ReplicaSet controller should count terminating pods in the status

pkg/controller/controller_utils.go

@@ -973,6 +973,21 @@ func compareMaxContainerRestarts(pi *v1.Pod, pj *v1.Pod) *bool {
 	return nil
 }
 
+// FilterClaimedPods returns pods that are controlled by the controller and match the selector.
+func FilterClaimedPods(controller metav1.Object, selector labels.Selector, pods []*v1.Pod) []*v1.Pod {
+	var result []*v1.Pod
+	for _, pod := range pods {
+		if !metav1.IsControlledBy(pod, controller) {
+			// It's an orphan or owned by someone else.
+			continue
+		}
+		if selector.Matches(labels.Set(pod.Labels)) {
+			result = append(result, pod)
+		}
+	}
+	return result
+}
+
 // FilterActivePods returns pods that have not terminated.
 func FilterActivePods(logger klog.Logger, pods []*v1.Pod) []*v1.Pod {
 	var result []*v1.Pod

pkg/controller/controller_utils_test.go

@@ -55,6 +55,7 @@ import (
 	"k8s.io/kubernetes/test/utils/ktesting"
 	testingclock "k8s.io/utils/clock/testing"
 	"k8s.io/utils/pointer"
+	"k8s.io/utils/ptr"
 
 	"github.com/google/go-cmp/cmp"
 	"github.com/stretchr/testify/assert"
@@ -433,6 +434,128 @@ func TestCountTerminatingPods(t *testing.T) {
 	assert.Len(t, terminatingList, int(2))
 }
 
+func TestClaimedPodFiltering(t *testing.T) {
+	rsUUID := uuid.NewUUID()
+
+	type podData struct {
+		podName         string
+		ownerReferences []metav1.OwnerReference
+		labels          map[string]string
+	}
+
+	type test struct {
+		name         string
+		pods         []podData
+		wantPodNames []string
+	}
+
+	tests := []test{
+		{
+			name: "Filters claimed pods",
+			pods: []podData{
+				// single owner reference
+				{podName: "claimed-1", labels: map[string]string{"foo": "bar"}, ownerReferences: []metav1.OwnerReference{
+					{UID: rsUUID, Controller: ptr.To(true)},
+				}},
+				{podName: "wrong-selector-1", labels: map[string]string{"foo": "baz"}, ownerReferences: []metav1.OwnerReference{
+					{UID: rsUUID, Controller: ptr.To(true)},
+				}},
+				{podName: "non-controller-1", labels: map[string]string{"foo": "bar"}, ownerReferences: []metav1.OwnerReference{
+					{UID: rsUUID, Controller: nil},
+				}},
+				{podName: "other-controller-1", labels: map[string]string{"foo": "bar"}, ownerReferences: []metav1.OwnerReference{
+					{UID: uuid.NewUUID(), Controller: ptr.To(true)},
+				}},
+				{podName: "other-workload-1", labels: map[string]string{"foo": "bee"}, ownerReferences: []metav1.OwnerReference{
+					{UID: uuid.NewUUID(), Controller: ptr.To(true)},
+				}},
+				{podName: "standalone-pod-1", labels: map[string]string{"foo": "beetle"}, ownerReferences: []metav1.OwnerReference{}},
+				// additional controller owner reference set to controller=false
+				{podName: "claimed-2", labels: map[string]string{"foo": "bar"}, ownerReferences: []metav1.OwnerReference{
+					{UID: uuid.NewUUID(), Controller: ptr.To(false)},
+					{UID: rsUUID, Controller: ptr.To(true)},
+				}},
+				{podName: "wrong-selector-2", labels: map[string]string{"foo": "baz"}, ownerReferences: []metav1.OwnerReference{
+					{UID: uuid.NewUUID(), Controller: ptr.To(false)},
+					{UID: rsUUID, Controller: ptr.To(true)},
+				}},
+				{podName: "non-controller-2", labels: map[string]string{"foo": "bar"}, ownerReferences: []metav1.OwnerReference{
+					{UID: uuid.NewUUID(), Controller: ptr.To(false)},
+					{UID: rsUUID, Controller: ptr.To(false)},
+				}},
+				{podName: "other-controller-2", labels: map[string]string{"foo": "bar"}, ownerReferences: []metav1.OwnerReference{
+					{UID: uuid.NewUUID(), Controller: ptr.To(false)},
+					{UID: uuid.NewUUID(), Controller: ptr.To(true)},
+				}},
+				{podName: "other-workload-1", labels: map[string]string{"foo": "bee"}, ownerReferences: []metav1.OwnerReference{
+					{UID: uuid.NewUUID(), Controller: ptr.To(false)},
+					{UID: uuid.NewUUID(), Controller: ptr.To(true)},
+				}},
+				{podName: "standalone-pod-1", labels: map[string]string{"foo": "beetle"}, ownerReferences: []metav1.OwnerReference{
+					{UID: uuid.NewUUID(), Controller: ptr.To(false)},
+				}},
+				// additional controller owner reference set to controller=nil
+				{podName: "claimed-3", labels: map[string]string{"foo": "bar"}, ownerReferences: []metav1.OwnerReference{
+					{UID: uuid.NewUUID()},
+					{UID: rsUUID, Controller: ptr.To(true)},
+				}},
+				{podName: "wrong-selector-3", labels: nil, ownerReferences: []metav1.OwnerReference{
+					{UID: uuid.NewUUID()},
+					{UID: rsUUID, Controller: ptr.To(true)},
+				}},
+				{podName: "non-controller-3", labels: map[string]string{"foo": "bar"}, ownerReferences: []metav1.OwnerReference{
+					{UID: uuid.NewUUID()},
+					{UID: rsUUID, Controller: nil},
+				}},
+				{podName: "other-controller-3", labels: map[string]string{"foo": "bar"}, ownerReferences: []metav1.OwnerReference{
+					{UID: uuid.NewUUID()},
+					{UID: uuid.NewUUID(), Controller: ptr.To(true)},
+				}},
+				{podName: "other-workload-1", labels: map[string]string{"foo": "bee"}, ownerReferences: []metav1.OwnerReference{
+					{UID: uuid.NewUUID()},
+				}},
+				{podName: "standalone-pod-1", labels: map[string]string{"foo": "beetle"}, ownerReferences: []metav1.OwnerReference{
+					{UID: uuid.NewUUID()},
+				}},
+			},
+			wantPodNames: []string{"claimed-1", "claimed-2", "claimed-3"},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			// This rc is not needed by the test, only the newPodList to give the pods labels/a namespace.
+			rs := newReplicaSet("test-claim", 3, rsUUID)
+			var pods []*v1.Pod
+			for _, p := range test.pods {
+				pods = append(pods, &v1.Pod{
+					ObjectMeta: metav1.ObjectMeta{
+						Name:            p.podName,
+						Namespace:       rs.Namespace,
+						Labels:          p.labels,
+						OwnerReferences: p.ownerReferences,
+					},
+					Status: v1.PodStatus{Phase: v1.PodRunning},
+				})
+			}
+
+			selector, err := metav1.LabelSelectorAsSelector(rs.Spec.Selector)
+			if err != nil {
+				t.Fatalf("Couldn't get selector for object %#v: %v", rs, err)
+			}
+			got := FilterClaimedPods(rs, selector, pods)
+			gotNames := sets.NewString()
+			for _, pod := range got {
+				gotNames.Insert(pod.Name)
+			}
+
+			if diff := cmp.Diff(test.wantPodNames, gotNames.List()); diff != "" {
+				t.Errorf("Active pod names (-want,+got):\n%s", diff)
+			}
+		})
+	}
+}
+
 func TestActivePodFiltering(t *testing.T) {
 	logger, _ := ktesting.NewTestContext(t)
 	type podData struct {

pkg/controller/replicaset/replica_set.go

@@ -45,6 +45,7 @@ import (
 	"k8s.io/apimachinery/pkg/types"
 	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
 	"k8s.io/apimachinery/pkg/util/wait"
+	utilfeature "k8s.io/apiserver/pkg/util/feature"
 	appsinformers "k8s.io/client-go/informers/apps/v1"
 	coreinformers "k8s.io/client-go/informers/core/v1"
 	clientset "k8s.io/client-go/kubernetes"
@@ -60,6 +61,7 @@ import (
 	podutil "k8s.io/kubernetes/pkg/api/v1/pod"
 	"k8s.io/kubernetes/pkg/controller"
 	"k8s.io/kubernetes/pkg/controller/replicaset/metrics"
+	"k8s.io/kubernetes/pkg/features"
 )
 
 const (
@@ -564,10 +566,10 @@ func (rsc *ReplicaSetController) processNextWorkItem(ctx context.Context) bool {
 }
 
 // manageReplicas checks and updates replicas for the given ReplicaSet.
-// Does NOT modify <filteredPods>.
+// Does NOT modify <activePods>.
 // It will requeue the replica set in case of an error while creating/deleting pods.
-func (rsc *ReplicaSetController) manageReplicas(ctx context.Context, filteredPods []*v1.Pod, rs *apps.ReplicaSet) error {
-	diff := len(filteredPods) - int(*(rs.Spec.Replicas))
+func (rsc *ReplicaSetController) manageReplicas(ctx context.Context, activePods []*v1.Pod, rs *apps.ReplicaSet) error {
+	diff := len(activePods) - int(*(rs.Spec.Replicas))
 	rsKey, err := controller.KeyFunc(rs)
 	if err != nil {
 		utilruntime.HandleError(fmt.Errorf("couldn't get key for %v %#v: %v", rsc.Kind, rs, err))
@@ -627,7 +629,7 @@ func (rsc *ReplicaSetController) manageReplicas(ctx context.Context, filteredPod
 		utilruntime.HandleError(err)
 
 		// Choose which Pods to delete, preferring those in earlier phases of startup.
-		podsToDelete := getPodsToDelete(filteredPods, relatedPods, diff)
+		podsToDelete := getPodsToDelete(activePods, relatedPods, diff)
 
 		// Snapshot the UIDs (ns/name) of the pods we're expecting to see
 		// deleted, so we know to record their expectations exactly once either
@@ -707,22 +709,27 @@ func (rsc *ReplicaSetController) syncReplicaSet(ctx context.Context, key string)
 	if err != nil {
 		return err
 	}
-	// Ignore inactive pods.
-	filteredPods := controller.FilterActivePods(logger, allPods)
 
-	// NOTE: filteredPods are pointing to objects from cache - if you need to
+	// NOTE: activePods and terminatingPods are pointing to objects from cache - if you need to
 	// modify them, you need to copy it first.
-	filteredPods, err = rsc.claimPods(ctx, rs, selector, filteredPods)
+	allActivePods := controller.FilterActivePods(logger, allPods)
+	activePods, err := rsc.claimPods(ctx, rs, selector, allActivePods)
 	if err != nil {
 		return err
 	}
 
+	var terminatingPods []*v1.Pod
+	if utilfeature.DefaultFeatureGate.Enabled(features.DeploymentPodReplacementPolicy) {
+		allTerminatingPods := controller.FilterTerminatingPods(allPods)
+		terminatingPods = controller.FilterClaimedPods(rs, selector, allTerminatingPods)
+	}
+
 	var manageReplicasErr error
 	if rsNeedsSync && rs.DeletionTimestamp == nil {
-		manageReplicasErr = rsc.manageReplicas(ctx, filteredPods, rs)
+		manageReplicasErr = rsc.manageReplicas(ctx, activePods, rs)
 	}
 	rs = rs.DeepCopy()
-	newStatus := calculateStatus(rs, filteredPods, manageReplicasErr)
+	newStatus := calculateStatus(rs, activePods, terminatingPods, manageReplicasErr)
 
 	// Always updates status as pods come up or die.
 	updatedRS, err := updateReplicaSetStatus(logger, rsc.kubeClient.AppsV1().ReplicaSets(rs.Namespace), rs, newStatus)

pkg/controller/replicaset/replica_set_utils.go

@@ -29,8 +29,11 @@ import (
 	v1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/labels"
+	utilfeature "k8s.io/apiserver/pkg/util/feature"
 	appsclient "k8s.io/client-go/kubernetes/typed/apps/v1"
 	podutil "k8s.io/kubernetes/pkg/api/v1/pod"
+	"k8s.io/kubernetes/pkg/features"
+	"k8s.io/utils/ptr"
 )
 
 // updateReplicaSetStatus attempts to update the Status.Replicas of the given ReplicaSet, with a single GET/PUT retry.
@@ -42,6 +45,7 @@ func updateReplicaSetStatus(logger klog.Logger, c appsclient.ReplicaSetInterface
 		rs.Status.FullyLabeledReplicas == newStatus.FullyLabeledReplicas &&
 		rs.Status.ReadyReplicas == newStatus.ReadyReplicas &&
 		rs.Status.AvailableReplicas == newStatus.AvailableReplicas &&
+		ptr.Equal(rs.Status.TerminatingReplicas, newStatus.TerminatingReplicas) &&
 		rs.Generation == rs.Status.ObservedGeneration &&
 		reflect.DeepEqual(rs.Status.Conditions, newStatus.Conditions) {
 		return rs, nil
@@ -56,11 +60,16 @@ func updateReplicaSetStatus(logger klog.Logger, c appsclient.ReplicaSetInterface
 	var getErr, updateErr error
 	var updatedRS *apps.ReplicaSet
 	for i, rs := 0, rs; ; i++ {
+		terminatingReplicasUpdateInfo := ""
+		if utilfeature.DefaultFeatureGate.Enabled(features.DeploymentPodReplacementPolicy) {
+			terminatingReplicasUpdateInfo = fmt.Sprintf("terminatingReplicas %s->%s, ", derefInt32ToStr(rs.Status.TerminatingReplicas), derefInt32ToStr(newStatus.TerminatingReplicas))
+		}
 		logger.V(4).Info(fmt.Sprintf("Updating status for %v: %s/%s, ", rs.Kind, rs.Namespace, rs.Name) +
 			fmt.Sprintf("replicas %d->%d (need %d), ", rs.Status.Replicas, newStatus.Replicas, *(rs.Spec.Replicas)) +
 			fmt.Sprintf("fullyLabeledReplicas %d->%d, ", rs.Status.FullyLabeledReplicas, newStatus.FullyLabeledReplicas) +
 			fmt.Sprintf("readyReplicas %d->%d, ", rs.Status.ReadyReplicas, newStatus.ReadyReplicas) +
 			fmt.Sprintf("availableReplicas %d->%d, ", rs.Status.AvailableReplicas, newStatus.AvailableReplicas) +
+			terminatingReplicasUpdateInfo +
 			fmt.Sprintf("sequence No: %v->%v", rs.Status.ObservedGeneration, newStatus.ObservedGeneration))
 
 		rs.Status = newStatus
@@ -83,18 +92,18 @@ func updateReplicaSetStatus(logger klog.Logger, c appsclient.ReplicaSetInterface
 	return nil, updateErr
 }
 
-func calculateStatus(rs *apps.ReplicaSet, filteredPods []*v1.Pod, manageReplicasErr error) apps.ReplicaSetStatus {
+func calculateStatus(rs *apps.ReplicaSet, activePods []*v1.Pod, terminatingPods []*v1.Pod, manageReplicasErr error) apps.ReplicaSetStatus {
 	newStatus := rs.Status
 	// Count the number of pods that have labels matching the labels of the pod
 	// template of the replica set, the matching pods may have more
 	// labels than are in the template. Because the label of podTemplateSpec is
 	// a superset of the selector of the replica set, so the possible
-	// matching pods must be part of the filteredPods.
+	// matching pods must be part of the activePods.
 	fullyLabeledReplicasCount := 0
 	readyReplicasCount := 0
 	availableReplicasCount := 0
 	templateLabel := labels.Set(rs.Spec.Template.Labels).AsSelectorPreValidated()
-	for _, pod := range filteredPods {
+	for _, pod := range activePods {
 		if templateLabel.Matches(labels.Set(pod.Labels)) {
 			fullyLabeledReplicasCount++
 		}
@@ -106,10 +115,15 @@ func calculateStatus(rs *apps.ReplicaSet, filteredPods []*v1.Pod, manageReplicas
 		}
 	}
 
+	var terminatingReplicasCount *int32
+	if utilfeature.DefaultFeatureGate.Enabled(features.DeploymentPodReplacementPolicy) {
+		terminatingReplicasCount = ptr.To(int32(len(terminatingPods)))
+	}
+
 	failureCond := GetCondition(rs.Status, apps.ReplicaSetReplicaFailure)
 	if manageReplicasErr != nil && failureCond == nil {
 		var reason string
-		if diff := len(filteredPods) - int(*(rs.Spec.Replicas)); diff < 0 {
+		if diff := len(activePods) - int(*(rs.Spec.Replicas)); diff < 0 {
 			reason = "FailedCreate"
 		} else if diff > 0 {
 			reason = "FailedDelete"
@@ -120,10 +134,11 @@ func calculateStatus(rs *apps.ReplicaSet, filteredPods []*v1.Pod, manageReplicas
 		RemoveCondition(&newStatus, apps.ReplicaSetReplicaFailure)
 	}
 
-	newStatus.Replicas = int32(len(filteredPods))
+	newStatus.Replicas = int32(len(activePods))
 	newStatus.FullyLabeledReplicas = int32(fullyLabeledReplicasCount)
 	newStatus.ReadyReplicas = int32(readyReplicasCount)
 	newStatus.AvailableReplicas = int32(availableReplicasCount)
+	newStatus.TerminatingReplicas = terminatingReplicasCount
 	return newStatus
 }
 
@@ -175,3 +190,10 @@ func filterOutCondition(conditions []apps.ReplicaSetCondition, condType apps.Rep
 	}
 	return newConditions
 }
+
+func derefInt32ToStr(ptr *int32) string {
+	if ptr == nil {
+		return "nil"
+	}
+	return fmt.Sprintf("%d", *ptr)
+}

pkg/controller/replicaset/replica_set_utils_test.go

@@ -25,6 +25,11 @@ import (
 
 	apps "k8s.io/api/apps/v1"
 	"k8s.io/api/core/v1"
+	meta "k8s.io/apimachinery/pkg/apis/meta/v1"
+	utilfeature "k8s.io/apiserver/pkg/util/feature"
+	featuregatetesting "k8s.io/component-base/featuregate/testing"
+	"k8s.io/kubernetes/pkg/features"
+	"k8s.io/utils/ptr"
 )
 
 func TestCalculateStatus(t *testing.T) {
@@ -36,113 +41,199 @@ func TestCalculateStatus(t *testing.T) {
 	longMinReadySecondsRS := newReplicaSet(1, fullLabelMap)
 	longMinReadySecondsRS.Spec.MinReadySeconds = 3600
 
+	asTerminating := func(pod *v1.Pod) *v1.Pod {
+		pod.DeletionTimestamp = ptr.To(meta.Now())
+		return pod
+	}
+
 	rsStatusTests := []struct {
-		name                     string
-		replicaset               *apps.ReplicaSet
-		filteredPods             []*v1.Pod
-		expectedReplicaSetStatus apps.ReplicaSetStatus
+		name                                 string
+		enableDeploymentPodReplacementPolicy bool
+		replicaset                           *apps.ReplicaSet
+		activePods                           []*v1.Pod
+		terminatingPods                      []*v1.Pod
+		expectedReplicaSetStatus             apps.ReplicaSetStatus
 	}{
 		{
 			"1 fully labelled pod",
+			false,
 			fullyLabelledRS,
 			[]*v1.Pod{
 				newPod("pod1", fullyLabelledRS, v1.PodRunning, nil, true),
 			},
+			nil,
 			apps.ReplicaSetStatus{
 				Replicas:             1,
 				FullyLabeledReplicas: 1,
 				ReadyReplicas:        1,
 				AvailableReplicas:    1,
+				TerminatingReplicas:  nil,
 			},
 		},
 		{
 			"1 not fully labelled pod",
+			false,
 			notFullyLabelledRS,
 			[]*v1.Pod{
 				newPod("pod1", notFullyLabelledRS, v1.PodRunning, nil, true),
 			},
+			nil,
 			apps.ReplicaSetStatus{
 				Replicas:             1,
 				FullyLabeledReplicas: 0,
 				ReadyReplicas:        1,
 				AvailableReplicas:    1,
+				TerminatingReplicas:  nil,
 			},
 		},
 		{
 			"2 fully labelled pods",
+			false,
 			fullyLabelledRS,
 			[]*v1.Pod{
 				newPod("pod1", fullyLabelledRS, v1.PodRunning, nil, true),
 				newPod("pod2", fullyLabelledRS, v1.PodRunning, nil, true),
 			},
+			nil,
 			apps.ReplicaSetStatus{
 				Replicas:             2,
 				FullyLabeledReplicas: 2,
 				ReadyReplicas:        2,
 				AvailableReplicas:    2,
+				TerminatingReplicas:  nil,
+			},
+		},
+		{
+			"2 fully labelled pods with DeploymentPodReplacementPolicy",
+			true,
+			fullyLabelledRS,
+			[]*v1.Pod{
+				newPod("pod1", fullyLabelledRS, v1.PodRunning, nil, true),
+				newPod("pod2", fullyLabelledRS, v1.PodRunning, nil, true),
+			},
+			nil,
+			apps.ReplicaSetStatus{
+				Replicas:             2,
+				FullyLabeledReplicas: 2,
+				ReadyReplicas:        2,
+				AvailableReplicas:    2,
+				TerminatingReplicas:  ptr.To[int32](0),
 			},
 		},
 		{
 			"2 not fully labelled pods",
+			false,
 			notFullyLabelledRS,
 			[]*v1.Pod{
 				newPod("pod1", notFullyLabelledRS, v1.PodRunning, nil, true),
 				newPod("pod2", notFullyLabelledRS, v1.PodRunning, nil, true),
 			},
+			nil,
 			apps.ReplicaSetStatus{
 				Replicas:             2,
 				FullyLabeledReplicas: 0,
 				ReadyReplicas:        2,
 				AvailableReplicas:    2,
+				TerminatingReplicas:  nil,
 			},
 		},
 		{
 			"1 fully labelled pod, 1 not fully labelled pod",
+			false,
 			notFullyLabelledRS,
 			[]*v1.Pod{
 				newPod("pod1", notFullyLabelledRS, v1.PodRunning, nil, true),
 				newPod("pod2", fullyLabelledRS, v1.PodRunning, nil, true),
 			},
+			nil,
 			apps.ReplicaSetStatus{
 				Replicas:             2,
 				FullyLabeledReplicas: 1,
 				ReadyReplicas:        2,
 				AvailableReplicas:    2,
+				TerminatingReplicas:  nil,
 			},
 		},
 		{
 			"1 non-ready pod",
+			false,
 			fullyLabelledRS,
 			[]*v1.Pod{
 				newPod("pod1", fullyLabelledRS, v1.PodPending, nil, true),
 			},
+			nil,
 			apps.ReplicaSetStatus{
 				Replicas:             1,
 				FullyLabeledReplicas: 1,
 				ReadyReplicas:        0,
 				AvailableReplicas:    0,
+				TerminatingReplicas:  nil,
 			},
 		},
 		{
 			"1 ready but non-available pod",
+			false,
 			longMinReadySecondsRS,
 			[]*v1.Pod{
 				newPod("pod1", longMinReadySecondsRS, v1.PodRunning, nil, true),
 			},
+			nil,
 			apps.ReplicaSetStatus{
 				Replicas:             1,
 				FullyLabeledReplicas: 1,
 				ReadyReplicas:        1,
 				AvailableReplicas:    0,
+				TerminatingReplicas:  nil,
+			},
+		},
+		{
+			"1 fully labelled pod and 1 terminating without DeploymentPodReplacementPolicy",
+			false,
+			fullyLabelledRS,
+			[]*v1.Pod{
+				newPod("pod1", fullyLabelledRS, v1.PodRunning, nil, true),
+			},
+			[]*v1.Pod{
+				asTerminating(newPod("pod2", fullyLabelledRS, v1.PodRunning, nil, true)),
+			},
+			apps.ReplicaSetStatus{
+				Replicas:             1,
+				FullyLabeledReplicas: 1,
+				ReadyReplicas:        1,
+				AvailableReplicas:    1,
+				TerminatingReplicas:  nil,
+			},
+		},
+		{
+			"1 fully labelled pods and 2 terminating with DeploymentPodReplacementPolicy",
+			true,
+			fullyLabelledRS,
+			[]*v1.Pod{
+				newPod("pod1", fullyLabelledRS, v1.PodRunning, nil, true),
+			},
+			[]*v1.Pod{
+				asTerminating(newPod("pod2", fullyLabelledRS, v1.PodRunning, nil, true)),
+				asTerminating(newPod("pod3", fullyLabelledRS, v1.PodRunning, nil, true)),
+			},
+			apps.ReplicaSetStatus{
+				Replicas:             1,
+				FullyLabeledReplicas: 1,
+				ReadyReplicas:        1,
+				AvailableReplicas:    1,
+				TerminatingReplicas:  ptr.To[int32](2),
 			},
 		},
 	}
 
 	for _, test := range rsStatusTests {
-		replicaSetStatus := calculateStatus(test.replicaset, test.filteredPods, nil)
-		if !reflect.DeepEqual(replicaSetStatus, test.expectedReplicaSetStatus) {
-			t.Errorf("%s: unexpected replicaset status: expected %v, got %v", test.name, test.expectedReplicaSetStatus, replicaSetStatus)
-		}
+		t.Run(test.name, func(t *testing.T) {
+			featuregatetesting.SetFeatureGateDuringTest(t, utilfeature.DefaultFeatureGate, features.DeploymentPodReplacementPolicy, test.enableDeploymentPodReplacementPolicy)
+
+			replicaSetStatus := calculateStatus(test.replicaset, test.activePods, test.terminatingPods, nil)
+			if !reflect.DeepEqual(replicaSetStatus, test.expectedReplicaSetStatus) {
+				t.Errorf("unexpected replicaset status: expected %v, got %v", test.expectedReplicaSetStatus, replicaSetStatus)
+			}
+		})
 	}
 }
 
@@ -160,7 +251,7 @@ func TestCalculateStatusConditions(t *testing.T) {
 	rsStatusConditionTests := []struct {
 		name                         string
 		replicaset                   *apps.ReplicaSet
-		filteredPods                 []*v1.Pod
+		activePods                   []*v1.Pod
 		manageReplicasErr            error
 		expectedReplicaSetConditions []apps.ReplicaSetCondition
 	}{
@@ -234,13 +325,15 @@ func TestCalculateStatusConditions(t *testing.T) {
 	}
 
 	for _, test := range rsStatusConditionTests {
-		replicaSetStatus := calculateStatus(test.replicaset, test.filteredPods, test.manageReplicasErr)
-		// all test cases have at most 1 status condition
-		if len(replicaSetStatus.Conditions) > 0 {
-			test.expectedReplicaSetConditions[0].LastTransitionTime = replicaSetStatus.Conditions[0].LastTransitionTime
-		}
-		if !reflect.DeepEqual(replicaSetStatus.Conditions, test.expectedReplicaSetConditions) {
-			t.Errorf("%s: unexpected replicaset status: expected %v, got %v", test.name, test.expectedReplicaSetConditions, replicaSetStatus.Conditions)
-		}
+		t.Run(test.name, func(t *testing.T) {
+			replicaSetStatus := calculateStatus(test.replicaset, test.activePods, nil, test.manageReplicasErr)
+			// all test cases have at most 1 status condition
+			if len(replicaSetStatus.Conditions) > 0 {
+				test.expectedReplicaSetConditions[0].LastTransitionTime = replicaSetStatus.Conditions[0].LastTransitionTime
+			}
+			if !reflect.DeepEqual(replicaSetStatus.Conditions, test.expectedReplicaSetConditions) {
+				t.Errorf("unexpected replicaset status: expected %v, got %v", test.expectedReplicaSetConditions, replicaSetStatus.Conditions)
+			}
+		})
 	}
 }

test/integration/replicaset/replicaset_test.go

@@ -208,6 +208,20 @@ func waitRSStable(t *testing.T, clientSet clientset.Interface, rs *apps.ReplicaS
 	}
 }
 
+// Verify .Status.TerminatingPods is equal to terminatingPods.
+func waitForTerminatingPods(clientSet clientset.Interface, ctx context.Context, rs *apps.ReplicaSet, terminatingPods *int32) error {
+	if err := wait.PollUntilContextTimeout(ctx, interval, timeout, true, func(c context.Context) (bool, error) {
+		newRS, err := clientSet.AppsV1().ReplicaSets(rs.Namespace).Get(c, rs.Name, metav1.GetOptions{})
+		if err != nil {
+			return false, err
+		}
+		return ptr.Equal(newRS.Status.TerminatingReplicas, terminatingPods), nil
+	}); err != nil {
+		return fmt.Errorf("failed to verify .Status.TerminatingPods is equal to %d for replicaset %q: %w", ptr.Deref(terminatingPods, -1), rs.Name, err)
+	}
+	return nil
+}
+
 // Update .Spec.Replicas to replicas and verify .Status.Replicas is changed accordingly
 func scaleRS(t *testing.T, c clientset.Interface, rs *apps.ReplicaSet, replicas int32) {
 	rsClient := c.AppsV1().ReplicaSets(rs.Namespace)
@@ -1056,3 +1070,72 @@ func TestReplicaSetsAppsV1DefaultGCPolicy(t *testing.T) {
 
 	_ = rsClient.Delete(tCtx, rs.Name, metav1.DeleteOptions{})
 }
+
+func TestTerminatingReplicas(t *testing.T) {
+	featuregatetesting.SetFeatureGateDuringTest(t, utilfeature.DefaultFeatureGate, features.DeploymentPodReplacementPolicy, false)
+
+	tCtx, closeFn, rm, informers, c := rmSetup(t)
+	defer closeFn()
+	ns := framework.CreateNamespaceOrDie(c, "test-terminating-replicas", t)
+	defer framework.DeleteNamespaceOrDie(c, ns, t)
+	stopControllers := runControllerAndInformers(t, rm, informers, 0)
+	defer stopControllers()
+
+	rs := newRS("rs", ns.Name, 5)
+	rs.Spec.Template.Spec.NodeName = "fake-node"
+	rs.Spec.Template.Spec.TerminationGracePeriodSeconds = ptr.To(int64(300))
+	rss, _ := createRSsPods(t, c, []*apps.ReplicaSet{rs}, []*v1.Pod{})
+	rs = rss[0]
+	waitRSStable(t, c, rs)
+	if err := waitForTerminatingPods(c, tCtx, rs, nil); err != nil {
+		t.Fatal(err)
+	}
+
+	podClient := c.CoreV1().Pods(ns.Name)
+	pods := getPods(t, podClient, labelMap())
+	if len(pods.Items) != 5 {
+		t.Fatalf("len(pods) = %d, want 5", len(pods.Items))
+	}
+	setPodsReadyCondition(t, c, pods, v1.ConditionTrue, time.Now())
+
+	// should not update terminating pods when feature gate is disabled
+	if err := podClient.Delete(tCtx, pods.Items[0].Name, metav1.DeleteOptions{}); err != nil {
+		t.Fatal(err)
+	}
+	waitRSStable(t, c, rs)
+	if err := waitForTerminatingPods(c, tCtx, rs, nil); err != nil {
+		t.Fatal(err)
+	}
+
+	// should update terminating pods when feature gate is enabled
+	featuregatetesting.SetFeatureGateDuringTest(t, utilfeature.DefaultFeatureGate, features.DeploymentPodReplacementPolicy, true)
+	if err := podClient.Delete(tCtx, pods.Items[1].Name, metav1.DeleteOptions{}); err != nil {
+		t.Fatal(err)
+	}
+	waitRSStable(t, c, rs)
+	if err := waitForTerminatingPods(c, tCtx, rs, ptr.To[int32](2)); err != nil {
+		t.Fatal(err)
+	}
+	// should update status when the pod is removed
+	if err := podClient.Delete(tCtx, pods.Items[0].Name, metav1.DeleteOptions{GracePeriodSeconds: ptr.To(int64(0))}); err != nil {
+		t.Fatal(err)
+	}
+	if err := waitForTerminatingPods(c, tCtx, rs, ptr.To[int32](1)); err != nil {
+		t.Fatal(err)
+	}
+
+	// should revert terminating pods to 0 when feature gate is disabled
+	featuregatetesting.SetFeatureGateDuringTest(t, utilfeature.DefaultFeatureGate, features.DeploymentPodReplacementPolicy, false)
+	if err := podClient.Delete(tCtx, pods.Items[2].Name, metav1.DeleteOptions{}); err != nil {
+		t.Fatal(err)
+	}
+	waitRSStable(t, c, rs)
+	if err := waitForTerminatingPods(c, tCtx, rs, nil); err != nil {
+		t.Fatal(err)
+	}
+	pods = getPods(t, podClient, labelMap())
+	// 5 non-terminating, 2 terminating
+	if len(pods.Items) != 7 {
+		t.Fatalf("len(pods) = %d, want 7", len(pods.Items))
+	}
+}