resourceServingInfo) {
+			if !e.isNotRemoved(schema.GroupVersion{Group: groupName, Version: apiVersion}, versioner, resourceServingInfo) {
 				resourcesToRemove.Insert(resourceName)
 			}
 		}
@@ -189,6 +208,123 @@ func (e *resourceExpirationEvaluator) RemoveDeletedKinds(groupName string, versi
 	}
 }
 
+func (e *resourceExpirationEvaluator) RemoveUnavailableKinds(groupName string, versioner runtime.ObjectVersioner, versionedResourcesStorageMap map[string]map[string]rest.Storage, apiResourceConfigSource serverstorage.APIResourceConfigSource) error {
+	e.removeDeletedKinds(groupName, versioner, versionedResourcesStorageMap)
+	return e.removeUnintroducedKinds(groupName, versioner, versionedResourcesStorageMap, apiResourceConfigSource)
+}
+
+// removeUnintroducedKinds inspects the storage map and modifies it in place by removing storage for kinds that are introduced after the current version.
+// versionedResourcesStorageMap mirrors the field on APIGroupInfo, it's a map from version to resource to the storage.
+func (e *resourceExpirationEvaluator) removeUnintroducedKinds(groupName string, versioner runtime.ObjectVersioner, versionedResourcesStorageMap map[string]map[string]rest.Storage, apiResourceConfigSource serverstorage.APIResourceConfigSource) error {
+	versionsToRemove := sets.NewString()
+	prioritizedVersions := versioner.PrioritizedVersionsForGroup(groupName)
+	enabledResources := sets.NewString()
+
+	// iterate from the end to the front, so that we remove the lower priority versions first.
+	for i := len(prioritizedVersions) - 1; i >= 0; i-- {
+		apiVersion := prioritizedVersions[i].Version
+		versionToResource := versionedResourcesStorageMap[apiVersion]
+		if len(versionToResource) == 0 {
+			continue
+		}
+		resourcesToRemove := sets.NewString()
+		for resourceName, resourceServingInfo := range versionToResource {
+			// we check the resource enablement from low priority to high priority.
+			// If the same resource with a different version that we have checked so far is already enabled, that means some resource with the same resourceName and a lower priority version has been enabled.
+			// Then emulation forward compatibility for the version being checked now is made based on this information.
+			lowerPriorityEnabled := enabledResources.Has(resourceName)
+			shouldKeep, err := e.shouldServeBasedOnVersionIntroduced(schema.GroupVersionResource{Group: groupName, Version: apiVersion, Resource: resourceName},
+				versioner, resourceServingInfo, apiResourceConfigSource, lowerPriorityEnabled)
+			if err != nil {
+				return err
+			}
+			if !shouldKeep {
+				resourcesToRemove.Insert(resourceName)
+			} else if !alphaPattern.MatchString(apiVersion) {
+				// enabledResources is passed onto the next iteration to check the enablement of higher priority resources for emulation forward compatibility.
+				// But enablement alpha apis do not affect the enablement of other versions because emulation forward compatibility is not applicable to alpha apis.
+				enabledResources.Insert(resourceName)
+			}
+		}
+
+		for resourceName := range versionedResourcesStorageMap[apiVersion] {
+			if !shouldRemoveResourceAndSubresources(resourcesToRemove, resourceName) {
+				continue
+			}
+
+			klog.V(1).Infof("Removing resource %v.%v.%v because it is introduced after the current version %s per APILifecycle.", resourceName, apiVersion, groupName, e.currentVersion.String())
+			storage := versionToResource[resourceName]
+			storage.Destroy()
+			delete(versionToResource, resourceName)
+		}
+		versionedResourcesStorageMap[apiVersion] = versionToResource
+
+		if len(versionedResourcesStorageMap[apiVersion]) == 0 {
+			versionsToRemove.Insert(apiVersion)
+		}
+	}
+
+	for _, apiVersion := range versionsToRemove.List() {
+		gv := schema.GroupVersion{Group: groupName, Version: apiVersion}
+		if apiResourceConfigSource != nil && apiResourceConfigSource.VersionExplicitlyEnabled(gv) {
+			return fmt.Errorf(
+				"cannot enable version %s in runtime-config because all the resources have been introduced after the current version %s. Consider setting --runtime-config-emulation-forward-compatible=true",
+				gv, e.currentVersion)
+		}
+		klog.V(1).Infof("Removing version %v.%v because it is introduced after the current version %s and because it has no resources per APILifecycle.", apiVersion, groupName, e.currentVersion.String())
+		delete(versionedResourcesStorageMap, apiVersion)
+	}
+	return nil
+}
+
+func (e *resourceExpirationEvaluator) shouldServeBasedOnVersionIntroduced(gvr schema.GroupVersionResource, versioner runtime.ObjectVersioner, resourceServingInfo rest.Storage,
+	apiResourceConfigSource serverstorage.APIResourceConfigSource, lowerPriorityEnabled bool) (bool, error) {
+	verIntroduced := apimachineryversion.MajorMinor(0, 0)
+	internalPtr := resourceServingInfo.New()
+
+	target := gvr.GroupVersion()
+	// honor storage that overrides group version (used for things like scale subresources)
+	if versionProvider, ok := resourceServingInfo.(rest.GroupVersionKindProvider); ok {
+		target = versionProvider.GroupVersionKind(target).GroupVersion()
+	}
+
+	versionedPtr, err := versioner.ConvertToVersion(internalPtr, target)
+	if err != nil {
+		utilruntime.HandleError(err)
+		return false, err
+	}
+
+	introduced, ok := versionedPtr.(introducedInterface)
+	if ok {
+		majorIntroduced, minorIntroduced := introduced.APILifecycleIntroduced()
+		verIntroduced = apimachineryversion.MajorMinor(uint(majorIntroduced), uint(minorIntroduced))
+	}
+	// should serve resource introduced at or before the current version.
+	if e.currentVersion.AtLeast(verIntroduced) {
+		return true, nil
+	}
+	// the rest of the function is to determine if a resource introduced after current version should be served. (only applicable in emulation mode.)
+
+	// if a lower priority version of the resource has been enabled, the same resource with higher priority
+	// should also be enabled if emulationForwardCompatible = true.
+	if e.emulationForwardCompatible && lowerPriorityEnabled {
+		return true, nil
+	}
+	if apiResourceConfigSource == nil {
+		return false, nil
+	}
+	// could explicitly enable future resources in runtime-config forward compatible mode.
+	if e.runtimeConfigEmulationForwardCompatible && (apiResourceConfigSource.ResourceExplicitlyEnabled(gvr) || apiResourceConfigSource.VersionExplicitlyEnabled(gvr.GroupVersion())) {
+		return true, nil
+	}
+	// return error if a future resource is explicit enabled in runtime-config but runtimeConfigEmulationForwardCompatible is false.
+	if apiResourceConfigSource.ResourceExplicitlyEnabled(gvr) {
+		return false, fmt.Errorf("cannot enable resource %s in runtime-config because it is introduced at %s after the current version %s. Consider setting --runtime-config-emulation-forward-compatible=true",
+			gvr, verIntroduced, e.currentVersion)
+	}
+	return false, nil
+}
+
 func shouldRemoveResourceAndSubresources(resourcesToRemove sets.String, resourceName string) bool {
 	for _, resourceToRemove := range resourcesToRemove.List() {
 		if resourceName == resourceToRemove {

staging/src/k8s.io/apiserver/pkg/server/genericapiserver.go

@@ -245,6 +245,16 @@ type GenericAPIServer struct {
 	// EffectiveVersion determines which apis and features are available
 	// based on when the api/feature lifecyle.
 	EffectiveVersion basecompatibility.EffectiveVersion
+	// EmulationForwardCompatible is an option to implicitly enable all APIs which are introduced after the emulation version and
+	// have higher priority than APIs of the same group resource enabled at the emulation version.
+	// If true, all APIs that have higher priority than the APIs of the same group resource enabled at the emulation version will be installed.
+	// This is needed when a controller implementation migrates to newer API versions, for the binary version, and also uses the newer API versions even when emulation version is set.
+	EmulationForwardCompatible bool
+	// RuntimeConfigEmulationForwardCompatible is an option to explicitly enable specific APIs introduced after the emulation version through the runtime-config.
+	// If true, APIs identified by group/version that are enabled in the --runtime-config flag will be installed even if it is introduced after the emulation version. --runtime-config flag values that identify multiple APIs, such as api/all,api/ga,api/beta, are not influenced by this flag and will only enable APIs available at the current emulation version.
+	// If false, error would be thrown if any GroupVersion or GroupVersionResource explicitly enabled in the --runtime-config flag is introduced after the emulation version.
+	RuntimeConfigEmulationForwardCompatible bool
+
 	// FeatureGate is a way to plumb feature gate through if you have them.
 	FeatureGate featuregate.FeatureGate
 

staging/src/k8s.io/apiserver/pkg/server/options/api_enablement.go

@@ -95,6 +95,14 @@ func (s *APIEnablementOptions) ApplyTo(c *server.Config, defaultResourceConfig *
 	}
 
 	mergedResourceConfig, err := resourceconfig.MergeAPIResourceConfigs(defaultResourceConfig, s.RuntimeConfig, registry)
+	if err != nil {
+		return err
+	}
+	// apply emulation forward compatibility to the api enablement if applicable.
+	if c.EmulationForwardCompatible {
+		mergedResourceConfig, err = resourceconfig.EmulationForwardCompatibleResourceConfig(mergedResourceConfig, s.RuntimeConfig, registry)
+	}
+
 	c.MergedResourceConfig = mergedResourceConfig
 
 	return err

staging/src/k8s.io/apiserver/pkg/server/options/server_run_options.go

@@ -98,6 +98,15 @@ type ServerRunOptions struct {
 	ComponentGlobalsRegistry basecompatibility.ComponentGlobalsRegistry
 	// ComponentName is name under which the server's global variabled are registered in the ComponentGlobalsRegistry.
 	ComponentName string
+	// EmulationForwardCompatible is an option to implicitly enable all APIs which are introduced after the emulation version and
+	// have higher priority than APIs of the same group resource enabled at the emulation version.
+	// If true, all APIs that have higher priority than the APIs of the same group resource enabled at the emulation version will be installed.
+	// This is needed when a controller implementation migrates to newer API versions, for the binary version, and also uses the newer API versions even when emulation version is set.
+	EmulationForwardCompatible bool
+	// RuntimeConfigEmulationForwardCompatible is an option to explicitly enable specific APIs introduced after the emulation version through the runtime-config.
+	// If true, APIs identified by group/version that are enabled in the --runtime-config flag will be installed even if it is introduced after the emulation version. --runtime-config flag values that identify multiple APIs, such as api/all,api/ga,api/beta, are not influenced by this flag and will only enable APIs available at the current emulation version.
+	// If false, error would be thrown if any GroupVersion or GroupVersionResource explicitly enabled in the --runtime-config flag is introduced after the emulation version.
+	RuntimeConfigEmulationForwardCompatible bool
 }
 
 func NewServerRunOptions() *ServerRunOptions {
@@ -152,6 +161,8 @@ func (s *ServerRunOptions) ApplyTo(c *server.Config) error {
 	c.ShutdownWatchTerminationGracePeriod = s.ShutdownWatchTerminationGracePeriod
 	c.EffectiveVersion = s.ComponentGlobalsRegistry.EffectiveVersionFor(s.ComponentName)
 	c.FeatureGate = s.ComponentGlobalsRegistry.FeatureGateFor(s.ComponentName)
+	c.EmulationForwardCompatible = s.EmulationForwardCompatible
+	c.RuntimeConfigEmulationForwardCompatible = s.RuntimeConfigEmulationForwardCompatible
 
 	return nil
 }
@@ -231,6 +242,17 @@ func (s *ServerRunOptions) Validate() []error {
 	if errs := s.ComponentGlobalsRegistry.Validate(); len(errs) != 0 {
 		errors = append(errors, errs...)
 	}
+	effectiveVersion := s.ComponentGlobalsRegistry.EffectiveVersionFor(s.ComponentName)
+	if effectiveVersion == nil {
+		return errors
+	}
+	notEmulationMode := effectiveVersion.BinaryVersion().WithPatch(0).EqualTo(effectiveVersion.EmulationVersion())
+	if notEmulationMode && s.EmulationForwardCompatible {
+		errors = append(errors, fmt.Errorf("ServerRunOptions.EmulationForwardCompatible cannot be set to true if the emulation version is the same as the binary version"))
+	}
+	if notEmulationMode && s.RuntimeConfigEmulationForwardCompatible {
+		errors = append(errors, fmt.Errorf("ServerRunOptions.RuntimeConfigEmulationForwardCompatible cannot be set to true if the emulation version is the same as the binary version"))
+	}
 	return errors
 }
 
@@ -376,6 +398,12 @@ func (s *ServerRunOptions) AddUniversalFlags(fs *pflag.FlagSet) {
 		"for active watch request(s) to drain during the graceful server shutdown window.")
 
 	s.ComponentGlobalsRegistry.AddFlags(fs)
+	fs.BoolVar(&s.EmulationForwardCompatible, "emulation-forward-compatible", s.EmulationForwardCompatible, ""+
+		"If true all APIs that have higher priority than the APIs enabled at the emulation version of the same group resource will be installed. "+
+		"Can only be set to true if the emulation version is lower than the binary version.")
+	fs.BoolVar(&s.RuntimeConfigEmulationForwardCompatible, "runtime-config-emulation-forward-compatible", s.RuntimeConfigEmulationForwardCompatible, ""+
+		"If true, APIs identified by group/version that are enabled in the --runtime-config flag will be installed even if it is introduced after the emulation version. "+
+		"Can only be set to true if the emulation version is lower than the binary version.")
 }
 
 // Complete fills missing fields with defaults.

staging/src/k8s.io/apiserver/pkg/server/options/server_run_options_test.go

@@ -31,18 +31,12 @@ import (
 )
 
 func TestServerRunOptionsValidate(t *testing.T) {
-	defaultComponentGlobalsRegistry := basecompatibility.NewComponentGlobalsRegistry()
-	testRegistry := basecompatibility.NewComponentGlobalsRegistry()
-	featureGate := utilfeature.DefaultFeatureGate.DeepCopy()
-	effectiveVersion := basecompatibility.NewEffectiveVersionFromString("1.35", "1.32", "1.32")
-	effectiveVersion.SetEmulationVersion(version.MajorMinor(1, 31))
 	testComponent := "test"
-	utilruntime.Must(testRegistry.Register(testComponent, effectiveVersion, featureGate))
-
 	testCases := []struct {
-		name        string
+		name             string
-		testOptions *ServerRunOptions
+		testOptions      *ServerRunOptions
-		expectErr   string
+		emulationVersion string
+		expectErr        string
 	}{
 		{
 			name: "Test when MaxRequestsInFlight is negative value",
@@ -55,7 +49,8 @@ func TestServerRunOptionsValidate(t *testing.T) {
 				MinRequestTimeout:           1800,
 				JSONPatchMaxCopyBytes:       10 * 1024 * 1024,
 				MaxRequestBodyBytes:         10 * 1024 * 1024,
-				ComponentGlobalsRegistry:    defaultComponentGlobalsRegistry,
+				ComponentGlobalsRegistry:    newTestRegistry(testComponent),
+				ComponentName:               testComponent,
 			},
 			expectErr: "--max-requests-inflight can not be negative value",
 		},
@@ -70,7 +65,8 @@ func TestServerRunOptionsValidate(t *testing.T) {
 				MinRequestTimeout:           1800,
 				JSONPatchMaxCopyBytes:       10 * 1024 * 1024,
 				MaxRequestBodyBytes:         10 * 1024 * 1024,
-				ComponentGlobalsRegistry:    defaultComponentGlobalsRegistry,
+				ComponentGlobalsRegistry:    newTestRegistry(testComponent),
+				ComponentName:               testComponent,
 			},
 			expectErr: "--max-mutating-requests-inflight can not be negative value",
 		},
@@ -85,7 +81,8 @@ func TestServerRunOptionsValidate(t *testing.T) {
 				MinRequestTimeout:           1800,
 				JSONPatchMaxCopyBytes:       10 * 1024 * 1024,
 				MaxRequestBodyBytes:         10 * 1024 * 1024,
-				ComponentGlobalsRegistry:    defaultComponentGlobalsRegistry,
+				ComponentGlobalsRegistry:    newTestRegistry(testComponent),
+				ComponentName:               testComponent,
 			},
 			expectErr: "--request-timeout can not be negative value",
 		},
@@ -100,7 +97,8 @@ func TestServerRunOptionsValidate(t *testing.T) {
 				MinRequestTimeout:           -1800,
 				JSONPatchMaxCopyBytes:       10 * 1024 * 1024,
 				MaxRequestBodyBytes:         10 * 1024 * 1024,
-				ComponentGlobalsRegistry:    defaultComponentGlobalsRegistry,
+				ComponentGlobalsRegistry:    newTestRegistry(testComponent),
+				ComponentName:               testComponent,
 			},
 			expectErr: "--min-request-timeout can not be negative value",
 		},
@@ -115,7 +113,8 @@ func TestServerRunOptionsValidate(t *testing.T) {
 				MinRequestTimeout:           1800,
 				JSONPatchMaxCopyBytes:       -10 * 1024 * 1024,
 				MaxRequestBodyBytes:         10 * 1024 * 1024,
-				ComponentGlobalsRegistry:    defaultComponentGlobalsRegistry,
+				ComponentGlobalsRegistry:    newTestRegistry(testComponent),
+				ComponentName:               testComponent,
 			},
 			expectErr: "ServerRunOptions.JSONPatchMaxCopyBytes can not be negative value",
 		},
@@ -130,7 +129,8 @@ func TestServerRunOptionsValidate(t *testing.T) {
 				MinRequestTimeout:           1800,
 				JSONPatchMaxCopyBytes:       10 * 1024 * 1024,
 				MaxRequestBodyBytes:         -10 * 1024 * 1024,
-				ComponentGlobalsRegistry:    defaultComponentGlobalsRegistry,
+				ComponentGlobalsRegistry:    newTestRegistry(testComponent),
+				ComponentName:               testComponent,
 			},
 			expectErr: "ServerRunOptions.MaxRequestBodyBytes can not be negative value",
 		},
@@ -146,7 +146,8 @@ func TestServerRunOptionsValidate(t *testing.T) {
 				JSONPatchMaxCopyBytes:       10 * 1024 * 1024,
 				MaxRequestBodyBytes:         10 * 1024 * 1024,
 				LivezGracePeriod:            -time.Second,
-				ComponentGlobalsRegistry:    defaultComponentGlobalsRegistry,
+				ComponentGlobalsRegistry:    newTestRegistry(testComponent),
+				ComponentName:               testComponent,
 			},
 			expectErr: "--livez-grace-period can not be a negative value",
 		},
@@ -162,7 +163,8 @@ func TestServerRunOptionsValidate(t *testing.T) {
 				JSONPatchMaxCopyBytes:       10 * 1024 * 1024,
 				MaxRequestBodyBytes:         10 * 1024 * 1024,
 				ShutdownDelayDuration:       -time.Second,
-				ComponentGlobalsRegistry:    defaultComponentGlobalsRegistry,
+				ComponentGlobalsRegistry:    newTestRegistry(testComponent),
+				ComponentName:               testComponent,
 			},
 			expectErr: "--shutdown-delay-duration can not be negative value",
 		},
@@ -178,7 +180,8 @@ func TestServerRunOptionsValidate(t *testing.T) {
 				MinRequestTimeout:           1800,
 				JSONPatchMaxCopyBytes:       10 * 1024 * 1024,
 				MaxRequestBodyBytes:         10 * 1024 * 1024,
-				ComponentGlobalsRegistry:    defaultComponentGlobalsRegistry,
+				ComponentGlobalsRegistry:    newTestRegistry(testComponent),
+				ComponentName:               testComponent,
 			},
 			expectErr: "--strict-transport-security-directives invalid, allowed values: max-age=expireTime, includeSubDomains, preload. see https://tools.ietf.org/html/rfc6797#section-6.1 for more information",
 		},
@@ -195,9 +198,65 @@ func TestServerRunOptionsValidate(t *testing.T) {
 				JSONPatchMaxCopyBytes:       10 * 1024 * 1024,
 				MaxRequestBodyBytes:         10 * 1024 * 1024,
 				ComponentName:               testComponent,
-				ComponentGlobalsRegistry:    testRegistry,
+				ComponentGlobalsRegistry:    newTestRegistry(testComponent),
 			},
-			expectErr: "emulation version 1.31 is not between [1.32, 1.35.0]",
+			emulationVersion: "1.31",
+			expectErr:        "emulation version 1.31 is not between [1.32, 1.35.0]",
+		},
+		{
+			name: "Test EmulationForwardCompatible cannot be true if not in emulation mode",
+			testOptions: &ServerRunOptions{
+				AdvertiseAddress:            netutils.ParseIPSloppy("192.168.10.10"),
+				CorsAllowedOriginList:       []string{"^10.10.10.100$", "^10.10.10.200$"},
+				HSTSDirectives:              []string{"max-age=31536000", "includeSubDomains", "preload"},
+				MaxRequestsInFlight:         400,
+				MaxMutatingRequestsInFlight: 200,
+				RequestTimeout:              time.Duration(2) * time.Minute,
+				MinRequestTimeout:           1800,
+				JSONPatchMaxCopyBytes:       10 * 1024 * 1024,
+				MaxRequestBodyBytes:         10 * 1024 * 1024,
+				ComponentGlobalsRegistry:    newTestRegistry(testComponent),
+				ComponentName:               testComponent,
+				EmulationForwardCompatible:  true,
+			},
+			expectErr: "ServerRunOptions.EmulationForwardCompatible cannot be set to true if the emulation version is the same as the binary version",
+		},
+		{
+			name: "Test RuntimeConfigEmulationForwardCompatible cannot be true if not in emulation mode",
+			testOptions: &ServerRunOptions{
+				AdvertiseAddress:                        netutils.ParseIPSloppy("192.168.10.10"),
+				CorsAllowedOriginList:                   []string{"^10.10.10.100$", "^10.10.10.200$"},
+				HSTSDirectives:                          []string{"max-age=31536000", "includeSubDomains", "preload"},
+				MaxRequestsInFlight:                     400,
+				MaxMutatingRequestsInFlight:             200,
+				RequestTimeout:                          time.Duration(2) * time.Minute,
+				MinRequestTimeout:                       1800,
+				JSONPatchMaxCopyBytes:                   10 * 1024 * 1024,
+				MaxRequestBodyBytes:                     10 * 1024 * 1024,
+				ComponentGlobalsRegistry:                newTestRegistry(testComponent),
+				ComponentName:                           testComponent,
+				RuntimeConfigEmulationForwardCompatible: true,
+			},
+			expectErr: "ServerRunOptions.RuntimeConfigEmulationForwardCompatible cannot be set to true if the emulation version is the same as the binary version",
+		},
+		{
+			name: "Test EmulationForwardCompatible can be true if in emulation mode",
+			testOptions: &ServerRunOptions{
+				AdvertiseAddress:                        netutils.ParseIPSloppy("192.168.10.10"),
+				CorsAllowedOriginList:                   []string{"^10.10.10.100$", "^10.10.10.200$"},
+				HSTSDirectives:                          []string{"max-age=31536000", "includeSubDomains", "preload"},
+				MaxRequestsInFlight:                     400,
+				MaxMutatingRequestsInFlight:             200,
+				RequestTimeout:                          time.Duration(2) * time.Minute,
+				MinRequestTimeout:                       1800,
+				JSONPatchMaxCopyBytes:                   10 * 1024 * 1024,
+				MaxRequestBodyBytes:                     10 * 1024 * 1024,
+				ComponentGlobalsRegistry:                newTestRegistry(testComponent),
+				ComponentName:                           testComponent,
+				EmulationForwardCompatible:              true,
+				RuntimeConfigEmulationForwardCompatible: true,
+			},
+			emulationVersion: "1.34",
 		},
 		{
 			name: "Test when ServerRunOptions is valid",
@@ -211,13 +270,18 @@ func TestServerRunOptionsValidate(t *testing.T) {
 				MinRequestTimeout:           1800,
 				JSONPatchMaxCopyBytes:       10 * 1024 * 1024,
 				MaxRequestBodyBytes:         10 * 1024 * 1024,
-				ComponentGlobalsRegistry:    defaultComponentGlobalsRegistry,
+				ComponentGlobalsRegistry:    newTestRegistry(testComponent),
+				ComponentName:               testComponent,
 			},
 		},
 	}
 
 	for _, testcase := range testCases {
 		t.Run(testcase.name, func(t *testing.T) {
+			if testcase.emulationVersion != "" {
+				effectiveVersion := testcase.testOptions.ComponentGlobalsRegistry.EffectiveVersionFor(testcase.testOptions.ComponentName)
+				effectiveVersion.(basecompatibility.MutableEffectiveVersion).SetEmulationVersion(version.MustParse(testcase.emulationVersion))
+			}
 			errs := testcase.testOptions.Validate()
 			if len(testcase.expectErr) != 0 && !strings.Contains(utilerrors.NewAggregate(errs).Error(), testcase.expectErr) {
 				t.Errorf("got err: %v, expected err: %s", errs, testcase.expectErr)
@@ -230,6 +294,14 @@ func TestServerRunOptionsValidate(t *testing.T) {
 	}
 }
 
+func newTestRegistry(componentName string) basecompatibility.ComponentGlobalsRegistry {
+	registry := basecompatibility.NewComponentGlobalsRegistry()
+	featureGate := utilfeature.DefaultFeatureGate.DeepCopy()
+	effectiveVersion := basecompatibility.NewEffectiveVersionFromString("1.35", "1.32", "1.32")
+	utilruntime.Must(registry.Register(componentName, effectiveVersion, featureGate))
+	return registry
+}
+
 func TestValidateCorsAllowedOriginList(t *testing.T) {
 	tests := []struct {
 		regexp           [][]string

staging/src/k8s.io/apiserver/pkg/server/resourceconfig/helpers.go

@@ -36,6 +36,8 @@ type GroupVersionRegistry interface {
 	IsVersionRegistered(v schema.GroupVersion) bool
 	// PrioritizedVersionsAllGroups returns all registered group versions.
 	PrioritizedVersionsAllGroups() []schema.GroupVersion
+	// PrioritizedVersionsForGroup returns versions for a single group in priority order
+	PrioritizedVersionsForGroup(group string) []schema.GroupVersion
 }
 
 // MergeResourceEncodingConfigs merges the given defaultResourceConfig with specific GroupVersionResource overrides.
@@ -100,7 +102,17 @@ func MergeAPIResourceConfigs(
 			}
 		}
 	}
+	if err := applyVersionAndResourcePreferences(resourceConfig, overrides, registry); err != nil {
+		return nil, err
+	}
+	return resourceConfig, nil
+}
 
+func applyVersionAndResourcePreferences(
+	resourceConfig *serverstore.ResourceConfig,
+	overrides cliflag.ConfigurationMap,
+	registry GroupVersionRegistry,
+) error {
 	type versionEnablementPreference struct {
 		key          string
 		enabled      bool
@@ -130,7 +142,7 @@ func MergeAPIResourceConfigs(
 		groupVersionString := tokens[0] + "/" + tokens[1]
 		groupVersion, err := schema.ParseGroupVersion(groupVersionString)
 		if err != nil {
-			return nil, fmt.Errorf("invalid key %s", key)
+			return fmt.Errorf("invalid key %s", key)
 		}
 
 		// Exclude group not registered into the registry.
@@ -140,11 +152,11 @@ func MergeAPIResourceConfigs(
 
 		// Verify that the groupVersion is registered into registry.
 		if !registry.IsVersionRegistered(groupVersion) {
-			return nil, fmt.Errorf("group version %s that has not been registered", groupVersion.String())
+			return fmt.Errorf("group version %s that has not been registered", groupVersion.String())
 		}
 		enabled, err := getRuntimeConfigValue(overrides, key, false)
 		if err != nil {
-			return nil, err
+			return err
 		}
 
 		switch len(tokens) {
@@ -156,7 +168,7 @@ func MergeAPIResourceConfigs(
 			})
 		case 3:
 			if strings.ToLower(tokens[2]) != tokens[2] {
-				return nil, fmt.Errorf("invalid key %v: group/version/resource and resource is always lowercase plural, not %q", key, tokens[2])
+				return fmt.Errorf("invalid key %v: group/version/resource and resource is always lowercase plural, not %q", key, tokens[2])
 			}
 			resourcePreferences = append(resourcePreferences, resourceEnablementPreference{
 				key:                  key,
@@ -170,11 +182,11 @@ func MergeAPIResourceConfigs(
 	for _, versionPreference := range versionPreferences {
 		if versionPreference.enabled {
 			// enable the groupVersion for "group/version=true"
-			resourceConfig.EnableVersions(versionPreference.groupVersion)
+			resourceConfig.ExplicitlyEnableVersions(versionPreference.groupVersion)
 
 		} else {
 			// disable the groupVersion only for "group/version=false"
-			resourceConfig.DisableVersions(versionPreference.groupVersion)
+			resourceConfig.ExplicitlyDisableVersions(versionPreference.groupVersion)
 		}
 	}
 
@@ -182,13 +194,12 @@ func MergeAPIResourceConfigs(
 	for _, resourcePreference := range resourcePreferences {
 		if resourcePreference.enabled {
 			// enable the resource for "group/version/resource=true"
-			resourceConfig.EnableResources(resourcePreference.groupVersionResource)
+			resourceConfig.ExplicitlyEnableResources(resourcePreference.groupVersionResource)
 		} else {
-			resourceConfig.DisableResources(resourcePreference.groupVersionResource)
+			resourceConfig.ExplicitlyDisableResources(resourcePreference.groupVersionResource)
 		}
 	}
-
+	return nil
-	return resourceConfig, nil
 }
 
 func getRuntimeConfigValue(overrides cliflag.ConfigurationMap, apiKey string, defaultValue bool) (bool, error) {
@@ -227,3 +238,53 @@ func ParseGroups(resourceConfig cliflag.ConfigurationMap) ([]string, error) {
 
 	return groups, nil
 }
+
+// EmulationForwardCompatibleResourceConfig creates a new ResourceConfig that besides all the enabled resources in resourceConfig,
+// enables all higher priority versions of enabled resources, excluding alpha versions.
+// This is useful for ensuring forward compatibility when a new version of an API is introduced.
+func EmulationForwardCompatibleResourceConfig(
+	resourceConfig *serverstore.ResourceConfig,
+	resourceConfigOverrides cliflag.ConfigurationMap,
+	registry GroupVersionRegistry,
+) (*serverstore.ResourceConfig, error) {
+	ret := serverstore.NewResourceConfig()
+	for gv, enabled := range resourceConfig.GroupVersionConfigs {
+		ret.GroupVersionConfigs[gv] = enabled
+		if !enabled {
+			continue
+		}
+		// emulation forward compatibility is not applicable to alpha apis.
+		if alphaPattern.MatchString(gv.Version) {
+			continue
+		}
+		// if a gv is enabled, all the versions with higher priority (all the versions before gv in PrioritizedVersionsForGroup) are also implicitly enabled for emulation forward compatibility.
+		for _, pgv := range registry.PrioritizedVersionsForGroup(gv.Group) {
+			if pgv.Version == gv.Version {
+				break
+			}
+			ret.EnableVersions(pgv)
+		}
+	}
+	for gvr, enabled := range resourceConfig.ResourceConfigs {
+		ret.ResourceConfigs[gvr] = enabled
+		if !enabled {
+			continue
+		}
+		// emulation forward compatibility is not applicable to alpha apis.
+		if alphaPattern.MatchString(gvr.Version) {
+			continue
+		}
+		// if a gvr is enabled, all the versions with the same resource name and higher priority (all the versions before gv in PrioritizedVersionsForGroup) are also implicitly enabled for emulation forward compatibility.
+		for _, pgv := range registry.PrioritizedVersionsForGroup(gvr.Group) {
+			if pgv.Version == gvr.Version {
+				break
+			}
+			ret.EnableResources(pgv.WithResource(gvr.Resource))
+		}
+	}
+	// need to reapply the version preferences if there is an override of a higher priority version.
+	if err := applyVersionAndResourcePreferences(ret, resourceConfigOverrides, registry); err != nil {
+		return nil, err
+	}
+	return ret, nil
+}

staging/src/k8s.io/apiserver/pkg/server/resourceconfig/helpers_test.go

@@ -27,6 +27,7 @@ import (
 	extensionsapiv1beta1 "k8s.io/api/extensions/v1beta1"
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/runtime/schema"
+	runtimetesting "k8s.io/apimachinery/pkg/runtime/testing"
 	serverstore "k8s.io/apiserver/pkg/server/storage"
 )
 
@@ -50,7 +51,9 @@ func TestParseRuntimeConfig(t *testing.T) {
 				return newFakeAPIResourceConfigSource()
 			},
 			expectedAPIConfig: func() *serverstore.ResourceConfig {
-				return newFakeAPIResourceConfigSource()
+				config := newFakeAPIResourceConfigSource()
+				config.ExplicitlyEnableResources(appsv1.SchemeGroupVersion.WithResource("deployments"))
+				return config
 			},
 			expectedEnabledAPIs: defaultFakeEnabledResources(),
 			err:                 true,
@@ -101,6 +104,7 @@ func TestParseRuntimeConfig(t *testing.T) {
 			},
 			expectedAPIConfig: func() *serverstore.ResourceConfig {
 				config := newFakeAPIResourceConfigSource()
+				config.ExplicitlyEnableVersions(appsv1.SchemeGroupVersion)
 				return config
 			},
 			expectedEnabledAPIs: defaultFakeEnabledResources(),
@@ -116,7 +120,7 @@ func TestParseRuntimeConfig(t *testing.T) {
 			},
 			expectedAPIConfig: func() *serverstore.ResourceConfig {
 				config := newFakeAPIResourceConfigSource()
-				config.DisableVersions(apiv1GroupVersion)
+				config.ExplicitlyDisableVersions(apiv1GroupVersion)
 				return config
 			},
 			expectedEnabledAPIs: map[schema.GroupVersionResource]bool{
@@ -177,6 +181,7 @@ func TestParseRuntimeConfig(t *testing.T) {
 			},
 			expectedAPIConfig: func() *serverstore.ResourceConfig {
 				config := newFakeAPIResourceConfigSource()
+				config.ExplicitlyEnableVersions(apiv1GroupVersion)
 				config.DisableVersions(appsv1.SchemeGroupVersion)
 				config.DisableVersions(extensionsapiv1beta1.SchemeGroupVersion)
 				return config
@@ -201,7 +206,7 @@ func TestParseRuntimeConfig(t *testing.T) {
 			},
 			expectedAPIConfig: func() *serverstore.ResourceConfig {
 				config := newFakeAPIResourceConfigSource()
-				config.EnableResources(extensionsapiv1beta1.SchemeGroupVersion.WithResource("deployments"))
+				config.ExplicitlyEnableResources(extensionsapiv1beta1.SchemeGroupVersion.WithResource("deployments"))
 				return config
 			},
 			expectedEnabledAPIs: map[schema.GroupVersionResource]bool{
@@ -223,7 +228,7 @@ func TestParseRuntimeConfig(t *testing.T) {
 			},
 			expectedAPIConfig: func() *serverstore.ResourceConfig {
 				config := newFakeAPIResourceConfigSource()
-				config.DisableResources(extensionsapiv1beta1.SchemeGroupVersion.WithResource("ingresses"))
+				config.ExplicitlyDisableResources(extensionsapiv1beta1.SchemeGroupVersion.WithResource("ingresses"))
 				return config
 			},
 			expectedEnabledAPIs: map[schema.GroupVersionResource]bool{
@@ -245,7 +250,7 @@ func TestParseRuntimeConfig(t *testing.T) {
 			},
 			expectedAPIConfig: func() *serverstore.ResourceConfig {
 				config := newFakeAPIResourceConfigSource()
-				config.DisableVersions(extensionsapiv1beta1.SchemeGroupVersion)
+				config.ExplicitlyDisableVersions(extensionsapiv1beta1.SchemeGroupVersion)
 				return config
 			},
 			expectedEnabledAPIs: map[schema.GroupVersionResource]bool{
@@ -267,7 +272,7 @@ func TestParseRuntimeConfig(t *testing.T) {
 			},
 			expectedAPIConfig: func() *serverstore.ResourceConfig {
 				config := newFakeAPIResourceConfigSource()
-				config.DisableResources(appsv1.SchemeGroupVersion.WithResource("deployments"))
+				config.ExplicitlyDisableResources(appsv1.SchemeGroupVersion.WithResource("deployments"))
 				return config
 			},
 			expectedEnabledAPIs: map[schema.GroupVersionResource]bool{
@@ -314,7 +319,8 @@ func TestParseRuntimeConfig(t *testing.T) {
 			},
 			expectedAPIConfig: func() *serverstore.ResourceConfig {
 				config := newFakeAPIResourceConfigSource()
-				config.DisableResources(appsv1.SchemeGroupVersion.WithResource("deployments"))
+				config.ExplicitlyEnableVersions(appsv1.SchemeGroupVersion)
+				config.ExplicitlyDisableResources(appsv1.SchemeGroupVersion.WithResource("deployments"))
 				return config
 			},
 			expectedEnabledAPIs: map[schema.GroupVersionResource]bool{
@@ -338,8 +344,8 @@ func TestParseRuntimeConfig(t *testing.T) {
 			},
 			expectedAPIConfig: func() *serverstore.ResourceConfig {
 				config := newFakeAPIResourceConfigSource()
-				config.DisableVersions(appsv1.SchemeGroupVersion)
+				config.ExplicitlyDisableVersions(appsv1.SchemeGroupVersion)
-				config.EnableResources(appsv1.SchemeGroupVersion.WithResource("deployments"))
+				config.ExplicitlyEnableResources(appsv1.SchemeGroupVersion.WithResource("deployments"))
 				return config
 			},
 			expectedEnabledAPIs: map[schema.GroupVersionResource]bool{
@@ -364,7 +370,7 @@ func TestParseRuntimeConfig(t *testing.T) {
 			},
 			expectedAPIConfig: func() *serverstore.ResourceConfig {
 				config := newFakeAPIResourceConfigSource()
-				config.DisableResources(appsv1.SchemeGroupVersion.WithResource("deployments"))
+				config.ExplicitlyDisableResources(appsv1.SchemeGroupVersion.WithResource("deployments"))
 				return config
 			},
 			expectedEnabledAPIs: map[schema.GroupVersionResource]bool{
@@ -390,7 +396,7 @@ func TestParseRuntimeConfig(t *testing.T) {
 				config := newFakeAPIResourceConfigSource()
 				config.DisableVersions(apiv1.SchemeGroupVersion)
 				config.DisableVersions(appsv1.SchemeGroupVersion)
-				config.EnableResources(appsv1.SchemeGroupVersion.WithResource("deployments"))
+				config.ExplicitlyEnableResources(appsv1.SchemeGroupVersion.WithResource("deployments"))
 				return config
 			},
 			expectedEnabledAPIs: map[schema.GroupVersionResource]bool{
@@ -416,8 +422,8 @@ func TestParseRuntimeConfig(t *testing.T) {
 			expectedAPIConfig: func() *serverstore.ResourceConfig {
 				config := newFakeAPIResourceConfigSource()
 				config.DisableVersions(apiv1.SchemeGroupVersion)
-				config.EnableVersions(appsv1.SchemeGroupVersion)
+				config.ExplicitlyEnableVersions(appsv1.SchemeGroupVersion)
-				config.DisableResources(appsv1.SchemeGroupVersion.WithResource("deployments"))
+				config.ExplicitlyDisableResources(appsv1.SchemeGroupVersion.WithResource("deployments"))
 				return config
 			},
 			expectedEnabledAPIs: map[schema.GroupVersionResource]bool{
@@ -444,8 +450,8 @@ func TestParseRuntimeConfig(t *testing.T) {
 			expectedAPIConfig: func() *serverstore.ResourceConfig {
 				config := newFakeAPIResourceConfigSource()
 				config.DisableVersions(apiv1.SchemeGroupVersion)
-				config.DisableVersions(appsv1.SchemeGroupVersion)
+				config.ExplicitlyDisableVersions(appsv1.SchemeGroupVersion)
-				config.EnableResources(appsv1.SchemeGroupVersion.WithResource("deployments"))
+				config.ExplicitlyEnableResources(appsv1.SchemeGroupVersion.WithResource("deployments"))
 				return config
 			},
 			expectedEnabledAPIs: map[schema.GroupVersionResource]bool{
@@ -470,8 +476,8 @@ func TestParseRuntimeConfig(t *testing.T) {
 			},
 			expectedAPIConfig: func() *serverstore.ResourceConfig {
 				config := newFakeAPIResourceConfigSource()
-				config.EnableVersions(appsv1.SchemeGroupVersion)
+				config.ExplicitlyEnableVersions(appsv1.SchemeGroupVersion)
-				config.DisableResources(appsv1.SchemeGroupVersion.WithResource("deployments"))
+				config.ExplicitlyDisableResources(appsv1.SchemeGroupVersion.WithResource("deployments"))
 				return config
 			},
 			expectedEnabledAPIs: map[schema.GroupVersionResource]bool{
@@ -496,8 +502,8 @@ func TestParseRuntimeConfig(t *testing.T) {
 			},
 			expectedAPIConfig: func() *serverstore.ResourceConfig {
 				config := newFakeAPIResourceConfigSource()
-				config.DisableVersions(appsv1.SchemeGroupVersion)
+				config.ExplicitlyDisableVersions(appsv1.SchemeGroupVersion)
-				config.EnableResources(appsv1.SchemeGroupVersion.WithResource("deployments"))
+				config.ExplicitlyEnableResources(appsv1.SchemeGroupVersion.WithResource("deployments"))
 				return config
 			},
 			expectedEnabledAPIs: map[schema.GroupVersionResource]bool{
@@ -547,6 +553,186 @@ func TestParseRuntimeConfig(t *testing.T) {
 	}
 }
 
+func TestEmulationForwardCompatibleResourceConfig(t *testing.T) {
+	scheme := newFakeScheme(t)
+	addTestGVs(t, scheme)
+	testGroup := "test"
+	v1 := schema.GroupVersion{Group: testGroup, Version: "v1"}
+	v2alpha1 := schema.GroupVersion{Group: "test", Version: "v2alpha1"}
+	v2beta1 := schema.GroupVersion{Group: testGroup, Version: "v2beta1"}
+	v2beta2 := schema.GroupVersion{Group: testGroup, Version: "v2beta2"}
+	v2 := schema.GroupVersion{Group: testGroup, Version: "v2"}
+
+	testCases := []struct {
+		name                    string
+		resourceConfig          func() *serverstore.ResourceConfig
+		resourceConfigOverrides map[string]string
+		expectedAPIConfig       func() *serverstore.ResourceConfig
+		err                     bool
+	}{
+		{
+			name: "emulation-forward-compatible-enabled-no-higher-priority",
+			resourceConfig: func() *serverstore.ResourceConfig {
+				config := serverstore.NewResourceConfig()
+				config.EnableVersions(v2)
+				return config
+			},
+			resourceConfigOverrides: map[string]string{},
+			expectedAPIConfig: func() *serverstore.ResourceConfig {
+				config := serverstore.NewResourceConfig()
+				config.EnableVersions(v2)
+				return config
+			},
+			err: false,
+		},
+		{
+			name: "emulation-forward-compatible-alpha-version",
+			resourceConfig: func() *serverstore.ResourceConfig {
+				config := serverstore.NewResourceConfig()
+				config.EnableVersions(v2alpha1)
+				return config
+			},
+			resourceConfigOverrides: map[string]string{},
+			expectedAPIConfig: func() *serverstore.ResourceConfig {
+				config := serverstore.NewResourceConfig()
+				config.EnableVersions(v2alpha1)
+				return config
+			},
+			err: false,
+		},
+		{
+			name: "emulation-forward-compatible-enabled-higher-priority-ga",
+			resourceConfig: func() *serverstore.ResourceConfig {
+				config := serverstore.NewResourceConfig()
+				config.EnableVersions(v1)
+				return config
+			},
+			resourceConfigOverrides: map[string]string{},
+			expectedAPIConfig: func() *serverstore.ResourceConfig {
+				config := serverstore.NewResourceConfig()
+				config.EnableVersions(v1, v2)
+				return config
+			},
+			err: false,
+		},
+		{
+			name: "emulation-forward-compatible-enabled-higher-priority",
+			resourceConfig: func() *serverstore.ResourceConfig {
+				config := serverstore.NewResourceConfig()
+				config.EnableVersions(v2beta1)
+				return config
+			},
+			resourceConfigOverrides: map[string]string{},
+			expectedAPIConfig: func() *serverstore.ResourceConfig {
+				config := serverstore.NewResourceConfig()
+				config.EnableVersions(v2beta1, v2beta2, v1, v2)
+				return config
+			},
+			err: false,
+		},
+		{
+			name: "emulation-forward-compatible-enabled-higher-priority-with-override",
+			resourceConfig: func() *serverstore.ResourceConfig {
+				config := serverstore.NewResourceConfig()
+				config.EnableVersions(v2beta1)
+				return config
+			},
+			resourceConfigOverrides: map[string]string{
+				"test/v2beta2": "false",
+			},
+			expectedAPIConfig: func() *serverstore.ResourceConfig {
+				config := serverstore.NewResourceConfig()
+				config.EnableVersions(v2beta1, v1, v2)
+				config.ExplicitlyDisableVersions(v2beta2)
+				return config
+			},
+			err: false,
+		},
+		{
+			name: "emulation-forward-compatible-enabled-resource-no-higher-priority",
+			resourceConfig: func() *serverstore.ResourceConfig {
+				config := serverstore.NewResourceConfig()
+				config.EnableResources(v2.WithResource("testtype1"))
+				return config
+			},
+			resourceConfigOverrides: map[string]string{},
+			expectedAPIConfig: func() *serverstore.ResourceConfig {
+				config := serverstore.NewResourceConfig()
+				config.EnableResources(v2.WithResource("testtype1"))
+				return config
+			},
+			err: false,
+		},
+		{
+			name: "emulation-forward-compatible-alpha-resource",
+			resourceConfig: func() *serverstore.ResourceConfig {
+				config := serverstore.NewResourceConfig()
+				config.EnableResources(v2alpha1.WithResource("testtype1"))
+				return config
+			},
+			resourceConfigOverrides: map[string]string{},
+			expectedAPIConfig: func() *serverstore.ResourceConfig {
+				config := serverstore.NewResourceConfig()
+				config.EnableResources(v2alpha1.WithResource("testtype1"))
+				return config
+			},
+			err: false,
+		},
+		{
+			name: "emulation-forward-compatible-enabled-resource-higher-priority",
+			resourceConfig: func() *serverstore.ResourceConfig {
+				config := serverstore.NewResourceConfig()
+				config.EnableResources(v2beta1.WithResource("testtype1"))
+				return config
+			},
+			resourceConfigOverrides: map[string]string{},
+			expectedAPIConfig: func() *serverstore.ResourceConfig {
+				config := serverstore.NewResourceConfig()
+				config.EnableResources(v2beta1.WithResource("testtype1"), v2beta2.WithResource("testtype1"), v1.WithResource("testtype1"), v2.WithResource("testtype1"))
+				return config
+			},
+			err: false,
+		},
+		{
+			name: "emulation-forward-compatible-enabled-resource-higher-priority-with-override",
+			resourceConfig: func() *serverstore.ResourceConfig {
+				config := serverstore.NewResourceConfig()
+				config.EnableResources(v2beta1.WithResource("testtype1"))
+				return config
+			},
+			resourceConfigOverrides: map[string]string{
+				"test/v2beta2/testtype1": "false",
+			},
+			expectedAPIConfig: func() *serverstore.ResourceConfig {
+				config := serverstore.NewResourceConfig()
+				config.EnableResources(v2beta1.WithResource("testtype1"), v1.WithResource("testtype1"), v2.WithResource("testtype1"))
+				config.ExplicitlyDisableResources(v2beta2.WithResource("testtype1"))
+				return config
+			},
+			err: false,
+		},
+	}
+
+	for _, test := range testCases {
+		t.Run(test.name, func(t *testing.T) {
+			actualAPIConfig, err := EmulationForwardCompatibleResourceConfig(test.resourceConfig(), test.resourceConfigOverrides, scheme)
+			if err == nil && test.err {
+				t.Fatalf("expected error")
+			} else if err != nil && !test.err {
+				t.Fatalf("unexpected error: %s, for test: %v", err, test)
+			}
+			if err != nil {
+				return
+			}
+
+			expectedConfig := test.expectedAPIConfig()
+			if !reflect.DeepEqual(actualAPIConfig, expectedConfig) {
+				t.Fatalf("unexpected apiResourceConfig. Actual: %v\n expected: %v", actualAPIConfig, expectedConfig)
+			}
+		})
+	}
+}
+
 func newFakeAPIResourceConfigSource() *serverstore.ResourceConfig {
 	ret := serverstore.NewResourceConfig()
 	// NOTE: GroupVersions listed here will be enabled by default. Don't put alpha versions in the list.
@@ -601,3 +787,20 @@ func newFakeScheme(t *testing.T) *runtime.Scheme {
 
 	return ret
 }
+
+func addTestGVs(t *testing.T, s *runtime.Scheme) {
+	v1 := schema.GroupVersion{Group: "test", Version: "v1"}
+	v2alpha1 := schema.GroupVersion{Group: "test", Version: "v2alpha1"}
+	v2beta1 := schema.GroupVersion{Group: "test", Version: "v2beta1"}
+	v2beta2 := schema.GroupVersion{Group: "test", Version: "v2beta2"}
+	v2 := schema.GroupVersion{Group: "test", Version: "v2"}
+
+	s.AddKnownTypes(v1, &runtimetesting.TestType1{})
+	s.AddKnownTypes(v2alpha1, &runtimetesting.TestType1{})
+	s.AddKnownTypes(v2beta1, &runtimetesting.TestType1{})
+	s.AddKnownTypes(v2beta2, &runtimetesting.TestType1{}, &runtimetesting.TestType2{})
+	s.AddKnownTypes(v2, &runtimetesting.TestType1{}, &runtimetesting.TestType2{})
+
+	require.NoError(t, runtimetesting.RegisterConversions(s))
+	require.NoError(t, s.SetVersionPriority(v2, v1, v2beta2, v2beta1))
+}

staging/src/k8s.io/apiserver/pkg/server/storage/resource_config.go

@@ -24,17 +24,26 @@ import (
 type APIResourceConfigSource interface {
 	ResourceEnabled(resource schema.GroupVersionResource) bool
 	AnyResourceForGroupEnabled(group string) bool
+	ResourceExplicitlyEnabled(resource schema.GroupVersionResource) bool
+	VersionExplicitlyEnabled(version schema.GroupVersion) bool
 }
 
 var _ APIResourceConfigSource = &ResourceConfig{}
 
 type ResourceConfig struct {
-	GroupVersionConfigs map[schema.GroupVersion]bool
+	GroupVersionConfigs         map[schema.GroupVersion]bool
-	ResourceConfigs     map[schema.GroupVersionResource]bool
+	ResourceConfigs             map[schema.GroupVersionResource]bool
+	ExplicitGroupVersionConfigs map[schema.GroupVersion]bool
+	ExplicitResourceConfigs     map[schema.GroupVersionResource]bool
 }
 
 func NewResourceConfig() *ResourceConfig {
-	return &ResourceConfig{GroupVersionConfigs: map[schema.GroupVersion]bool{}, ResourceConfigs: map[schema.GroupVersionResource]bool{}}
+	return &ResourceConfig{
+		GroupVersionConfigs:         map[schema.GroupVersion]bool{},
+		ResourceConfigs:             map[schema.GroupVersionResource]bool{},
+		ExplicitGroupVersionConfigs: map[schema.GroupVersion]bool{},
+		ExplicitResourceConfigs:     map[schema.GroupVersionResource]bool{},
+	}
 }
 
 // DisableMatchingVersions disables all group/versions for which the matcher function returns true.
@@ -77,6 +86,7 @@ func (o *ResourceConfig) removeMatchingResourcePreferences(matcher func(gvr sche
 	}
 	for _, k := range keysToRemove {
 		delete(o.ResourceConfigs, k)
+		delete(o.ExplicitResourceConfigs, k)
 	}
 }
 
@@ -91,6 +101,13 @@ func (o *ResourceConfig) DisableVersions(versions ...schema.GroupVersion) {
 	}
 }
 
+func (o *ResourceConfig) ExplicitlyDisableVersions(versions ...schema.GroupVersion) {
+	for _, version := range versions {
+		o.ExplicitGroupVersionConfigs[version] = false
+	}
+	o.DisableVersions(versions...)
+}
+
 // EnableVersions enables all resources in a given groupVersion.
 // This will remove any preferences previously set on individual resources.
 func (o *ResourceConfig) EnableVersions(versions ...schema.GroupVersion) {
@@ -103,10 +120,16 @@ func (o *ResourceConfig) EnableVersions(versions ...schema.GroupVersion) {
 
 }
 
+func (o *ResourceConfig) ExplicitlyEnableVersions(versions ...schema.GroupVersion) {
+	for _, version := range versions {
+		o.ExplicitGroupVersionConfigs[version] = true
+	}
+	o.EnableVersions(versions...)
+}
+
 // TODO this must be removed and we enable/disable individual resources.
 func (o *ResourceConfig) versionEnabled(version schema.GroupVersion) bool {
-	enabled, _ := o.GroupVersionConfigs[version]
+	return o.GroupVersionConfigs[version]
-	return enabled
 }
 
 func (o *ResourceConfig) DisableResources(resources ...schema.GroupVersionResource) {
@@ -115,12 +138,26 @@ func (o *ResourceConfig) DisableResources(resources ...schema.GroupVersionResour
 	}
 }
 
+func (o *ResourceConfig) ExplicitlyDisableResources(resources ...schema.GroupVersionResource) {
+	for _, resource := range resources {
+		o.ExplicitResourceConfigs[resource] = false
+	}
+	o.DisableResources(resources...)
+}
+
 func (o *ResourceConfig) EnableResources(resources ...schema.GroupVersionResource) {
 	for _, resource := range resources {
 		o.ResourceConfigs[resource] = true
 	}
 }
 
+func (o *ResourceConfig) ExplicitlyEnableResources(resources ...schema.GroupVersionResource) {
+	for _, resource := range resources {
+		o.ExplicitResourceConfigs[resource] = true
+	}
+	o.EnableResources(resources...)
+}
+
 func (o *ResourceConfig) ResourceEnabled(resource schema.GroupVersionResource) bool {
 	// if a resource is explicitly set, that takes priority over the preference of the version.
 	resourceEnabled, explicitlySet := o.ResourceConfigs[resource]
@@ -151,3 +188,19 @@ func (o *ResourceConfig) AnyResourceForGroupEnabled(group string) bool {
 
 	return false
 }
+
+func (o *ResourceConfig) ResourceExplicitlyEnabled(resource schema.GroupVersionResource) bool {
+	resourceEnabled, explicitlySet := o.ExplicitResourceConfigs[resource]
+	if explicitlySet {
+		return resourceEnabled
+	}
+	return false
+}
+
+func (o *ResourceConfig) VersionExplicitlyEnabled(version schema.GroupVersion) bool {
+	versionEnabled, explicitlySet := o.ExplicitGroupVersionConfigs[version]
+	if explicitlySet {
+		return versionEnabled
+	}
+	return false
+}

test/integration/apiserver/apiserver_test.go

@@ -261,7 +261,7 @@ func TestCacheControl(t *testing.T) {
 	}
 	for _, path := range paths {
 		t.Run(path, func(t *testing.T) {
-			req, err := http.NewRequest("GET", server.ClientConfig.Host+path, nil)
+			req, err := http.NewRequest(http.MethodGet, server.ClientConfig.Host+path, nil)
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -307,7 +307,7 @@ func TestHSTS(t *testing.T) {
 	}
 	for _, path := range paths {
 		t.Run(path, func(t *testing.T) {
-			req, err := http.NewRequest("GET", server.ClientConfig.Host+path, nil)
+			req, err := http.NewRequest(http.MethodGet, server.ClientConfig.Host+path, nil)
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -3328,7 +3328,7 @@ func TestAllowedEmulationVersions(t *testing.T) {
 				t.Fatal(err)
 			}
 
-			req, err := http.NewRequest("GET", server.ClientConfig.Host+"/", nil)
+			req, err := http.NewRequest(http.MethodGet, server.ClientConfig.Host+"/", nil)
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -3348,9 +3348,9 @@ func TestAllowedEmulationVersions(t *testing.T) {
 }
 
 func TestEnableEmulationVersion(t *testing.T) {
-	featuregatetesting.SetFeatureGateEmulationVersionDuringTest(t, utilfeature.DefaultFeatureGate, version.MustParse("1.32"))
+	featuregatetesting.SetFeatureGateEmulationVersionDuringTest(t, utilfeature.DefaultFeatureGate, version.MustParse("1.33"))
 	server := kubeapiservertesting.StartTestServerOrDie(t,
-		&kubeapiservertesting.TestServerInstanceOptions{BinaryVersion: "1.32"},
+		&kubeapiservertesting.TestServerInstanceOptions{BinaryVersion: "1.33"},
 		[]string{"--emulated-version=kube=1.31", "--runtime-config=api/beta=true"}, framework.SharedEtcd())
 	defer server.TearDownFn()
 
@@ -3376,22 +3376,146 @@ func TestEnableEmulationVersion(t *testing.T) {
 			expectedStatusCode: 200,
 		},
 		{
-			path:               "/apis/flowcontrol.apiserver.k8s.io/v1beta1/flowschemas", // introduced at 1.20, removed at 1.26
+			path:               "/apis/flowcontrol.apiserver.k8s.io/v1beta3/flowschemas", // introduced at 1.26, removed at 1.32
-			expectedStatusCode: 404,
+			expectedStatusCode: 200,
 		},
 		{
-			path:               "/apis/flowcontrol.apiserver.k8s.io/v1beta2/flowschemas", // introduced at 1.23, removed at 1.29
+			path:               "/apis/networking.k8s.io/v1beta1/servicecidrs", // introduced at 1.31, removed at 1.34
+			expectedStatusCode: 200,
+		},
+		{
+			path:               "/apis/networking.k8s.io/v1/servicecidrs", // introduced at 1.33
 			expectedStatusCode: 404,
 		},
+	}
+
+	for _, tc := range tcs {
+		t.Run(tc.path, func(t *testing.T) {
+			req, err := http.NewRequest(http.MethodGet, server.ClientConfig.Host+tc.path, nil)
+			if err != nil {
+				t.Fatal(err)
+			}
+			resp, err := rt.RoundTrip(req)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if resp.StatusCode != tc.expectedStatusCode {
+				t.Errorf("expect status code: %d, got : %d\n", tc.expectedStatusCode, resp.StatusCode)
+			}
+			defer func() {
+				_ = resp.Body.Close()
+			}()
+		})
+	}
+}
+
+func TestEnableEmulationVersionForwardCompatible(t *testing.T) {
+	featuregatetesting.SetFeatureGateEmulationVersionDuringTest(t, utilfeature.DefaultFeatureGate, version.MustParse("1.33"))
+	server := kubeapiservertesting.StartTestServerOrDie(t,
+		&kubeapiservertesting.TestServerInstanceOptions{BinaryVersion: "1.33"},
+		[]string{"--emulated-version=kube=1.31", "--runtime-config=api/beta=true", "--emulation-forward-compatible=true"}, framework.SharedEtcd())
+	defer server.TearDownFn()
+
+	rt, err := restclient.TransportFor(server.ClientConfig)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	tcs := []struct {
+		path               string
+		expectedStatusCode int
+	}{
+		{
+			path:               "/",
+			expectedStatusCode: 200,
+		},
+		{
+			path:               "/apis/apps/v1/deployments",
+			expectedStatusCode: 200,
+		},
+		{
+			path:               "/apis/flowcontrol.apiserver.k8s.io/v1/flowschemas",
+			expectedStatusCode: 200,
+		},
 		{
 			path:               "/apis/flowcontrol.apiserver.k8s.io/v1beta3/flowschemas", // introduced at 1.26, removed at 1.32
 			expectedStatusCode: 200,
 		},
+		{
+			path:               "/apis/networking.k8s.io/v1beta1/servicecidrs", // introduced at 1.31, removed at 1.34
+			expectedStatusCode: 200,
+		},
+		{
+			path:               "/apis/networking.k8s.io/v1/servicecidrs", // introduced at 1.33
+			expectedStatusCode: 200,
+		},
 	}
 
 	for _, tc := range tcs {
 		t.Run(tc.path, func(t *testing.T) {
-			req, err := http.NewRequest("GET", server.ClientConfig.Host+tc.path, nil)
+			req, err := http.NewRequest(http.MethodGet, server.ClientConfig.Host+tc.path, nil)
+			if err != nil {
+				t.Fatal(err)
+			}
+			resp, err := rt.RoundTrip(req)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if resp.StatusCode != tc.expectedStatusCode {
+				t.Errorf("expect status code: %d, got : %d\n", tc.expectedStatusCode, resp.StatusCode)
+			}
+			defer func() {
+				_ = resp.Body.Close()
+			}()
+		})
+	}
+}
+
+func TestEnableRuntimeConfigEmulationVersionForwardCompatible(t *testing.T) {
+	featuregatetesting.SetFeatureGateEmulationVersionDuringTest(t, utilfeature.DefaultFeatureGate, version.MustParse("1.33"))
+	server := kubeapiservertesting.StartTestServerOrDie(t,
+		&kubeapiservertesting.TestServerInstanceOptions{BinaryVersion: "1.33"},
+		[]string{"--emulated-version=kube=1.31", "--runtime-config-emulation-forward-compatible=true", "--runtime-config=api/beta=true,networking.k8s.io/v1=true"}, framework.SharedEtcd())
+	defer server.TearDownFn()
+
+	rt, err := restclient.TransportFor(server.ClientConfig)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	tcs := []struct {
+		path               string
+		expectedStatusCode int
+	}{
+		{
+			path:               "/",
+			expectedStatusCode: 200,
+		},
+		{
+			path:               "/apis/apps/v1/deployments",
+			expectedStatusCode: 200,
+		},
+		{
+			path:               "/apis/flowcontrol.apiserver.k8s.io/v1/flowschemas",
+			expectedStatusCode: 200,
+		},
+		{
+			path:               "/apis/flowcontrol.apiserver.k8s.io/v1beta3/flowschemas", // introduced at 1.26, removed at 1.32
+			expectedStatusCode: 200,
+		},
+		{
+			path:               "/apis/networking.k8s.io/v1beta1/servicecidrs", // introduced at 1.31, removed at 1.34
+			expectedStatusCode: 200,
+		},
+		{
+			path:               "/apis/networking.k8s.io/v1/servicecidrs", // introduced at 1.33
+			expectedStatusCode: 200,
+		},
+	}
+
+	for _, tc := range tcs {
+		t.Run(tc.path, func(t *testing.T) {
+			req, err := http.NewRequest(http.MethodGet, server.ClientConfig.Host+tc.path, nil)
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -3437,14 +3561,6 @@ func TestDisableEmulationVersion(t *testing.T) {
 			path:               "/apis/flowcontrol.apiserver.k8s.io/v1/flowschemas",
 			expectedStatusCode: 200,
 		},
-		{
-			path:               "/apis/flowcontrol.apiserver.k8s.io/v1beta1/flowschemas", // introduced at 1.20, removed at 1.26
-			expectedStatusCode: 404,
-		},
-		{
-			path:               "/apis/flowcontrol.apiserver.k8s.io/v1beta2/flowschemas", // introduced at 1.23, removed at 1.29
-			expectedStatusCode: 404,
-		},
 		{
 			path:               "/apis/flowcontrol.apiserver.k8s.io/v1beta3/flowschemas", // introduced at 1.26, removed at 1.32
 			expectedStatusCode: 404,
@@ -3453,7 +3569,7 @@ func TestDisableEmulationVersion(t *testing.T) {
 
 	for _, tc := range tcs {
 		t.Run(tc.path, func(t *testing.T) {
-			req, err := http.NewRequest("GET", server.ClientConfig.Host+tc.path, nil)
+			req, err := http.NewRequest(http.MethodGet, server.ClientConfig.Host+tc.path, nil)
 			if err != nil {
 				t.Fatal(err)
 			}

test/integration/etcd/data.go

@@ -294,16 +294,18 @@ func GetEtcdStorageDataForNamespaceServedAt(namespace string, v string, removeAl
 			IntroducedVersion: "1.7",
 		},
 		gvr("networking.k8s.io", "v1", "ipaddresses"): {
-			Stub:              `{"metadata": {"name": "192.168.2.3"}, "spec": {"parentRef": {"resource": "services","name": "test", "namespace": "ns"}}}`,
+			Stub:                                   `{"metadata": {"name": "192.168.2.3"}, "spec": {"parentRef": {"resource": "services","name": "test", "namespace": "ns"}}}`,
-			ExpectedEtcdPath:  "/registry/ipaddresses/192.168.2.3",
+			ExpectedEtcdPath:                       "/registry/ipaddresses/192.168.2.3",
-			ExpectedGVK:       gvkP("networking.k8s.io", "v1beta1", "IPAddress"),
+			ExpectedGVK:                            gvkP("networking.k8s.io", "v1beta1", "IPAddress"),
-			IntroducedVersion: "1.33",
+			IntroducedVersion:                      "1.33",
+			EmulationForwardCompatibleSinceVersion: "1.31",
 		},
 		gvr("networking.k8s.io", "v1", "servicecidrs"): {
-			Stub:              `{"metadata": {"name": "range-b2"}, "spec": {"cidrs": ["192.168.0.0/16","fd00:1::/120"]}}`,
+			Stub:                                   `{"metadata": {"name": "range-b2"}, "spec": {"cidrs": ["192.168.0.0/16","fd00:1::/120"]}}`,
-			ExpectedEtcdPath:  "/registry/servicecidrs/range-b2",
+			ExpectedEtcdPath:                       "/registry/servicecidrs/range-b2",
-			ExpectedGVK:       gvkP("networking.k8s.io", "v1beta1", "ServiceCIDR"),
+			ExpectedGVK:                            gvkP("networking.k8s.io", "v1beta1", "ServiceCIDR"),
-			IntroducedVersion: "1.33",
+			IntroducedVersion:                      "1.33",
+			EmulationForwardCompatibleSinceVersion: "1.31",
 		},
 		// --
 
@@ -643,13 +645,16 @@ func GetEtcdStorageDataForNamespaceServedAt(namespace string, v string, removeAl
 
 	// Delete types no longer served or not yet added at a particular emulated version.
 	for key, data := range etcdStorageData {
-		if data.IntroducedVersion != "" && version.MustParse(data.IntroducedVersion).GreaterThan(version.MustParse(v)) {
-			delete(etcdStorageData, key)
-		}
-
 		if data.RemovedVersion != "" && version.MustParse(v).AtLeast(version.MustParse(data.RemovedVersion)) {
 			delete(etcdStorageData, key)
 		}
+		if data.IntroducedVersion == "" || version.MustParse(v).AtLeast(version.MustParse(data.IntroducedVersion)) {
+			continue
+		}
+		if data.EmulationForwardCompatibleSinceVersion != "" && version.MustParse(v).AtLeast(version.MustParse(data.EmulationForwardCompatibleSinceVersion)) {
+			continue
+		}
+		delete(etcdStorageData, key)
 	}
 
 	if removeAlphas {
@@ -693,6 +698,10 @@ type StorageData struct {
 	ExpectedGVK       *schema.GroupVersionKind // The GVK that we expect this object to be stored as - leave this nil to use the default
 	IntroducedVersion string                   // The version that this type is introduced
 	RemovedVersion    string                   // The version that this type is removed. May be empty for stable resources
+	// EmulationForwardCompatibleSinceVersion indicates the api should be kept if the emulation version is >= this version, even when the api is introduced after the emulation version.
+	// Only needed for some Beta (Beta2+) and GA APIs, and is the version when the lowest Beta api is introduced.
+	// This is needed to enable some Beta features where the api used in the corresponding controller has GAed.
+	EmulationForwardCompatibleSinceVersion string
 }
 
 // Prerequisite contains information required to create a resource (but not verify it)

test/integration/etcd/etcd_storage_path_test.go

@@ -45,7 +45,6 @@ import (
 	featuregatetesting "k8s.io/component-base/featuregate/testing"
 	componentbaseversion "k8s.io/component-base/version"
 	"k8s.io/kubernetes/cmd/kube-apiserver/app/options"
-	"k8s.io/kubernetes/pkg/features"
 )
 
 // Only add kinds to this list when this a virtual resource with get and create verbs that doesn't actually
@@ -95,19 +94,12 @@ func testEtcdStoragePathWithVersion(t *testing.T, v string) {
 		// Only test for beta and GA APIs with emulated version.
 		featuregatetesting.SetFeatureGateEmulationVersionDuringTest(t, feature.DefaultFeatureGate, version.MustParse(v))
 		featuregatetesting.SetFeatureGateDuringTest(t, feature.DefaultFeatureGate, "AllBeta", true)
-		// Feature Gates that are GA and depend directly on the API version to work can not be emulated in previous versions.
-		// Example feature:
-		// v1.x-2 : FeatureGate alpha , API v1alpha1/feature
-		// v1.x-1 : FeatureGate beta  , API v1beta1/feature
-		// v1.x   : FeatureGate GA    , API v1/feature
-		// The code in v1.x uses the clients with the v1 API, if we emulate v1.x-1 it will not work against apiserver that
-		// only understand v1beta1.
-		featuregatetesting.SetFeatureGateDuringTest(t, feature.DefaultFeatureGate, features.MultiCIDRServiceAllocator, false)
 	}
 
 	apiServer := StartRealAPIServerOrDie(t, func(opts *options.ServerRunOptions) {
 		// Disable alphas when emulating previous versions.
 		if v != componentbaseversion.DefaultKubeBinaryVersion {
+			opts.Options.GenericServerRunOptions.EmulationForwardCompatible = true
 			opts.Options.APIEnablement.RuntimeConfig["api/alpha"] = "false"
 		}
 	})