Cache DiscoveryVariables calls

internal/controllers/clusterclass/clusterclass_controller.go

@@ -46,7 +46,9 @@ import (
 	runtimehooksv1 "sigs.k8s.io/cluster-api/exp/runtime/hooks/api/v1alpha1"
 	"sigs.k8s.io/cluster-api/feature"
 	runtimeclient "sigs.k8s.io/cluster-api/internal/runtime/client"
+	runtimeregistry "sigs.k8s.io/cluster-api/internal/runtime/registry"
 	"sigs.k8s.io/cluster-api/internal/topology/variables"
+	"sigs.k8s.io/cluster-api/internal/util/cache"
 	"sigs.k8s.io/cluster-api/util"
 	"sigs.k8s.io/cluster-api/util/conversion"
 	"sigs.k8s.io/cluster-api/util/patch"
@@ -67,6 +69,10 @@ type Reconciler struct {
 
 	// RuntimeClient is a client for calling runtime extensions.
 	RuntimeClient runtimeclient.Client
+
+	// discoverVariablesCache is used to temporarily store the response of a DiscoveryVariables call for
+	// a specific runtime extension/settings combination.
+	discoverVariablesCache cache.Cache[runtimeclient.CallExtensionCacheEntry]
 }
 
 func (r *Reconciler) SetupWithManager(ctx context.Context, mgr ctrl.Manager, options controller.Options) error {
@@ -91,6 +97,8 @@ func (r *Reconciler) SetupWithManager(ctx context.Context, mgr ctrl.Manager, opt
 	if err != nil {
 		return errors.Wrap(err, "failed setting up with a controller manager")
 	}
+
+	r.discoverVariablesCache = cache.New[runtimeclient.CallExtensionCacheEntry]()
 	return nil
 }
 
@@ -302,8 +310,13 @@ func (r *Reconciler) reconcileVariables(ctx context.Context, s *scope) (ctrl.Res
 			req := &runtimehooksv1.DiscoverVariablesRequest{}
 			req.Settings = patch.External.Settings
 
+			// We temporarily cache the response of a DiscoveryVariables call to improve performance in case there are
+			// many ClusterClasses using the same runtime extension/settings combination.
+			// This also mitigates spikes when ClusterClass re-syncs happen or when changes to the ExtensionConfig are applied.
+			// DiscoverVariables is expected to return a "static" response and usually there are few ExtensionConfigs in a mgmt cluster.
 			resp := &runtimehooksv1.DiscoverVariablesResponse{}
-			err := r.RuntimeClient.CallExtension(ctx, runtimehooksv1.DiscoverVariables, clusterClass, *patch.External.DiscoverVariablesExtension, req, resp)
+			err := r.RuntimeClient.CallExtension(ctx, runtimehooksv1.DiscoverVariables, clusterClass, *patch.External.DiscoverVariablesExtension, req, resp,
+				runtimeclient.WithCaching{Cache: r.discoverVariablesCache, CacheKeyFunc: cacheKeyFunc})
 			if err != nil {
 				errs = append(errs, errors.Wrapf(err, "failed to call DiscoverVariables for patch %s", patch.Name))
 				continue
@@ -492,3 +505,12 @@ func matchNamespace(ctx context.Context, c client.Client, selector labels.Select
 	}
 	return selector.Matches(labels.Set(ns.GetLabels()))
 }
+
+func cacheKeyFunc(registration *runtimeregistry.ExtensionRegistration, request runtimehooksv1.RequestObject) string {
+	// Note: registration.Name is identical to the value of the patch.External.DiscoverVariablesExtension field in the ClusterClass.
+	s := fmt.Sprintf("%s-%s", registration.Name, registration.ExtensionConfigResourceVersion)
+	for k, v := range request.GetSettings() {
+		s += fmt.Sprintf(",%s=%s", k, v)
+	}
+	return s
+}

internal/controllers/clusterclass/clusterclass_controller_test.go

@@ -43,7 +43,9 @@ import (
 	runtimecatalog "sigs.k8s.io/cluster-api/exp/runtime/catalog"
 	runtimehooksv1 "sigs.k8s.io/cluster-api/exp/runtime/hooks/api/v1alpha1"
 	"sigs.k8s.io/cluster-api/feature"
+	runtimeclient "sigs.k8s.io/cluster-api/internal/runtime/client"
 	fakeruntimeclient "sigs.k8s.io/cluster-api/internal/runtime/client/fake"
+	"sigs.k8s.io/cluster-api/internal/util/cache"
 	"sigs.k8s.io/cluster-api/util/test/builder"
 )
 
@@ -1154,7 +1156,8 @@ func TestReconciler_reconcileVariables(t *testing.T) {
 				Build()
 
 			r := &Reconciler{
-				RuntimeClient: fakeRuntimeClient,
+				RuntimeClient:          fakeRuntimeClient,
+				discoverVariablesCache: cache.New[runtimeclient.CallExtensionCacheEntry](),
 			}
 
 			// Pin the compatibility version used in variable CEL validation to 1.29, so we don't have to continuously refactor

internal/controllers/topology/cluster/patches/external/external_patch_generator_test.go

@@ -129,7 +129,7 @@ func (f *fakeRuntimeClient) CallAllExtensions(_ context.Context, _ runtimecatalo
 	panic("implement me")
 }
 
-func (f *fakeRuntimeClient) CallExtension(_ context.Context, _ runtimecatalog.Hook, _ metav1.Object, _ string, request runtimehooksv1.RequestObject, _ runtimehooksv1.ResponseObject) error {
+func (f *fakeRuntimeClient) CallExtension(_ context.Context, _ runtimecatalog.Hook, _ metav1.Object, _ string, request runtimehooksv1.RequestObject, _ runtimehooksv1.ResponseObject, _ ...runtimeclient.CallExtensionOption) error {
 	// Keep a copy of the request object.
 	// We keep a copy because the request is modified after the call is made. So we keep a copy to perform assertions.
 	f.callExtensionRequest = request.DeepCopyObject().(runtimehooksv1.RequestObject)

internal/runtime/client/client.go

@@ -27,6 +27,7 @@ import (
 	"net/http"
 	"net/url"
 	"path"
+	"reflect"
 	"strconv"
 	"strings"
 	"time"
@@ -49,6 +50,7 @@ import (
 	runtimehooksv1 "sigs.k8s.io/cluster-api/exp/runtime/hooks/api/v1alpha1"
 	runtimemetrics "sigs.k8s.io/cluster-api/internal/runtime/metrics"
 	runtimeregistry "sigs.k8s.io/cluster-api/internal/runtime/registry"
+	"sigs.k8s.io/cluster-api/internal/util/cache"
 	"sigs.k8s.io/cluster-api/util"
 )
 
@@ -96,7 +98,7 @@ type Client interface {
 	CallAllExtensions(ctx context.Context, hook runtimecatalog.Hook, forObject metav1.Object, request runtimehooksv1.RequestObject, response runtimehooksv1.ResponseObject) error
 
 	// CallExtension calls the ExtensionHandler with the given name.
-	CallExtension(ctx context.Context, hook runtimecatalog.Hook, forObject metav1.Object, name string, request runtimehooksv1.RequestObject, response runtimehooksv1.ResponseObject) error
+	CallExtension(ctx context.Context, hook runtimecatalog.Hook, forObject metav1.Object, name string, request runtimehooksv1.RequestObject, response runtimehooksv1.ResponseObject, opts ...CallExtensionOption) error
 }
 
 var _ Client = &client{}
@@ -276,6 +278,44 @@ func aggregateSuccessfulResponses(aggregatedResponse runtimehooksv1.ResponseObje
 	aggregatedResponse.SetMessage(strings.Join(messages, ", "))
 }
 
+// CallExtensionOption is the interface for configuration that modifies CallExtensionOptions for a CallExtension call.
+type CallExtensionOption interface {
+	// ApplyToOptions applies this configuration to the given CallExtensionOptions.
+	ApplyToOptions(*CallExtensionOptions)
+}
+
+// CallExtensionCacheEntry is a cache entry for the cache that can be used with the CallExtension call via
+// the WithCaching option.
+type CallExtensionCacheEntry struct {
+	CacheKey string
+	Response runtimehooksv1.ResponseObject
+}
+
+// Key returns the cache key of a CallExtensionCacheEntry.
+func (c CallExtensionCacheEntry) Key() string {
+	return c.CacheKey
+}
+
+// WithCaching enables caching for the CallExtension call.
+type WithCaching struct {
+	Cache        cache.Cache[CallExtensionCacheEntry]
+	CacheKeyFunc func(*runtimeregistry.ExtensionRegistration, runtimehooksv1.RequestObject) string
+}
+
+// ApplyToOptions applies WithCaching to the given CallExtensionOptions.
+func (w WithCaching) ApplyToOptions(in *CallExtensionOptions) {
+	in.WithCaching = true
+	in.Cache = w.Cache
+	in.CacheKeyFunc = w.CacheKeyFunc
+}
+
+// CallExtensionOptions contains the options for the CallExtension call.
+type CallExtensionOptions struct {
+	WithCaching  bool
+	Cache        cache.Cache[CallExtensionCacheEntry]
+	CacheKeyFunc func(*runtimeregistry.ExtensionRegistration, runtimehooksv1.RequestObject) string
+}
+
 // CallExtension makes the call to the extension with the given name.
 // The response object passed will be updated with the response of the call.
 // An error is returned if the extension is not compatible with the hook.
@@ -288,7 +328,13 @@ func aggregateSuccessfulResponses(aggregatedResponse runtimehooksv1.ResponseObje
 // Nb. FailurePolicy does not affect the following kinds of errors:
 // - Internal errors. Examples: hooks is incompatible with ExtensionHandler, ExtensionHandler information is missing.
 // - Error when ExtensionHandler returns a response with `Status` set to `Failure`.
-func (c *client) CallExtension(ctx context.Context, hook runtimecatalog.Hook, forObject metav1.Object, name string, request runtimehooksv1.RequestObject, response runtimehooksv1.ResponseObject) error {
+func (c *client) CallExtension(ctx context.Context, hook runtimecatalog.Hook, forObject metav1.Object, name string, request runtimehooksv1.RequestObject, response runtimehooksv1.ResponseObject, opts ...CallExtensionOption) error {
+	// Calculate the options.
+	options := &CallExtensionOptions{}
+	for _, opt := range opts {
+		opt.ApplyToOptions(options)
+	}
+
 	log := ctrl.LoggerFrom(ctx).WithValues("extensionHandler", name, "hook", runtimecatalog.HookName(hook))
 	ctx = ctrl.LoggerInto(ctx, log)
 	hookGVH, err := c.catalog.GroupVersionHook(hook)
@@ -331,15 +377,31 @@ func (c *client) CallExtension(ctx context.Context, hook runtimecatalog.Hook, fo
 	// Prepare the request by merging the settings in the registration with the settings in the request.
 	request = cloneAndAddSettings(request, registration.Settings)
 
-	opts := &httpCallOptions{
+	var cacheKey string
+	if options.WithCaching {
+		// Return a cached response if response is cached.
+		cacheKey = options.CacheKeyFunc(registration, request)
+		if cacheEntry, ok := options.Cache.Has(cacheKey); ok {
+			// Set response to cacheEntry.Response.
+			outVal := reflect.ValueOf(response)
+			cacheVal := reflect.ValueOf(cacheEntry.Response)
+			if !cacheVal.Type().AssignableTo(outVal.Type()) {
+				return fmt.Errorf("failed to call extension handler %q: cached response of type %s instead of type %s", name, cacheVal.Type(), outVal.Type())
+			}
+			reflect.Indirect(outVal).Set(reflect.Indirect(cacheVal))
+			return nil
+		}
+	}
+
+	httpOpts := &httpCallOptions{
 		catalog:         c.catalog,
 		config:          registration.ClientConfig,
 		registrationGVH: registration.GroupVersionHook,
 		hookGVH:         hookGVH,
 		name:            strings.TrimSuffix(registration.Name, "."+registration.ExtensionConfigName),
 		timeout:         timeoutDuration,
 	}
-	err = httpCall(ctx, request, response, opts)
+	err = httpCall(ctx, request, response, httpOpts)
 	if err != nil {
 		// If the error is errCallingExtensionHandler then apply failure policy to calculate
 		// the effective result of the operation.
@@ -368,6 +430,14 @@ func (c *client) CallExtension(ctx context.Context, hook runtimecatalog.Hook, fo
 		log.V(4).Info("Extension handler returned success response")
 	}
 
+	if options.WithCaching {
+		// Add response to the cache.
+		options.Cache.Add(CallExtensionCacheEntry{
+			CacheKey: cacheKey,
+			Response: response,
+		})
+	}
+
 	// Received a successful response from the extension handler. The `response` object
 	// has been populated with the result. Return no error.
 	return nil