discovery/aggregated: Add invalidation callback support

Add callback mechanism to notify peer-aggregated discovery handler when local discovery changes, enabling efficient cache invalidation. Part of KEP-4020: Unknown Version Interoperability Proxy Kubernetes-commit: c72f9f73d92ff5e7a28f06c110acbc9626e4252d

Author: richabanker

pkg/endpoints/discovery/aggregated/handler.go

@@ -85,6 +85,9 @@ type ResourceManager interface {
 // The group from the least-numbered source is used
 WithSource(source Source) ResourceManager
 
+// AddInvalidationCallback adds a callback to be called when the discovery cache is invalidated.
+AddInvalidationCallback(callback func())
+
 http.Handler
 }
 
@@ -116,6 +119,10 @@ func (rm resourceManager) WithSource(source Source) ResourceManager {
 }
 }
 
+func (rm resourceManager) AddInvalidationCallback(callback func()) {
+rm.resourceDiscoveryManager.AddInvalidationCallback(callback)
+}
+
 type groupKey struct {
 name string
 
@@ -138,16 +145,28 @@ type resourceDiscoveryManager struct {
 
 // Writes protected by the lock.
 // List of all apigroups & resources indexed by the resource manager
-lock sync.RWMutex
-apiGroups map[groupKey]*apidiscoveryv2.APIGroupDiscovery
-versionPriorities map[groupVersionKey]priorityInfo
+lock sync.RWMutex
+apiGroups map[groupKey]*apidiscoveryv2.APIGroupDiscovery
+versionPriorities map[groupVersionKey]priorityInfo
+invalidationCallback atomic.Pointer[func()]
 }
 
 type priorityInfo struct {
 GroupPriorityMinimum int
 VersionPriority int
 }
 
+func (rdm *resourceDiscoveryManager) AddInvalidationCallback(callback func()) {
+rdm.invalidationCallback.Store(&callback)
+}
+
+func (rdm *resourceDiscoveryManager) invalidateCacheLocked() {
+rdm.cache.Store(nil)
+if callback := rdm.invalidationCallback.Load(); callback != nil {
+(*callback)()
+}
+}
+
 func NewResourceManager(path string) ResourceManager {
 scheme := runtime.NewScheme()
 utilruntime.Must(apidiscoveryv2.AddToScheme(scheme))
@@ -188,15 +207,15 @@ func (rdm *resourceDiscoveryManager) SetGroupVersionPriority(source Source, gv m
 GroupPriorityMinimum: groupPriorityMinimum,
 VersionPriority: versionPriority,
 }
-rdm.cache.Store(nil)
+rdm.invalidateCacheLocked()
 }
 
 func (rdm *resourceDiscoveryManager) SetGroups(source Source, groups []apidiscoveryv2.APIGroupDiscovery) {
 rdm.lock.Lock()
 defer rdm.lock.Unlock()
 
 rdm.apiGroups = nil
-rdm.cache.Store(nil)
+rdm.invalidateCacheLocked()
 
 for _, group := range groups {
 for _, version := range group.Versions {
@@ -297,7 +316,7 @@ func (rdm *resourceDiscoveryManager) addGroupVersionLocked(source Source, groupN
 }
 
 // Reset response document so it is recreated lazily
-rdm.cache.Store(nil)
+rdm.invalidateCacheLocked()
 }
 
 func (rdm *resourceDiscoveryManager) RemoveGroupVersion(source Source, apiGroup metav1.GroupVersion) {
@@ -338,7 +357,7 @@ func (rdm *resourceDiscoveryManager) RemoveGroupVersion(source Source, apiGroup
 }
 
 // Reset response document so it is recreated lazily
-rdm.cache.Store(nil)
+rdm.invalidateCacheLocked()
 }
 
 func (rdm *resourceDiscoveryManager) RemoveGroup(source Source, groupName string) {
@@ -521,53 +540,62 @@ func (rdm *resourceDiscoveryManager) serveHTTP(resp http.ResponseWriter, req *ht
 response := cache.cachedResponse
 etag := cache.cachedResponseETag
 
-mediaType, _, err := negotiation.NegotiateOutputMediaType(req, rdm.serializer, DiscoveryEndpointRestrictions)
+writeDiscoveryResponse(&response, etag, rdm.serializer, resp, req)
+}
+
+func writeDiscoveryResponse(
+resp *apidiscoveryv2.APIGroupDiscoveryList,
+etag string,
+serializer runtime.NegotiatedSerializer,
+w http.ResponseWriter,
+req *http.Request,
+) {
+mediaType, _, err := negotiation.NegotiateOutputMediaType(req, serializer, DiscoveryEndpointRestrictions)
 if err != nil {
 // Should never happen. wrapper.go will only proxy requests to this
 // handler if the media type passes DiscoveryEndpointRestrictions
 utilruntime.HandleError(err)
-resp.WriteHeader(http.StatusInternalServerError)
+w.WriteHeader(http.StatusInternalServerError)
 return
 }
 var targetGV schema.GroupVersion
 if mediaType.Convert == nil ||
 (mediaType.Convert.GroupVersion() != apidiscoveryv2.SchemeGroupVersion &&
 mediaType.Convert.GroupVersion() != apidiscoveryv2beta1.SchemeGroupVersion) {
 utilruntime.HandleError(fmt.Errorf("expected aggregated discovery group version, got group: %s, version %s", mediaType.Convert.Group, mediaType.Convert.Version))
-resp.WriteHeader(http.StatusInternalServerError)
+w.WriteHeader(http.StatusInternalServerError)
 return
 }
 
 if mediaType.Convert.GroupVersion() == apidiscoveryv2beta1.SchemeGroupVersion &&
 utilfeature.DefaultFeatureGate.Enabled(genericfeatures.AggregatedDiscoveryRemoveBetaType) {
 klog.Errorf("aggregated discovery version v2beta1 is removed. Please update to use v2")
-resp.WriteHeader(http.StatusNotFound)
+w.WriteHeader(http.StatusNotFound)
 return
 }
-
 targetGV = mediaType.Convert.GroupVersion()
 
 if len(etag) > 0 {
 // Use proper e-tag headers if one is available
 ServeHTTPWithETag(
-&response,
+resp,
 etag,
 targetGV,
-rdm.serializer,
-resp,
+serializer,
+w,
 req,
 )
 } else {
 // Default to normal response in rare case etag is
 // not cached with the object for some reason.
 responsewriters.WriteObjectNegotiated(
-rdm.serializer,
+serializer,
 DiscoveryEndpointRestrictions,
 targetGV,
-resp,
+w,
 req,
 http.StatusOK,
-&response,
+resp,
 true,
 )
 }