Fix KPA initial scale exceeding max scale

pkg/reconciler/autoscaling/kpa/kpa.go

@@ -324,9 +324,12 @@ func computeActiveCondition(ctx context.Context, pa *autoscalingv1alpha1.PodAuto
 // activeThreshold returns the scale required for the pa to be marked Active
 func activeThreshold(ctx context.Context, pa *autoscalingv1alpha1.PodAutoscaler) int {
 	asConfig := config.FromContext(ctx).Autoscaler
-	min, _ := pa.ScaleBounds(asConfig)
+	min, maxScale := pa.ScaleBounds(asConfig)
 	if !pa.Status.IsScaleTargetInitialized() {
 		initialScale := resources.GetInitialScale(asConfig, pa)
+		if maxScale > 0 && initialScale > maxScale {
+			initialScale = maxScale
+		}
 		return int(max(min, initialScale))
 	}
 	return int(max(min, 1))

pkg/reconciler/autoscaling/kpa/kpa_test.go

@@ -1060,6 +1060,59 @@ func TestReconcile(t *testing.T) {
 			Name:       deployName,
 			Patch:      fmt.Appendf(nil, `[{"op":"add","path":"/spec/replicas","value":%d}]`, 20),
 		}},
+	}, {
+		Name: "initial scale > maxScale, have not reached maxScale ready pods, PA still activating",
+		Key:  key,
+		Ctx: context.WithValue(context.Background(), deciderKey{},
+			decider(testNamespace, testRevision, defaultScale, /* desiredScale */
+				-42 /* ebc */)),
+		Objects: append([]runtime.Object{
+			kpa(testNamespace, testRevision, WithPASKSReady, WithBufferedTraffic,
+				withScales(1, 1), WithReachabilityReachable,
+				withInitialScale(20), withMaxScale(2), WithPAStatusService(testRevision), WithPAMetricsService(privateSvc)),
+			sks(testNamespace, testRevision, WithDeployRef(deployName), WithProxyMode, WithSKSReady, WithNumActivators(3)),
+			defaultMetric, defaultDeployment,
+		}, makeReadyPods(1, testNamespace, testRevision)...),
+		WantStatusUpdates: []clientgotesting.UpdateActionImpl{{
+			Object: kpa(testNamespace, testRevision, WithPASKSReady, WithBufferedTraffic,
+				withScales(1, 2), WithReachabilityReachable,
+				withInitialScale(20), withMaxScale(2), WithPAStatusService(testRevision), WithPAMetricsService(privateSvc),
+				WithObservedGeneration(1),
+			),
+		}},
+		WantPatches: []clientgotesting.PatchActionImpl{{
+			ActionImpl: clientgotesting.ActionImpl{Namespace: testNamespace},
+			Name:       deployName,
+			Patch:      fmt.Appendf(nil, `[{"op":"add","path":"/spec/replicas","value":%d}]`, 2),
+		}},
+	}, {
+		Name: "initial scale > maxScale, reaching maxScale ready pods marks PA as active",
+		Key:  key,
+		Ctx: context.WithValue(context.Background(), deciderKey{},
+			decider(testNamespace, testRevision, defaultScale, /* desiredScale */
+				-42 /* ebc */)),
+		Objects: append([]runtime.Object{
+			kpa(testNamespace, testRevision, WithPASKSReady, WithBufferedTraffic,
+				withScales(2, 2), withInitialScale(20), withMaxScale(2), WithReachabilityReachable,
+				WithPAStatusService(testRevision), WithPAMetricsService(privateSvc),
+			),
+			sks(testNamespace, testRevision, WithDeployRef(deployName), WithProxyMode, WithSKSReady, WithNumActivators(3)),
+			defaultMetric,
+			deploy(testNamespace, testRevision, func(d *appsv1.Deployment) {
+				d.Spec.Replicas = ptr.Int32(defaultScale)
+			}),
+		}, makeReadyPods(2, testNamespace, testRevision)...),
+		WantStatusUpdates: []clientgotesting.UpdateActionImpl{{
+			Object: kpa(testNamespace, testRevision, WithPASKSReady, WithTraffic,
+				markScaleTargetInitialized, withScales(2, 2), withInitialScale(20), withMaxScale(2), WithReachabilityReachable,
+				WithPAStatusService(testRevision), WithPAMetricsService(privateSvc), WithObservedGeneration(1),
+			),
+		}},
+		WantPatches: []clientgotesting.PatchActionImpl{{
+			ActionImpl: clientgotesting.ActionImpl{Namespace: testNamespace},
+			Name:       deployName,
+			Patch:      fmt.Appendf(nil, `[{"op":"add","path":"/spec/replicas","value":%d}]`, 2),
+		}},
 	}, {
 		Name: "initial scale zero: scale to zero",
 		Key:  key,
@@ -2012,6 +2065,15 @@ func withInitialScale(initScale int) PodAutoscalerOption {
 	}
 }
 
+func withMaxScale(maxScale int) PodAutoscalerOption {
+	return func(pa *autoscalingv1alpha1.PodAutoscaler) {
+		pa.Annotations = kmap.Union(
+			pa.Annotations,
+			map[string]string{autoscaling.MaxScaleAnnotationKey: strconv.Itoa(maxScale)},
+		)
+	}
+}
+
 func TestComputeActivatorNum(t *testing.T) {
 	cases := []struct {
 		name    string

pkg/reconciler/autoscaling/kpa/scaler.go

@@ -347,6 +347,9 @@ func (ks *scaler) scale(ctx context.Context, pa *autoscalingv1alpha1.PodAutoscal
 	// Also ignore initialScale if the revision is unreachable (routingState = "reserve"),
 	// allowing it to scale down to 0 immediately.
 	if initialScale > 1 && !pa.Status.IsScaleTargetInitialized() && pa.Spec.Reachability != autoscalingv1alpha1.ReachabilityUnreachable {
+		if maxScale > 0 && initialScale > maxScale {
+			initialScale = maxScale
+		}
 		// Ignore initial scale if minScale >= initialScale.
 		if minScale < initialScale {
 			logger.Debugf("Adjusting minScale to meet the initial scale: %d -> %d", minScale, initialScale)

pkg/reconciler/autoscaling/kpa/scaler_test.go

@@ -490,6 +490,17 @@ func TestScaler(t *testing.T) {
 			paMarkActivating(k, time.Now())
 			k.Annotations[autoscaling.InitialScaleAnnotationKey] = "5"
 		},
+	}, {
+		label:         "initial scale does not exceed maxScale",
+		startReplicas: 0,
+		scaleTo:       1,
+		maxScale:      2,
+		wantReplicas:  2,
+		wantScaling:   true,
+		paMutation: func(k *autoscalingv1alpha1.PodAutoscaler) {
+			paMarkActivating(k, time.Now())
+			k.Annotations[autoscaling.InitialScaleAnnotationKey] = "5"
+		},
 	}, {
 		label:         "reaching initial scale zero",
 		startReplicas: 0,
@@ -504,6 +515,52 @@ func TestScaler(t *testing.T) {
 		configMutator: func(c *config.Config) {
 			c.Autoscaler.AllowZeroInitialScale = true
 		},
+	}, {
+		label:         "initial scale with maxScale = 0 (unlimited)",
+		startReplicas: 0,
+		scaleTo:       1,
+		maxScale:      0,
+		wantReplicas:  5,
+		wantScaling:   true,
+		paMutation: func(k *autoscalingv1alpha1.PodAutoscaler) {
+			paMarkActivating(k, time.Now())
+			k.Annotations[autoscaling.InitialScaleAnnotationKey] = "5"
+		},
+	}, {
+		label:         "initial scale <= 1 respects desired scale within maxScale",
+		startReplicas: 0,
+		scaleTo:       1,
+		maxScale:      2,
+		wantReplicas:  1,
+		wantScaling:   true,
+		paMutation: func(k *autoscalingv1alpha1.PodAutoscaler) {
+			paMarkActivating(k, time.Now())
+			k.Annotations[autoscaling.InitialScaleAnnotationKey] = "1"
+		},
+	}, {
+		label:         "minScale < maxScale < initialScale clamps to maxScale",
+		startReplicas: 0,
+		scaleTo:       1,
+		minScale:      2,
+		maxScale:      4,
+		wantReplicas:  4,
+		wantScaling:   true,
+		paMutation: func(k *autoscalingv1alpha1.PodAutoscaler) {
+			paMarkActivating(k, time.Now())
+			k.Annotations[autoscaling.InitialScaleAnnotationKey] = "6"
+		},
+	}, {
+		label:         "initialScale < minScale < maxScale respects minScale",
+		startReplicas: 0,
+		scaleTo:       1,
+		minScale:      3,
+		maxScale:      5,
+		wantReplicas:  3,
+		wantScaling:   true,
+		paMutation: func(k *autoscalingv1alpha1.PodAutoscaler) {
+			paMarkActivating(k, time.Now())
+			k.Annotations[autoscaling.InitialScaleAnnotationKey] = "2"
+		},
 	}, {
 		label:         "unreachable revision with initialScale > 1 can scale to 0",
 		startReplicas: 2,
@@ -517,6 +574,32 @@ func TestScaler(t *testing.T) {
 			// Mark as unreachable (routingState = "reserve")
 			k.Spec.Reachability = autoscalingv1alpha1.ReachabilityUnreachable
 		},
+	}, {
+		label:         "unreachable revision with initialScale > maxScale can scale to 0",
+		startReplicas: 2,
+		scaleTo:       0,
+		maxScale:      2,
+		wantReplicas:  1, // First we deactivate and scale to 1.
+		wantScaling:   true,
+		wantCBCount:   1,
+		paMutation: func(k *autoscalingv1alpha1.PodAutoscaler) {
+			paMarkActive(k, time.Now().Add(-2*time.Minute))
+			k.Annotations[autoscaling.InitialScaleAnnotationKey] = "5"
+			// Mark as unreachable (routingState = "reserve")
+			k.Spec.Reachability = autoscalingv1alpha1.ReachabilityUnreachable
+		},
+	}, {
+		label:         "already initialized scale target ignores initialScale exceeding maxScale",
+		startReplicas: 2,
+		scaleTo:       1,
+		maxScale:      2,
+		wantReplicas:  1,
+		wantScaling:   true,
+		paMutation: func(k *autoscalingv1alpha1.PodAutoscaler) {
+			paMarkActive(k, time.Now().Add(-2*time.Minute))
+			k.Status.MarkScaleTargetInitialized()
+			k.Annotations[autoscaling.InitialScaleAnnotationKey] = "5"
+		},
 	}}
 
 	for _, test := range tests {