webhook: cache miss fallback to direct client for ScaledObject

Signed-off-by: Jan Wozniak <wozniak.jan@gmail.com>

CHANGELOG.md

@@ -60,6 +60,7 @@ To learn more about active deprecations, we recommend checking [GitHub Discussio
 - **CloudEventSource**: Introduce ClusterCloudEventSource ([#3533](https://github.com/kedacore/keda/issues/3533))
 - **CloudEventSource**: Provide ClusterCloudEventSource around the management of ScaledJobs resources ([#3523](https://github.com/kedacore/keda/issues/3523))
 - **CloudEventSource**: Provide ClusterCloudEventSource around the management of TriggerAuthentication/ClusterTriggerAuthentication resources ([#3524](https://github.com/kedacore/keda/issues/3524))
+- **General**: Cache miss fallback in validating webhook for ScaledObjects with direct kubernetes client ([#5973](https://github.com/kedacore/keda/issues/5973))
 
 #### Experimental
 

apis/keda/v1alpha1/scaledobject_webhook.go

@@ -29,6 +29,7 @@ import (
 	appsv1 "k8s.io/api/apps/v1"
 	autoscalingv2 "k8s.io/api/autoscaling/v2"
 	corev1 "k8s.io/api/core/v1"
+	kerrors "k8s.io/apimachinery/pkg/api/errors"
 	"k8s.io/apimachinery/pkg/api/meta"
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/types"
@@ -44,14 +45,31 @@ import (
 var scaledobjectlog = logf.Log.WithName("scaledobject-validation-webhook")
 
 var kc client.Client
+var cacheMissToDirectClient bool
+var directClient client.Client
 var restMapper meta.RESTMapper
 
 var memoryString = "memory"
 var cpuString = "cpu"
 
-func (so *ScaledObject) SetupWebhookWithManager(mgr ctrl.Manager) error {
+func (so *ScaledObject) SetupWebhookWithManager(mgr ctrl.Manager, cacheMissFallback bool) error {
 	kc = mgr.GetClient()
 	restMapper = mgr.GetRESTMapper()
+	cacheMissToDirectClient = cacheMissFallback
+	if cacheMissToDirectClient {
+		cfg := mgr.GetConfig()
+		opts := client.Options{
+			HTTPClient: mgr.GetHTTPClient(),
+			Scheme:     mgr.GetScheme(),
+			Mapper:     restMapper,
+			Cache:      nil, // this disables the cache and explicitly uses the direct client
+		}
+		var err error
+		directClient, err = client.New(cfg, opts)
+		if err != nil {
+			return fmt.Errorf("failed to initialize direct client: %v", err)
+		}
+	}
 	return ctrl.NewWebhookManagedBy(mgr).
 		WithValidator(&ScaledObjectCustomValidator{}).
 		For(so).
@@ -312,6 +330,18 @@ func verifyScaledObjects(incomingSo *ScaledObject, action string, _ bool) error
 	return nil
 }
 
+// getFromCacheOrDirect is a helper function that tries to get an object from the cache
+// if it fails, it tries to get it from the direct client
+func getFromCacheOrDirect(ctx context.Context, key client.ObjectKey, obj client.Object) error {
+	err := kc.Get(ctx, key, obj, &client.GetOptions{})
+	if cacheMissToDirectClient {
+		if kerrors.IsNotFound(err) {
+			return directClient.Get(ctx, key, obj, &client.GetOptions{})
+		}
+	}
+	return err
+}
+
 func verifyCPUMemoryScalers(incomingSo *ScaledObject, action string, dryRun bool) error {
 	if dryRun {
 		return nil
@@ -334,15 +364,13 @@ func verifyCPUMemoryScalers(incomingSo *ScaledObject, action string, dryRun bool
 				switch incomingSoGckr.GVKString() {
 				case "apps/v1.Deployment":
 					deployment := &appsv1.Deployment{}
-					err := kc.Get(context.Background(), key, deployment, &client.GetOptions{})
-					if err != nil {
+					if err := getFromCacheOrDirect(context.Background(), key, deployment); err != nil {
 						return err
 					}
 					podSpec = &deployment.Spec.Template.Spec
 				case "apps/v1.StatefulSet":
 					statefulset := &appsv1.StatefulSet{}
-					err := kc.Get(context.Background(), key, statefulset, &client.GetOptions{})
-					if err != nil {
+					if err := getFromCacheOrDirect(context.Background(), key, statefulset); err != nil {
 						return err
 					}
 					podSpec = &statefulset.Spec.Template.Spec

apis/keda/v1alpha1/suite_test.go

@@ -118,7 +118,7 @@ var _ = BeforeSuite(func() {
 	})
 	Expect(err).NotTo(HaveOccurred())
 
-	err = (&ScaledObject{}).SetupWebhookWithManager(mgr)
+	err = (&ScaledObject{}).SetupWebhookWithManager(mgr, false)
 	Expect(err).NotTo(HaveOccurred())
 	err = (&ScaledJob{}).SetupWebhookWithManager(mgr)
 	Expect(err).NotTo(HaveOccurred())

cmd/webhooks/main.go

@@ -62,6 +62,7 @@ func main() {
 	var webhooksClientRequestBurst int
 	var certDir string
 	var webhooksPort int
+	var cacheMissToDirectClient bool
 
 	pflag.StringVar(&metricsAddr, "metrics-bind-address", ":8080", "The address the metric endpoint binds to.")
 	pflag.StringVar(&probeAddr, "health-probe-bind-address", ":8081", "The address the probe endpoint binds to.")
@@ -70,6 +71,7 @@ func main() {
 	pflag.IntVar(&webhooksClientRequestBurst, "kube-api-burst", 30, "Set the burst for throttling requests sent to the apiserver")
 	pflag.StringVar(&certDir, "cert-dir", "/certs", "Webhook certificates dir to use. Defaults to /certs")
 	pflag.IntVar(&webhooksPort, "port", 9443, "Port number to serve webhooks. Defaults to 9443")
+	pflag.BoolVar(&cacheMissToDirectClient, "cache-miss-to-direct-client", false, "If true, on cache misses the webhook will call the direct client to fetch the object")
 
 	opts := zap.Options{}
 	opts.BindFlags(flag.CommandLine)
@@ -117,7 +119,7 @@ func main() {
 
 	kedautil.PrintWelcome(setupLog, kubeVersion, "admission webhooks")
 
-	setupWebhook(mgr)
+	setupWebhook(mgr, cacheMissToDirectClient)
 
 	if err := mgr.AddHealthzCheck("healthz", healthz.Ping); err != nil {
 		setupLog.Error(err, "unable to set up health check")
@@ -134,9 +136,9 @@ func main() {
 	}
 }
 
-func setupWebhook(mgr manager.Manager) {
+func setupWebhook(mgr manager.Manager, cacheMissToDirectClient bool) {
 	// setup webhooks
-	if err := (&kedav1alpha1.ScaledObject{}).SetupWebhookWithManager(mgr); err != nil {
+	if err := (&kedav1alpha1.ScaledObject{}).SetupWebhookWithManager(mgr, cacheMissToDirectClient); err != nil {
 		setupLog.Error(err, "unable to create webhook", "webhook", "ScaledObject")
 		os.Exit(1)
 	}