Add ability to skip OpenAPI handler installation

cmd/kube-apiserver/app/aggregator.go

@@ -67,6 +67,9 @@ func createAggregatorConfig(
 	genericConfig := kubeAPIServerConfig
 	genericConfig.PostStartHooks = map[string]genericapiserver.PostStartHookConfigEntry{}
 	genericConfig.RESTOptionsGetter = nil
+	// prevent generic API server from installing the OpenAPI handler. Aggregator server
+	// has its own customized OpenAPI handler.
+	genericConfig.SkipOpenAPIInstallation = true
 
 	if utilfeature.DefaultFeatureGate.Enabled(genericfeatures.StorageVersionAPI) &&
 		utilfeature.DefaultFeatureGate.Enabled(genericfeatures.APIServerIdentity) {

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

@@ -165,6 +165,8 @@ type Config struct {
 	Serializer runtime.NegotiatedSerializer
 	// OpenAPIConfig will be used in generating OpenAPI spec. This is nil by default. Use DefaultOpenAPIConfig for "working" defaults.
 	OpenAPIConfig *openapicommon.Config
+	// SkipOpenAPIInstallation avoids installing the OpenAPI handler if set to true.
+	SkipOpenAPIInstallation bool
 
 	// RESTOptionsGetter is used to construct RESTStorage types via the generic registry.
 	RESTOptionsGetter genericregistry.RESTOptionsGetter
@@ -571,7 +573,8 @@ func (c completedConfig) New(name string, delegationTarget DelegationTarget) (*G
 
 		listedPathProvider: apiServerHandler,
 
-		openAPIConfig: c.OpenAPIConfig,
+		openAPIConfig:           c.OpenAPIConfig,
+		skipOpenAPIInstallation: c.SkipOpenAPIInstallation,
 
 		postStartHooks:         map[string]postStartHookEntry{},
 		preShutdownHooks:       map[string]preShutdownHookEntry{},

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

@@ -133,8 +133,14 @@ type GenericAPIServer struct {
 	// Enable swagger and/or OpenAPI if these configs are non-nil.
 	openAPIConfig *openapicommon.Config
 
+	// SkipOpenAPIInstallation indicates not to install the OpenAPI handler
+	// during PrepareRun.
+	// Set this to true when the specific API Server has its own OpenAPI handler
+	// (e.g. kube-aggregator)
+	skipOpenAPIInstallation bool
+
 	// OpenAPIVersionedService controls the /openapi/v2 endpoint, and can be used to update the served spec.
-	// It is set during PrepareRun.
+	// It is set during PrepareRun if `openAPIConfig` is non-nil unless `skipOpenAPIInstallation` is true.
 	OpenAPIVersionedService *handler.OpenAPIService
 
 	// StaticOpenAPISpec is the spec derived from the restful container endpoints.
@@ -289,7 +295,7 @@ type preparedGenericAPIServer struct {
 func (s *GenericAPIServer) PrepareRun() preparedGenericAPIServer {
 	s.delegationTarget.PrepareRun()
 
-	if s.openAPIConfig != nil {
+	if s.openAPIConfig != nil && !s.skipOpenAPIInstallation {
 		s.OpenAPIVersionedService, s.StaticOpenAPISpec = routes.OpenAPI{
 			Config: s.openAPIConfig,
 		}.Install(s.Handler.GoRestfulContainer, s.Handler.NonGoRestfulMux)

staging/src/k8s.io/kube-aggregator/pkg/cmd/server/start.go

@@ -142,6 +142,9 @@ func (o AggregatorOptions) RunAggregator(stopCh <-chan struct{}) error {
 	)
 	serverConfig.OpenAPIConfig = genericapiserver.DefaultOpenAPIConfig(openapi.GetOpenAPIDefinitions, openapinamer.NewDefinitionNamer(aggregatorscheme.Scheme))
 	serverConfig.OpenAPIConfig.Info.Title = "kube-aggregator"
+	// prevent generic API server from installing the OpenAPI handler. Aggregator server
+	// has its own customized OpenAPI handler.
+	serverConfig.SkipOpenAPIInstallation = true
 
 	serviceResolver := apiserver.NewClusterIPServiceResolver(serverConfig.SharedInformerFactory.Core().V1().Services().Lister())