For scaling deployments in particular, use a direct object get rather than the /scale API (#1458)

* For scaling deployments in particular, use a direct object get rather than the /scale API so that it can use the informer cache for better performance.

This is annoying as a special case but is so common and improves performance so much that I think it's worthwhile to include. Another option would be to majorly increase the QPS rate limit on the scaling API client however that would also increase kube-apiserver load while watches/informers are generally much less impactful.

Signed-off-by: Noah Kantrowitz <noah@coderanger.net>

* Update changelog.

Signed-off-by: Noah Kantrowitz <noah@coderanger.net>

* Use the already-normalized GVKR data so less weird string parsing.

Also adds support for StatefulSets for symmetry.

Signed-off-by: Noah Kantrowitz <noah@coderanger.net>

* Apply suggestions from code review

Co-authored-by: Zbynek Roubalik <726523+zroubalik@users.noreply.github.com>

Signed-off-by: Noah Kantrowitz <noah@coderanger.net>

* Apply suggestions from code review

Co-authored-by: Zbynek Roubalik <726523+zroubalik@users.noreply.github.com>

Signed-off-by: Noah Kantrowitz <noah@coderanger.net>

Author: coderanger

CHANGELOG.md

@@ -34,6 +34,7 @@
 - Add support for the WATCH_NAMESPACE environment variable to the operator ([#1474](https://github.com/kedacore/keda/pull/1474))
 - Automatically determine the RabbitMQ protocol when possible, and support setting the protocl via TriggerAuthentication ([#1459](https://github.com/kedacore/keda/pulls/1459),[#1483](https://github.com/kedacore/keda/pull/1483))
 - Improve performance when fetching pod information ([#1457](https://github.com/kedacore/keda/pull/1457))
+- Improve performance when fetching current scaling information on Deployments ([#1458](https://github.com/kedacore/keda/pull/1458))
 
 ### Breaking Changes
 

controllers/scaledobject_controller.go

@@ -69,6 +69,7 @@ func init() {
 // SetupWithManager initializes the ScaledObjectReconciler instance and starts a new controller managed by the passed Manager instance.
 func (r *ScaledObjectReconciler) SetupWithManager(mgr ctrl.Manager) error {
 	// create Discovery clientset
+	// TODO If we need to increase the QPS of scaling API calls, copy and tweak this RESTConfig.
 	clientset, err := discovery.NewDiscoveryClientForConfig(mgr.GetConfig())
 	if err != nil {
 		r.Log.Error(err, "Not able to create Discovery clientset")

pkg/scaling/executor/scale_scaledobjects.go

@@ -5,8 +5,10 @@ import (
 	"time"
 
 	"github.com/go-logr/logr"
+	appsv1 "k8s.io/api/apps/v1"
 	autoscalingv1 "k8s.io/api/autoscaling/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"sigs.k8s.io/controller-runtime/pkg/client"
 
 	kedav1alpha1 "github.com/kedacore/keda/v2/api/v1alpha1"
 )
@@ -16,18 +18,46 @@ func (e *scaleExecutor) RequestScale(ctx context.Context, scaledObject *kedav1al
 		"scaledObject.Namespace", scaledObject.Namespace,
 		"scaleTarget.Name", scaledObject.Spec.ScaleTargetRef.Name)
 
-	currentScale, err := e.getScaleTargetScale(ctx, scaledObject)
-	if err != nil {
-		logger.Error(err, "Error getting information on the current Scale (ie. replias count) on the scaleTarget")
-		return
+	// Get the current replica count. As a special case, Deployments and StatefulSets fetch directly from the object so they can use the informer cache
+	// to reduce API calls. Everything else uses the scale subresource.
+	var currentScale *autoscalingv1.Scale
+	var currentReplicas int32
+	targetName := scaledObject.Spec.ScaleTargetRef.Name
+	targetGVKR := scaledObject.Status.ScaleTargetGVKR
+	switch {
+	case targetGVKR.Group == "apps" && targetGVKR.Kind == "Deployment":
+		deployment := &appsv1.Deployment{}
+		err := e.client.Get(ctx, client.ObjectKey{Name: targetName, Namespace: scaledObject.Namespace}, deployment)
+		if err != nil {
+			logger.Error(err, "Error getting information on the current Scale (ie. replicas count) on the scaleTarget")
+			return
+		}
+		currentReplicas = *deployment.Spec.Replicas
+	case targetGVKR.Group == "apps" && targetGVKR.Kind == "StatefulSet":
+		statefulSet := &appsv1.StatefulSet{}
+		err := e.client.Get(ctx, client.ObjectKey{Name: targetName, Namespace: scaledObject.Namespace}, statefulSet)
+		if err != nil {
+			logger.Error(err, "Error getting information on the current Scale (ie. replicas count) on the scaleTarget")
+			return
+		}
+		currentReplicas = *statefulSet.Spec.Replicas
+	default:
+		var err error
+		currentScale, err = e.getScaleTargetScale(ctx, scaledObject)
+		if err != nil {
+			logger.Error(err, "Error getting information on the current Scale (ie. replicas count) on the scaleTarget")
+			return
+		}
+		currentReplicas = currentScale.Spec.Replicas
 	}
+
 	switch {
-	case currentScale.Spec.Replicas == 0 && isActive:
+	case currentReplicas == 0 && isActive:
 		// current replica count is 0, but there is an active trigger.
 		// scale the ScaleTarget up
 		e.scaleFromZero(ctx, logger, scaledObject, currentScale)
 	case !isActive &&
-		currentScale.Spec.Replicas > 0 &&
+		currentReplicas > 0 &&
 		(scaledObject.Spec.MinReplicaCount == nil || *scaledObject.Spec.MinReplicaCount == 0):
 		// there are no active triggers, but the ScaleTarget has replicas.
 		// AND
@@ -37,14 +67,12 @@ func (e *scaleExecutor) RequestScale(ctx context.Context, scaledObject *kedav1al
 		e.scaleToZero(ctx, logger, scaledObject, currentScale)
 	case !isActive &&
 		scaledObject.Spec.MinReplicaCount != nil &&
-		currentScale.Spec.Replicas < *scaledObject.Spec.MinReplicaCount:
+		currentReplicas < *scaledObject.Spec.MinReplicaCount:
 		// there are no active triggers
 		// AND
 		// ScaleTarget replicas count is less than minimum replica count specified in ScaledObject
 		// Let's set ScaleTarget replicas count to correct value
-		currentScale.Spec.Replicas = *scaledObject.Spec.MinReplicaCount
-
-		err := e.updateScaleOnScaleTarget(ctx, scaledObject, currentScale)
+		_, err := e.updateScaleOnScaleTarget(ctx, scaledObject, currentScale, *scaledObject.Spec.MinReplicaCount)
 		if err == nil {
 			logger.Info("Successfully set ScaleTarget replicas count to ScaledObject minReplicaCount",
 				"ScaleTarget.Replicas", currentScale.Spec.Replicas)
@@ -93,8 +121,7 @@ func (e *scaleExecutor) scaleToZero(ctx context.Context, logger logr.Logger, sca
 	if scaledObject.Status.LastActiveTime == nil ||
 		scaledObject.Status.LastActiveTime.Add(cooldownPeriod).Before(time.Now()) {
 		// or last time a trigger was active was > cooldown period, so scale down.
-		scale.Spec.Replicas = 0
-		err := e.updateScaleOnScaleTarget(ctx, scaledObject, scale)
+		_, err := e.updateScaleOnScaleTarget(ctx, scaledObject, scale, 0)
 		if err == nil {
 			logger.Info("Successfully scaled ScaleTarget to 0 replicas")
 			if err := e.setActiveCondition(ctx, logger, scaledObject, metav1.ConditionFalse, "ScalerNotActive", "Scaling is not performed because triggers are not active"); err != nil {
@@ -118,19 +145,19 @@ func (e *scaleExecutor) scaleToZero(ctx context.Context, logger logr.Logger, sca
 }
 
 func (e *scaleExecutor) scaleFromZero(ctx context.Context, logger logr.Logger, scaledObject *kedav1alpha1.ScaledObject, scale *autoscalingv1.Scale) {
-	currentReplicas := scale.Spec.Replicas
+	var replicas int32
 	if scaledObject.Spec.MinReplicaCount != nil && *scaledObject.Spec.MinReplicaCount > 0 {
-		scale.Spec.Replicas = *scaledObject.Spec.MinReplicaCount
+		replicas = *scaledObject.Spec.MinReplicaCount
 	} else {
-		scale.Spec.Replicas = 1
+		replicas = 1
 	}
 
-	err := e.updateScaleOnScaleTarget(ctx, scaledObject, scale)
+	currentReplicas, err := e.updateScaleOnScaleTarget(ctx, scaledObject, scale, replicas)
 
 	if err == nil {
 		logger.Info("Successfully updated ScaleTarget",
 			"Original Replicas Count", currentReplicas,
-			"New Replicas Count", scale.Spec.Replicas)
+			"New Replicas Count", replicas)
 
 		// Scale was successful. Update lastScaleTime and lastActiveTime on the scaledObject
 		if err := e.updateLastActiveTime(ctx, logger, scaledObject); err != nil {
@@ -144,7 +171,20 @@ func (e *scaleExecutor) getScaleTargetScale(ctx context.Context, scaledObject *k
 	return (*e.scaleClient).Scales(scaledObject.Namespace).Get(ctx, scaledObject.Status.ScaleTargetGVKR.GroupResource(), scaledObject.Spec.ScaleTargetRef.Name, metav1.GetOptions{})
 }
 
-func (e *scaleExecutor) updateScaleOnScaleTarget(ctx context.Context, scaledObject *kedav1alpha1.ScaledObject, scale *autoscalingv1.Scale) error {
+func (e *scaleExecutor) updateScaleOnScaleTarget(ctx context.Context, scaledObject *kedav1alpha1.ScaledObject, scale *autoscalingv1.Scale, replicas int32) (int32, error) {
+	if scale == nil {
+		// Wasn't retrieved earlier, grab it now.
+		var err error
+		scale, err = e.getScaleTargetScale(ctx, scaledObject)
+		if err != nil {
+			return -1, err
+		}
+	}
+
+	// Update with requested repliacs.
+	currentReplicas := scale.Spec.Replicas
+	scale.Spec.Replicas = replicas
+
 	_, err := (*e.scaleClient).Scales(scaledObject.Namespace).Update(ctx, scaledObject.Status.ScaleTargetGVKR.GroupResource(), scale, metav1.UpdateOptions{})
-	return err
+	return currentReplicas, err
 }