revision reachable when active. allow unreachable to scale to 0

pkg/apis/autoscaling/v1alpha1/pa_lifecycle.go

@@ -187,6 +187,14 @@ func (pa *PodAutoscaler) IsReady() bool {
 		pas.GetCondition(PodAutoscalerConditionReady).IsTrue()
 }
 
+func (pa *PodAutoscaler) IsUnreachable() bool {
+	return pa.Spec.Reachability == "Unreachable"
+}
+
+func (pa *PodAutoscaler) IsReachable() bool {
+	return pa.Spec.Reachability == "Reachable"
+}
+
 // IsActive returns true if the pod autoscaler has finished scaling.
 func (pas *PodAutoscalerStatus) IsActive() bool {
 	return pas.GetCondition(PodAutoscalerConditionActive).IsTrue()

pkg/autoscaler/scaling/autoscaler.go

@@ -163,7 +163,7 @@ func (a *autoscaler) Scale(logger *zap.SugaredLogger, now time.Time) ScaleResult
 		observedStableValue, observedPanicValue, err = a.metricClient.StableAndPanicConcurrency(metricKey, now)
 	}
 
-	if err != nil {
+	if err != nil && spec.Reachable {
 		if errors.Is(err, metrics.ErrNoData) {
 			logger.Debug("No data to scale on yet")
 		} else {

pkg/reconciler/autoscaling/kpa/kpa.go

@@ -270,14 +270,19 @@ func computeActiveCondition(ctx context.Context, pa *autoscalingv1alpha1.PodAuto
 		if pa.Status.IsActivating() && minReady > 0 {
 			// We only ever scale to zero while activating if we fail to activate within the progress deadline.
 			pa.Status.MarkInactive("TimedOut", "The target could not be activated.")
-		} else {
+		} else if !pa.Status.IsInactive() {
 			pa.Status.MarkInactive(noTrafficReason, "The target is not receiving traffic.")
 		}
 
 	case pc.ready < minReady:
 		if pc.want > 0 || !pa.Status.IsInactive() {
-			pa.Status.MarkActivating(
-				"Queued", "Requests to the target are being buffered as resources are provisioned.")
+			if pa.IsUnreachable() {
+				pa.Status.MarkInactive(
+					"Failed", "The target failed.")
+			} else {
+				pa.Status.MarkActivating(
+					"Queued", "Requests to the target are being buffered as resources are provisioned.")
+			}
 		} else {
 			// This is for the initialScale 0 case. In the first iteration, minReady is 0,
 			// but for the following iterations, minReady is 1. pc.want will continue being
@@ -286,7 +291,12 @@ func computeActiveCondition(ctx context.Context, pa *autoscalingv1alpha1.PodAuto
 			// still need to set it again. Otherwise reconciliation will fail with NewObservedGenFailure
 			// because we cannot go through one iteration of reconciliation without setting
 			// some status.
-			pa.Status.MarkInactive(noTrafficReason, "The target is not receiving traffic.")
+			if pa.Status.IsInactive() {
+				cond := pa.Status.GetCondition("Active")
+				pa.Status.MarkInactive(cond.Reason, cond.Message)
+			} else {
+				pa.Status.MarkInactive(noTrafficReason, "The target is not receiving traffic.")
+			}
 		}
 
 	case pc.ready >= minReady:

pkg/reconciler/revision/controller.go

@@ -24,25 +24,27 @@ import (
 
 	"go.uber.org/zap"
 	"golang.org/x/time/rate"
+	"k8s.io/client-go/tools/cache"
+	"k8s.io/client-go/util/workqueue"
 	cachingclient "knative.dev/caching/pkg/client/injection/client"
 	imageinformer "knative.dev/caching/pkg/client/injection/informers/caching/v1alpha1/image"
+	netcfg "knative.dev/networking/pkg/config"
 	"knative.dev/pkg/changeset"
 	kubeclient "knative.dev/pkg/client/injection/kube/client"
 	deploymentinformer "knative.dev/pkg/client/injection/kube/informers/apps/v1/deployment"
-	servingclient "knative.dev/serving/pkg/client/injection/client"
-	painformer "knative.dev/serving/pkg/client/injection/informers/autoscaling/v1alpha1/podautoscaler"
-	revisioninformer "knative.dev/serving/pkg/client/injection/informers/serving/v1/revision"
-	revisionreconciler "knative.dev/serving/pkg/client/injection/reconciler/serving/v1/revision"
-
-	"k8s.io/client-go/tools/cache"
-	"k8s.io/client-go/util/workqueue"
-	netcfg "knative.dev/networking/pkg/config"
+	podinformer "knative.dev/pkg/client/injection/kube/informers/core/v1/pod"
 	"knative.dev/pkg/configmap"
 	"knative.dev/pkg/controller"
 	"knative.dev/pkg/logging"
 	"knative.dev/pkg/metrics"
+	pkgreconciler "knative.dev/pkg/reconciler"
 	apisconfig "knative.dev/serving/pkg/apis/config"
+	"knative.dev/serving/pkg/apis/serving"
 	v1 "knative.dev/serving/pkg/apis/serving/v1"
+	servingclient "knative.dev/serving/pkg/client/injection/client"
+	painformer "knative.dev/serving/pkg/client/injection/informers/autoscaling/v1alpha1/podautoscaler"
+	revisioninformer "knative.dev/serving/pkg/client/injection/informers/serving/v1/revision"
+	revisionreconciler "knative.dev/serving/pkg/client/injection/reconciler/serving/v1/revision"
 	"knative.dev/serving/pkg/deployment"
 	"knative.dev/serving/pkg/reconciler/revision/config"
 )
@@ -73,6 +75,7 @@ func newControllerWithOptions(
 	deploymentInformer := deploymentinformer.Get(ctx)
 	imageInformer := imageinformer.Get(ctx)
 	paInformer := painformer.Get(ctx)
+	podsInformer := podinformer.Get(ctx)
 
 	c := &Reconciler{
 		kubeclient:    kubeclient.Get(ctx),
@@ -132,6 +135,11 @@ func newControllerWithOptions(
 	deploymentInformer.Informer().AddEventHandler(handleMatchingControllers)
 	paInformer.Informer().AddEventHandler(handleMatchingControllers)
 
+	podsInformer.Informer().AddEventHandler(cache.FilteringResourceEventHandler{
+		FilterFunc: pkgreconciler.LabelExistsFilterFunc(serving.RevisionLabelKey),
+		Handler:    controller.HandleAll(impl.EnqueueLabelOfNamespaceScopedResource("", serving.RevisionLabelKey)),
+	})
+
 	// We don't watch for changes to Image because we don't incorporate any of its
 	// properties into our own status and should work completely in the absence of
 	// a functioning Image controller.

pkg/reconciler/revision/resources/pa.go

@@ -57,15 +57,18 @@ func reachability(rev *v1.Revision) autoscalingv1alpha1.ReachabilityType {
 		v1.RevisionConditionContainerHealthy,
 	}
 
+	routingState := rev.GetRoutingState()
+	if routingState == v1.RoutingStateActive {
+		return autoscalingv1alpha1.ReachabilityReachable
+	}
+
 	for _, cond := range conds {
 		if c := rev.Status.GetCondition(cond); c != nil && c.IsFalse() {
 			return autoscalingv1alpha1.ReachabilityUnreachable
 		}
 	}
 
 	switch rev.GetRoutingState() {
-	case v1.RoutingStateActive:
-		return autoscalingv1alpha1.ReachabilityReachable
 	case v1.RoutingStateReserve:
 		return autoscalingv1alpha1.ReachabilityUnreachable
 	default: