container: cover the status that has not caught up with the scale request

Turn the scale-from-zero regression into a table so it covers both the pre-scale read and a status the controller has not written yet, and give the type assertion in the reactor the SAFETY comment the lint gate wants.

pkg/executor/executortype/container/deployment_test.go

@@ -310,12 +310,48 @@ func TestContainerGetResources(t *testing.T) {
 }
 
 // TestContainerScaleFromZeroWaitsForAvailability covers the scale-to-zero race
-// reported in #3183. The first read reports one available replica (the pod the
+// reported in #3183. On the scale-from-zero path the deployment status can
-// idle reaper is tearing down) and every later read reports none, so a caller
+// still describe the pod the idle reaper is tearing down, either because it
-// that trusts the pre-scale status reports success with no serving pod.
+// was read before the scale request or because the controller has not written
+// a status for that request yet. A caller that trusts such a status reports
+// success while the Service has no endpoint and the router forwards into it.
 func TestContainerScaleFromZeroWaitsForAvailability(t *testing.T) {
 	t.Parallel()
 
+	// Generation of the spec after the scale request.
+	const generation = 2
+
+	tests := []struct {
+		name string
+		// status is the deployment status served by the nth read, 1-based.
+		status func(read int) appsv1.DeploymentStatus
+	}{
+		{
+			// The copy createOrGetDeployment read before scaling up.
+			name: "pre-scale read still counts the terminating pod",
+			status: func(read int) appsv1.DeploymentStatus {
+				available := int32(0)
+				if read == 1 {
+					available = 1
+				}
+				return appsv1.DeploymentStatus{ObservedGeneration: generation, AvailableReplicas: available}
+			},
+		},
+		{
+			// Status is written asynchronously by the deployment controller, so
+			// every read up to the deadline can still describe the generation
+			// before the scale request.
+			name: "status has not caught up with the scale request",
+			status: func(int) appsv1.DeploymentStatus {
+				return appsv1.DeploymentStatus{ObservedGeneration: generation - 1, AvailableReplicas: 1}
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
 			fn := newTestContainerFunction()
 			fn.Spec.PodSpec.Containers[0].Ports = []apiv1.ContainerPort{{ContainerPort: 8080}}
 			fn.Spec.InvokeStrategy.ExecutionStrategy.MinScale = 0
@@ -326,20 +362,18 @@ func TestContainerScaleFromZeroWaitsForAvailability(t *testing.T) {
 				ObjectMeta: metav1.ObjectMeta{
 					Name:        "ctr-fn",
 					Namespace:   ns,
+					Generation:  generation,
 					Annotations: map[string]string{fv1.EXECUTOR_INSTANCEID_LABEL: "test-instance"},
 				},
 				Spec: appsv1.DeploymentSpec{Replicas: &zero},
-		Status: appsv1.DeploymentStatus{AvailableReplicas: 0},
 			}
 
 			kubeClient := fake.NewClientset(scaledIn)
 			var reads int
-	kubeClient.PrependReactor("get", "deployments", func(action k8stesting.Action) (bool, runtime.Object, error) {
+			kubeClient.PrependReactor("get", "deployments", func(k8stesting.Action) (bool, runtime.Object, error) {
 				depl := scaledIn.DeepCopy()
 				reads++
-		if reads == 1 {
+				depl.Status = tt.status(reads)
-			depl.Status.AvailableReplicas = 1
-		}
 				return true, depl, nil
 			})
 			// The fake clientset has no built-in scale subresource for deployments.
@@ -347,6 +381,7 @@ func TestContainerScaleFromZeroWaitsForAvailability(t *testing.T) {
 				if action.GetSubresource() != "scale" {
 					return false, nil, nil
 				}
+				// SAFETY: this reactor is registered for "update" and returns early unless the subresource is scale, so the action is an UpdateAction.
 				return true, action.(k8stesting.UpdateAction).GetObject(), nil
 			})
 
@@ -358,8 +393,8 @@ func TestContainerScaleFromZeroWaitsForAvailability(t *testing.T) {
 				runtimeImagePullPolicy: apiv1.PullIfNotPresent,
 			}
 
-	// The deployment never becomes available in the fake cluster, so a correct
+			// The deployment never becomes available in the fake cluster, so a
-	// implementation runs the readiness wait out to this deadline.
+			// correct implementation runs the readiness wait out to this deadline.
 			ctx, cancel := context.WithTimeout(t.Context(), 2*time.Second)
 			defer cancel()
 
@@ -367,4 +402,6 @@ func TestContainerScaleFromZeroWaitsForAvailability(t *testing.T) {
 			require.Error(t, err, "scale-from-zero must not report success while no replica is available")
 			assert.ErrorIs(t, err, context.DeadlineExceeded,
 				"expected the readiness wait to run to its deadline, got: %v", err)
+		})
+	}
 }