refactor(pkg/descheduler): create fake shared informer factory only once

pkg/descheduler/descheduler.go

@@ -36,6 +36,7 @@ import (
 	schedulingv1 "k8s.io/api/scheduling/v1"
 	apierrors "k8s.io/apimachinery/pkg/api/errors"
 	"k8s.io/apimachinery/pkg/api/meta"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/labels"
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/runtime/schema"
@@ -133,6 +134,7 @@ func (c *evictedPodsCache) clear() {
 
 type descheduler struct {
 	rs                                *options.DeschedulerServer
+	client                            clientset.Interface
 	kubeClientSandbox                 *kubeClientSandbox
 	getPodsAssignedToNode             podutil.GetPodsAssignedToNodeFunc
 	sharedInformerFactory             informers.SharedInformerFactory
@@ -151,8 +153,6 @@ type descheduler struct {
 // kubeClientSandbox creates a sandbox environment with a fake client and informer factory
 // that mirrors resources from a real client, useful for dry-run testing scenarios
 type kubeClientSandbox struct {
-	client                 clientset.Interface
-	sharedInformerFactory  informers.SharedInformerFactory
 	fakeKubeClient         *fakeclientset.Clientset
 	fakeFactory            informers.SharedInformerFactory
 	resourceToInformer     map[schema.GroupVersionResource]informers.GenericInformer
@@ -173,13 +173,16 @@ func newDefaultKubeClientSandbox(client clientset.Interface, sharedInformerFacto
 
 func newKubeClientSandbox(client clientset.Interface, sharedInformerFactory informers.SharedInformerFactory, resources ...schema.GroupVersionResource) (*kubeClientSandbox, error) {
 	sandbox := &kubeClientSandbox{
-		client:                 client,
-		sharedInformerFactory:  sharedInformerFactory,
 		resourceToInformer:     make(map[schema.GroupVersionResource]informers.GenericInformer),
 		evictedPodsCache:       newEvictedPodsCache(),
 		podEvictionReactionFnc: podEvictionReactionFnc,
 	}
 
+	sandbox.fakeKubeClient = fakeclientset.NewSimpleClientset()
+	// simulate a pod eviction by deleting a pod
+	sandbox.fakeKubeClient.PrependReactor("create", "pods", sandbox.podEvictionReactionFnc(sandbox.fakeKubeClient, sandbox.evictedPodsCache))
+	sandbox.fakeFactory = informers.NewSharedInformerFactory(sandbox.fakeKubeClient, 0)
+
 	for _, resource := range resources {
 		informer, err := sharedInformerFactory.ForResource(resource)
 		if err != nil {
@@ -188,33 +191,78 @@ func newKubeClientSandbox(client clientset.Interface, sharedInformerFactory info
 		sandbox.resourceToInformer[resource] = informer
 	}
 
+	// Register event handlers to sync changes from real client to fake client.
+	// These handlers will keep the fake client in sync with ongoing changes.
+	if err := sandbox.registerEventHandlers(); err != nil {
+		return nil, fmt.Errorf("error registering event handlers: %w", err)
+	}
+
 	return sandbox, nil
 }
 
-func (sandbox *kubeClientSandbox) buildSandbox() error {
+func (sandbox *kubeClientSandbox) registerEventHandlers() error {
-	sandbox.fakeKubeClient = fakeclientset.NewSimpleClientset()
-	// simulate a pod eviction by deleting a pod
-	sandbox.fakeKubeClient.PrependReactor("create", "pods", sandbox.podEvictionReactionFnc(sandbox.fakeKubeClient, sandbox.evictedPodsCache))
-	sandbox.fakeFactory = informers.NewSharedInformerFactory(sandbox.fakeKubeClient, 0)
-
 	for resource, informer := range sandbox.resourceToInformer {
+		// Create a local copy to avoid closure capture issue
+		resource := resource
+
 		_, err := sandbox.fakeFactory.ForResource(resource)
 		if err != nil {
-			return fmt.Errorf("error getting resource %s: %w", resource, err)
+			return fmt.Errorf("error getting resource %s for fake factory: %w", resource, err)
 		}
 
-		objects, err := informer.Lister().List(labels.Everything())
+		_, err = informer.Informer().AddEventHandler(cache.ResourceEventHandlerFuncs{
+			AddFunc: func(obj interface{}) {
+				runtimeObj, ok := obj.(runtime.Object)
+				if !ok {
+					klog.ErrorS(nil, "object is not a runtime.Object", "resource", resource)
+					return
+				}
+				if err := sandbox.fakeKubeClient.Tracker().Add(runtimeObj); err != nil {
+					if !apierrors.IsAlreadyExists(err) {
+						klog.ErrorS(err, "failed to add object to fake client", "resource", resource)
+					}
+				}
+			},
+			UpdateFunc: func(oldObj, newObj interface{}) {
+				runtimeObj, ok := newObj.(runtime.Object)
+				if !ok {
+					klog.ErrorS(nil, "object is not a runtime.Object", "resource", resource)
+					return
+				}
+				metaObj, err := meta.Accessor(runtimeObj)
+				if err != nil {
+					klog.ErrorS(err, "failed to get object metadata", "resource", resource)
+					return
+				}
+				if err := sandbox.fakeKubeClient.Tracker().Update(resource, runtimeObj, metaObj.GetNamespace()); err != nil {
+					klog.ErrorS(err, "failed to update object in fake client", "resource", resource)
+				}
+			},
+			DeleteFunc: func(obj interface{}) {
+				// Handle tombstone case where the object might be wrapped
+				if tombstone, ok := obj.(cache.DeletedFinalStateUnknown); ok {
+					obj = tombstone.Obj
+				}
+
+				runtimeObj, ok := obj.(runtime.Object)
+				if !ok {
+					klog.ErrorS(nil, "object is not a runtime.Object", "resource", resource)
+					return
+				}
+				metaObj, err := meta.Accessor(runtimeObj)
+				if err != nil {
+					klog.ErrorS(err, "failed to get object metadata", "resource", resource)
+					return
+				}
+				if err := sandbox.fakeKubeClient.Tracker().Delete(resource, metaObj.GetNamespace(), metaObj.GetName()); err != nil {
+					klog.ErrorS(err, "failed to delete object from fake client", "resource", resource)
+				}
+			},
+		})
 		if err != nil {
-			return fmt.Errorf("error listing %s: %w", informer, err)
+			return fmt.Errorf("error adding event handler for resource %s: %w", resource, err)
-		}
-
-		for _, object := range objects {
-			if err := sandbox.fakeKubeClient.Tracker().Add(object); err != nil {
-				return fmt.Errorf("error adding object to tracker: %w", err)
-			}
 		}
 	}
-
 	return nil
 }
 
@@ -230,6 +278,161 @@ func (sandbox *kubeClientSandbox) reset() {
 	sandbox.evictedPodsCache.clear()
 }
 
+// hasObjectInIndexer checks if an object exists in the fake indexer for the specified resource
+func (sandbox *kubeClientSandbox) hasObjectInIndexer(resource schema.GroupVersionResource, namespace, name string) (bool, error) {
+	informer, err := sandbox.fakeFactory.ForResource(resource)
+	if err != nil {
+		return false, fmt.Errorf("error getting informer for resource %s: %w", resource, err)
+	}
+
+	key := cache.MetaObjectToName(&metav1.ObjectMeta{Namespace: namespace, Name: name}).String()
+	_, exists, err := informer.Informer().GetIndexer().GetByKey(key)
+	if err != nil {
+		return false, err
+	}
+
+	return exists, nil
+}
+
+// hasRuntimeObjectInIndexer checks if a runtime.Object exists in the fake indexer by detecting its resource type
+func (sandbox *kubeClientSandbox) hasRuntimeObjectInIndexer(obj runtime.Object) (bool, error) {
+	// Get metadata accessor to extract namespace and name
+	metaObj, err := meta.Accessor(obj)
+	if err != nil {
+		return false, fmt.Errorf("failed to get object metadata: %w", err)
+	}
+
+	// Get the GVK from the object using TypeMeta
+	gvk := obj.GetObjectKind().GroupVersionKind()
+	if gvk.Empty() {
+		return false, fmt.Errorf("no GroupVersionKind found for object")
+	}
+
+	// Use the GVK to construct the GVR by pluralizing the kind
+	plural, _ := meta.UnsafeGuessKindToResource(gvk)
+	gvr := schema.GroupVersionResource{
+		Group:    gvk.Group,
+		Version:  gvk.Version,
+		Resource: plural.Resource,
+	}
+
+	return sandbox.hasObjectInIndexer(gvr, metaObj.GetNamespace(), metaObj.GetName())
+}
+
+func waitForPodsCondition(ctx context.Context, pods []*evictedPodInfo, checkFn func(*evictedPodInfo) (bool, error), successMsg string) error {
+	if len(pods) == 0 {
+		return nil
+	}
+
+	err := wait.PollUntilContextTimeout(ctx, 100*time.Millisecond, 5*time.Second, true, func(ctx context.Context) (bool, error) {
+		for _, pod := range pods {
+			satisfied, err := checkFn(pod)
+			if err != nil {
+				return false, err
+			}
+			if !satisfied {
+				return false, nil
+			}
+		}
+		return true, nil
+	})
+	if err != nil {
+		return err
+	}
+
+	klog.V(4).InfoS(successMsg)
+	return nil
+}
+
+// restoreEvictedPods restores pods from the evicted pods cache back to the fake client
+func (sandbox *kubeClientSandbox) restoreEvictedPods(ctx context.Context) error {
+	podInformer, ok := sandbox.resourceToInformer[v1.SchemeGroupVersion.WithResource("pods")]
+	if !ok {
+		return fmt.Errorf("pod informer not found in resourceToInformer")
+	}
+
+	evictedPods := sandbox.evictedPodsCache.list()
+
+	// First wait loop: Check that all evicted pods are cleared from the indexers.
+	// This ensures the eviction has fully propagated through the fake informer's indexer.
+	if err := waitForPodsCondition(ctx, evictedPods, func(pod *evictedPodInfo) (bool, error) {
+		exists, err := sandbox.hasObjectInIndexer(v1.SchemeGroupVersion.WithResource("pods"), pod.Namespace, pod.Name)
+		if err != nil {
+			klog.V(4).InfoS("Error checking indexer for pod", "namespace", pod.Namespace, "name", pod.Name, "error", err)
+			return false, nil
+		}
+		if exists {
+			klog.V(4).InfoS("Pod still exists in fake indexer, waiting", "namespace", pod.Namespace, "name", pod.Name)
+			return false, nil
+		}
+		klog.V(4).InfoS("Pod no longer in fake indexer", "namespace", pod.Namespace, "name", pod.Name)
+		return true, nil
+	}, "All evicted pods removed from fake indexer"); err != nil {
+		return fmt.Errorf("timeout waiting for evicted pods to be removed from fake indexer: %w", err)
+	}
+
+	var restoredPods []*evictedPodInfo
+	for _, evictedPodInfo := range sandbox.evictedPodsCache.list() {
+		obj, err := podInformer.Lister().ByNamespace(evictedPodInfo.Namespace).Get(evictedPodInfo.Name)
+		if err != nil {
+			klog.V(3).InfoS("Pod not found in real client, skipping restoration", "namespace", evictedPodInfo.Namespace, "name", evictedPodInfo.Name, "error", err)
+			continue
+		}
+
+		pod, ok := obj.(*v1.Pod)
+		if !ok {
+			klog.ErrorS(nil, "Object is not a pod", "namespace", evictedPodInfo.Namespace, "name", evictedPodInfo.Name)
+			continue
+		}
+
+		if string(pod.UID) != evictedPodInfo.UID {
+			klog.V(3).InfoS("Pod UID mismatch, skipping restoration", "namespace", evictedPodInfo.Namespace, "name", evictedPodInfo.Name, "expectedUID", evictedPodInfo.UID, "actualUID", string(pod.UID))
+			continue
+		}
+
+		if err := sandbox.fakeKubeClient.Tracker().Add(pod); err != nil && !apierrors.IsAlreadyExists(err) {
+			return fmt.Errorf("failed to restore pod %s/%s to fake client: %w", evictedPodInfo.Namespace, evictedPodInfo.Name, err)
+		}
+		klog.V(4).InfoS("Successfully restored pod to fake client", "namespace", evictedPodInfo.Namespace, "name", evictedPodInfo.Name, "uid", evictedPodInfo.UID)
+		restoredPods = append(restoredPods, evictedPodInfo)
+	}
+
+	// Second wait loop: Make sure the evicted pods are added back to the fake client.
+	// This ensures the restored pods are accessible through the fake informer's lister.
+	if err := waitForPodsCondition(ctx, restoredPods, func(pod *evictedPodInfo) (bool, error) {
+		podObj, err := sandbox.fakeFactory.Core().V1().Pods().Lister().Pods(pod.Namespace).Get(pod.Name)
+		if err != nil {
+			klog.V(4).InfoS("Pod not yet accessible in fake informer, waiting", "namespace", pod.Namespace, "name", pod.Name)
+			return false, nil
+		}
+		klog.V(4).InfoS("Pod accessible in fake informer", "namespace", pod.Namespace, "name", pod.Name, "node", podObj.Spec.NodeName)
+		return true, nil
+	}, "All restored pods are accessible in fake informer"); err != nil {
+		return fmt.Errorf("timeout waiting for pods to be accessible in fake informer: %w", err)
+	}
+
+	// Third wait loop: Make sure the indexers see the added pods.
+	// This is important to ensure each descheduling cycle can see all the restored pods.
+	// Without this wait, the next cycle might not see the restored pods in the indexer yet.
+	if err := waitForPodsCondition(ctx, restoredPods, func(pod *evictedPodInfo) (bool, error) {
+		exists, err := sandbox.hasObjectInIndexer(v1.SchemeGroupVersion.WithResource("pods"), pod.Namespace, pod.Name)
+		if err != nil {
+			klog.V(4).InfoS("Error checking indexer for restored pod", "namespace", pod.Namespace, "name", pod.Name, "error", err)
+			return false, nil
+		}
+		if !exists {
+			klog.V(4).InfoS("Restored pod not yet in fake indexer, waiting", "namespace", pod.Namespace, "name", pod.Name)
+			return false, nil
+		}
+		klog.V(4).InfoS("Restored pod now in fake indexer", "namespace", pod.Namespace, "name", pod.Name)
+		return true, nil
+	}, "All restored pods are now in fake indexer"); err != nil {
+		return fmt.Errorf("timeout waiting for restored pods to appear in fake indexer: %w", err)
+	}
+
+	return nil
+}
+
 func nodeSelectorFromPolicy(deschedulerPolicy *api.DeschedulerPolicy) (labels.Selector, error) {
 	nodeSelector := labels.Everything()
 	if deschedulerPolicy.NodeSelector != nil {
@@ -246,30 +449,6 @@ func addNodeSelectorIndexer(sharedInformerFactory informers.SharedInformerFactor
 	return nodeutil.AddNodeSelectorIndexer(sharedInformerFactory.Core().V1().Nodes().Informer(), indexerNodeSelectorGlobal, nodeSelector)
 }
 
-func setupInformerIndexers(sharedInformerFactory informers.SharedInformerFactory, deschedulerPolicy *api.DeschedulerPolicy) (podutil.GetPodsAssignedToNodeFunc, error) {
-	// create a new instance of the shared informer factory from the cached client
-	// register the pod informer, otherwise it will not get running
-	getPodsAssignedToNode, err := podutil.BuildGetPodsAssignedToNodeFunc(sharedInformerFactory.Core().V1().Pods().Informer())
-	if err != nil {
-		return nil, fmt.Errorf("build get pods assigned to node function error: %v", err)
-	}
-
-	// TODO(ingvagabund): copy paste all relevant indexers from the real client to the fake one
-	// TODO(ingvagabund): register one indexer per each profile. Respect the precedence of no profile-level node selector is specified.
-	//                    Also, keep a cache of node label selectors to detect duplicates to avoid creating an extra informer.
-
-	nodeSelector, err := nodeSelectorFromPolicy(deschedulerPolicy)
-	if err != nil {
-		return nil, err
-	}
-
-	if err := addNodeSelectorIndexer(sharedInformerFactory, nodeSelector); err != nil {
-		return nil, err
-	}
-
-	return getPodsAssignedToNode, nil
-}
-
 func metricsProviderListToMap(providersList []api.MetricsProvider) map[api.MetricsSource]*api.MetricsProvider {
 	providersMap := make(map[api.MetricsSource]*api.MetricsProvider)
 	for _, provider := range providersList {
@@ -295,15 +474,11 @@ func setupPrometheusProvider(d *descheduler, namespacedSharedInformerFactory inf
 	return nil
 }
 
-func newDescheduler(ctx context.Context, rs *options.DeschedulerServer, deschedulerPolicy *api.DeschedulerPolicy, evictionPolicyGroupVersion string, eventRecorder events.EventRecorder, sharedInformerFactory, namespacedSharedInformerFactory informers.SharedInformerFactory) (*descheduler, error) {
+func newDescheduler(ctx context.Context, rs *options.DeschedulerServer, deschedulerPolicy *api.DeschedulerPolicy, evictionPolicyGroupVersion string, eventRecorder events.EventRecorder, client clientset.Interface, sharedInformerFactory informers.SharedInformerFactory, kubeClientSandbox *kubeClientSandbox) (*descheduler, error) {
 	podInformer := sharedInformerFactory.Core().V1().Pods().Informer()
-
+	// Temporarily register the PVC because it is used by the DefaultEvictor plugin during
-	// Future work could be to let each plugin declare what type of resources it needs; that way dry runs would stay
+	// the descheduling cycle, where informer registration is ignored.
-	// consistent with the real runs without having to keep the list here in sync.
+	_ = sharedInformerFactory.Core().V1().PersistentVolumeClaims().Informer()
-	kubeClientSandbox, err := newDefaultKubeClientSandbox(rs.Client, sharedInformerFactory)
-	if err != nil {
-		return nil, fmt.Errorf("failed to create kube client sandbox: %v", err)
-	}
 
 	getPodsAssignedToNode, err := podutil.BuildGetPodsAssignedToNodeFunc(podInformer)
 	if err != nil {
@@ -312,7 +487,7 @@ func newDescheduler(ctx context.Context, rs *options.DeschedulerServer, deschedu
 
 	podEvictor, err := evictions.NewPodEvictor(
 		ctx,
-		rs.Client,
+		client,
 		eventRecorder,
 		podInformer,
 		rs.DefaultFeatureGates,
@@ -332,6 +507,7 @@ func newDescheduler(ctx context.Context, rs *options.DeschedulerServer, deschedu
 
 	desch := &descheduler{
 		rs:                    rs,
+		client:                client,
 		kubeClientSandbox:     kubeClientSandbox,
 		getPodsAssignedToNode: getPodsAssignedToNode,
 		sharedInformerFactory: sharedInformerFactory,
@@ -479,42 +655,20 @@ func (d *descheduler) runDeschedulerLoop(ctx context.Context) error {
 		metrics.LoopDuration.With(map[string]string{}).Observe(time.Since(loopStartDuration).Seconds())
 	}(time.Now())
 
-	var client clientset.Interface
+	klog.V(3).Infof("Resetting pod evictor counters")
-	// When the dry mode is enable, collect all the relevant objects (mostly pods) under a fake client.
-	// So when evicting pods while running multiple strategies in a row have the cummulative effect
-	// as is when evicting pods for real.
-	if d.rs.DryRun {
-		klog.V(3).Infof("Building a cached client from the cluster for the dry run")
-		// Create a new cache so we start from scratch without any leftovers
-		err := d.kubeClientSandbox.buildSandbox()
-		if err != nil {
-			return err
-		}
-
-		getPodsAssignedToNode, err := setupInformerIndexers(d.kubeClientSandbox.fakeSharedInformerFactory(), d.deschedulerPolicy)
-		if err != nil {
-			return err
-		}
-		d.getPodsAssignedToNode = getPodsAssignedToNode
-
-		fakeCtx, cncl := context.WithCancel(context.TODO())
-		defer cncl()
-		d.kubeClientSandbox.fakeSharedInformerFactory().Start(fakeCtx.Done())
-		d.kubeClientSandbox.fakeSharedInformerFactory().WaitForCacheSync(fakeCtx.Done())
-
-		client = d.kubeClientSandbox.fakeClient()
-		d.sharedInformerFactory = d.kubeClientSandbox.fakeSharedInformerFactory()
-	} else {
-		client = d.rs.Client
-	}
-
-	klog.V(3).Infof("Setting up the pod evictor")
-	d.podEvictor.SetClient(client)
 	d.podEvictor.ResetCounters()
 
-	d.runProfiles(ctx, client)
+	d.runProfiles(ctx, d.client)
 
 	if d.rs.DryRun {
+		if d.kubeClientSandbox == nil {
+			return fmt.Errorf("kubeClientSandbox is nil in DryRun mode")
+		}
+		klog.V(3).Infof("Restoring evicted pods from cache")
+		if err := d.kubeClientSandbox.restoreEvictedPods(ctx); err != nil {
+			klog.ErrorS(err, "Failed to restore evicted pods")
+			return fmt.Errorf("failed to restore evicted pods: %w", err)
+		}
 		d.kubeClientSandbox.reset()
 	}
 
@@ -762,7 +916,8 @@ func RunDeschedulerStrategies(ctx context.Context, rs *options.DeschedulerServer
 		}
 	}
 
-	descheduler, err := newDescheduler(ctx, rs, deschedulerPolicy, evictionPolicyGroupVersion, eventRecorder, sharedInformerFactory, namespacedSharedInformerFactory)
+	// Always create descheduler with real client/factory first to register all informers
+	descheduler, err := newDescheduler(ctx, rs, deschedulerPolicy, evictionPolicyGroupVersion, eventRecorder, rs.Client, sharedInformerFactory, nil)
 	if err != nil {
 		span.AddEvent("Failed to create new descheduler", trace.WithAttributes(attribute.String("err", err.Error())))
 		return err
@@ -776,17 +931,46 @@ func RunDeschedulerStrategies(ctx context.Context, rs *options.DeschedulerServer
 		return err
 	}
 
+	// If in dry run mode, replace the descheduler with one using fake client/factory
+	if rs.DryRun {
+		// Create sandbox with resources to mirror from real client
+		kubeClientSandbox, err := newDefaultKubeClientSandbox(rs.Client, sharedInformerFactory)
+		if err != nil {
+			span.AddEvent("Failed to create kube client sandbox", trace.WithAttributes(attribute.String("err", err.Error())))
+			return fmt.Errorf("failed to create kube client sandbox: %v", err)
+		}
+
+		klog.V(3).Infof("Building a cached client from the cluster for the dry run")
+
+		// TODO(ingvagabund): drop the previous queue
+		// TODO(ingvagabund): stop the previous pod evictor
+		// Replace descheduler with one using fake client/factory
+		descheduler, err = newDescheduler(ctx, rs, deschedulerPolicy, evictionPolicyGroupVersion, eventRecorder, kubeClientSandbox.fakeClient(), kubeClientSandbox.fakeSharedInformerFactory(), kubeClientSandbox)
+		if err != nil {
+			span.AddEvent("Failed to create dry run descheduler", trace.WithAttributes(attribute.String("err", err.Error())))
+			return err
+		}
+	}
+
+	// In dry run mode, start and sync the fake shared informer factory so it can mirror
+	// events from the real factory. Reliable propagation depends on both factories being
+	// fully synced (see WaitForCacheSync calls below), not solely on startup order.
+	if rs.DryRun {
+		descheduler.kubeClientSandbox.fakeSharedInformerFactory().Start(ctx.Done())
+		descheduler.kubeClientSandbox.fakeSharedInformerFactory().WaitForCacheSync(ctx.Done())
+	}
 	sharedInformerFactory.Start(ctx.Done())
 	if metricProviderTokenReconciliation == secretReconciliation {
 		namespacedSharedInformerFactory.Start(ctx.Done())
 	}
 
 	sharedInformerFactory.WaitForCacheSync(ctx.Done())
-	descheduler.podEvictor.WaitForEventHandlersSync(ctx)
 	if metricProviderTokenReconciliation == secretReconciliation {
 		namespacedSharedInformerFactory.WaitForCacheSync(ctx.Done())
 	}
 
+	descheduler.podEvictor.WaitForEventHandlersSync(ctx)
+
 	if descheduler.metricsCollector != nil {
 		go func() {
 			klog.V(2).Infof("Starting metrics collector")

pkg/descheduler/descheduler_test.go

@@ -13,15 +13,18 @@ import (
 	v1 "k8s.io/api/core/v1"
 	policy "k8s.io/api/policy/v1"
 	apierrors "k8s.io/apimachinery/pkg/api/errors"
+	"k8s.io/apimachinery/pkg/api/meta"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/runtime/schema"
+	"k8s.io/apimachinery/pkg/types"
+	"k8s.io/apimachinery/pkg/util/wait"
 	apiversion "k8s.io/apimachinery/pkg/version"
 	fakediscovery "k8s.io/client-go/discovery/fake"
 	"k8s.io/client-go/informers"
-	clientset "k8s.io/client-go/kubernetes"
 	fakeclientset "k8s.io/client-go/kubernetes/fake"
 	core "k8s.io/client-go/testing"
+	"k8s.io/client-go/tools/cache"
 	"k8s.io/component-base/featuregate"
 	"k8s.io/klog/v2"
 	"k8s.io/metrics/pkg/apis/metrics/v1beta1"
@@ -196,20 +199,68 @@ func initDescheduler(t *testing.T, ctx context.Context, featureGates featuregate
 	sharedInformerFactory := informers.NewSharedInformerFactoryWithOptions(rs.Client, 0, informers.WithTransform(trimManagedFields))
 	eventBroadcaster, eventRecorder := utils.GetRecorderAndBroadcaster(ctx, client)
 
-	descheduler, err := newDescheduler(ctx, rs, internalDeschedulerPolicy, "v1", eventRecorder, sharedInformerFactory, nil)
+	// Always create descheduler with real client/factory first to register all informers
+	descheduler, err := newDescheduler(ctx, rs, internalDeschedulerPolicy, "v1", eventRecorder, rs.Client, sharedInformerFactory, nil)
 	if err != nil {
 		eventBroadcaster.Shutdown()
-		t.Fatalf("Unable to create a descheduler instance: %v", err)
+		t.Fatalf("Unable to create descheduler instance: %v", err)
 	}
 
+	// Setup Prometheus provider (only for real client case, not for dry run)
 	if err := setupPrometheusProvider(descheduler, nil); err != nil {
 		eventBroadcaster.Shutdown()
 		t.Fatalf("Failed to setup Prometheus provider: %v", err)
 	}
 
+	// If in dry run mode, replace the descheduler with one using fake client/factory
+	if dryRun {
+		// Create sandbox with resources to mirror from real client
+		kubeClientSandbox, err := newDefaultKubeClientSandbox(rs.Client, sharedInformerFactory)
+		if err != nil {
+			eventBroadcaster.Shutdown()
+			t.Fatalf("Failed to create kube client sandbox: %v", err)
+		}
+
+		// Replace descheduler with one using fake client/factory
+		descheduler, err = newDescheduler(ctx, rs, internalDeschedulerPolicy, "v1", eventRecorder, kubeClientSandbox.fakeClient(), kubeClientSandbox.fakeSharedInformerFactory(), kubeClientSandbox)
+		if err != nil {
+			eventBroadcaster.Shutdown()
+			t.Fatalf("Unable to create dry run descheduler instance: %v", err)
+		}
+	}
+
+	// Start the real shared informer factory after creating the descheduler
+	if dryRun {
+		descheduler.kubeClientSandbox.fakeSharedInformerFactory().Start(ctx.Done())
+		descheduler.kubeClientSandbox.fakeSharedInformerFactory().WaitForCacheSync(ctx.Done())
+	}
 	sharedInformerFactory.Start(ctx.Done())
 	sharedInformerFactory.WaitForCacheSync(ctx.Done())
 
+	if dryRun {
+		if err := wait.PollUntilContextTimeout(ctx, 100*time.Millisecond, 5*time.Second, true, func(ctx context.Context) (bool, error) {
+			for _, obj := range objects {
+				exists, err := descheduler.kubeClientSandbox.hasRuntimeObjectInIndexer(obj)
+				if err != nil {
+					return false, err
+				}
+				metaObj, err := meta.Accessor(obj)
+				if err != nil {
+					return false, fmt.Errorf("failed to get object metadata: %w", err)
+				}
+				key := cache.MetaObjectToName(metaObj).String()
+				if !exists {
+					klog.Infof("Object %q has not propagated to the indexer", key)
+					return false, nil
+				}
+				klog.Infof("Object %q has propagated to the indexer", key)
+			}
+			return true, nil
+		}); err != nil {
+			t.Fatalf("nodes did not propagate to the indexer: %v", err)
+		}
+	}
+
 	return rs, descheduler, client
 }
 
@@ -550,36 +601,12 @@ func TestPodEvictorReset(t *testing.T) {
 	}
 }
 
-// runDeschedulerLoopAndGetEvictedPods is a temporary duplication from runDeschedulerLoop
+// runDeschedulerLoopAndGetEvictedPods runs a descheduling cycle and returns the names of evicted pods.
-// that will be removed after kubeClientSandbox gets migrated to event handlers.
+// This is similar to runDeschedulerLoop but captures evicted pod names before the cache is reset.
 func runDeschedulerLoopAndGetEvictedPods(ctx context.Context, t *testing.T, d *descheduler, dryRun bool) []string {
-	var clientSet clientset.Interface
-	if dryRun {
-		if err := d.kubeClientSandbox.buildSandbox(); err != nil {
-			t.Fatalf("Failed to build sandbox: %v", err)
-		}
-
-		getPodsAssignedToNode, err := setupInformerIndexers(d.kubeClientSandbox.fakeSharedInformerFactory(), d.deschedulerPolicy)
-		if err != nil {
-			t.Fatalf("Failed to setup indexers: %v", err)
-		}
-		d.getPodsAssignedToNode = getPodsAssignedToNode
-
-		fakeCtx, cncl := context.WithCancel(context.TODO())
-		defer cncl()
-		d.kubeClientSandbox.fakeSharedInformerFactory().Start(fakeCtx.Done())
-		d.kubeClientSandbox.fakeSharedInformerFactory().WaitForCacheSync(fakeCtx.Done())
-
-		clientSet = d.kubeClientSandbox.fakeClient()
-		d.sharedInformerFactory = d.kubeClientSandbox.fakeSharedInformerFactory()
-	} else {
-		clientSet = d.rs.Client
-	}
-
-	d.podEvictor.SetClient(clientSet)
 	d.podEvictor.ResetCounters()
 
-	d.runProfiles(ctx, clientSet)
+	d.runProfiles(ctx, d.client)
 
 	var evictedPodNames []string
 	if dryRun {
@@ -587,6 +614,10 @@ func runDeschedulerLoopAndGetEvictedPods(ctx context.Context, t *testing.T, d *d
 		for _, pod := range evictedPodsFromCache {
 			evictedPodNames = append(evictedPodNames, pod.Name)
 		}
+
+		if err := d.kubeClientSandbox.restoreEvictedPods(ctx); err != nil {
+			t.Fatalf("Failed to restore evicted pods: %v", err)
+		}
 		d.kubeClientSandbox.reset()
 	}
 
@@ -962,6 +993,8 @@ func TestNodeLabelSelectorBasedEviction(t *testing.T) {
 			p3 := test.BuildTestPod("p3", 200, 0, node3.Name, updatePod)
 			p4 := test.BuildTestPod("p4", 200, 0, node4.Name, updatePod)
 
+			objects := []runtime.Object{node1, node2, node3, node4, p1, p2, p3, p4}
+
 			// Map pod names to their node names for validation
 			podToNode := map[string]string{
 				"p1": "n1",
@@ -976,7 +1009,7 @@ func TestNodeLabelSelectorBasedEviction(t *testing.T) {
 			}
 
 			ctxCancel, cancel := context.WithCancel(ctx)
-			_, deschedulerInstance, client := initDescheduler(t, ctxCancel, initFeatureGates(), policy, nil, tc.dryRun, node1, node2, node3, node4, p1, p2, p3, p4)
+			_, deschedulerInstance, client := initDescheduler(t, ctxCancel, initFeatureGates(), policy, nil, tc.dryRun, objects...)
 			defer cancel()
 
 			// Verify all pods are created initially
@@ -1008,13 +1041,13 @@ func TestNodeLabelSelectorBasedEviction(t *testing.T) {
 
 			// Verify the correct number of nodes had pods evicted
 			if len(nodesWithEvictedPods) != len(tc.expectedEvictedFromNodes) {
-				t.Errorf("Expected pods to be evicted from %d nodes, got %d nodes: %v", len(tc.expectedEvictedFromNodes), len(nodesWithEvictedPods), nodesWithEvictedPods)
+				t.Fatalf("Expected pods to be evicted from %d nodes, got %d nodes: %v", len(tc.expectedEvictedFromNodes), len(nodesWithEvictedPods), nodesWithEvictedPods)
 			}
 
 			// Verify pods were evicted from the correct nodes
 			for _, nodeName := range tc.expectedEvictedFromNodes {
 				if !nodesWithEvictedPods[nodeName] {
-					t.Errorf("Expected pod to be evicted from node %s, but it was not", nodeName)
+					t.Fatalf("Expected pod to be evicted from node %s, but it was not", nodeName)
 				}
 			}
 
@@ -1028,7 +1061,7 @@ func TestNodeLabelSelectorBasedEviction(t *testing.T) {
 					}
 				}
 				if !found {
-					t.Errorf("Unexpected eviction from node %s", nodeName)
+					t.Fatalf("Unexpected eviction from node %s", nodeName)
 				}
 			}
 
@@ -1141,10 +1174,6 @@ func TestKubeClientSandboxReset(t *testing.T) {
 		t.Fatalf("Failed to create kubeClientSandbox: %v", err)
 	}
 
-	if err := sandbox.buildSandbox(); err != nil {
-		t.Fatalf("Failed to build sandbox: %v", err)
-	}
-
 	eviction1 := &policy.Eviction{
 		ObjectMeta: metav1.ObjectMeta{
 			Name:      p1.Name,
@@ -1158,6 +1187,9 @@ func TestKubeClientSandboxReset(t *testing.T) {
 		},
 	}
 
+	sandbox.fakeSharedInformerFactory().Start(ctx.Done())
+	sandbox.fakeSharedInformerFactory().WaitForCacheSync(ctx.Done())
+
 	if err := sandbox.fakeClient().CoreV1().Pods(p1.Namespace).EvictV1(context.TODO(), eviction1); err != nil {
 		t.Fatalf("Error evicting p1: %v", err)
 	}
@@ -1486,3 +1518,142 @@ func TestPodEvictionReactionFncErrorHandling(t *testing.T) {
 		})
 	}
 }
+
+// verifyPodIdentityFields checks if name, namespace, and UID match expected values
+func verifyPodIdentityFields(t *testing.T, name, namespace, uid, expectedName, expectedNamespace, expectedUID, context string) {
+	t.Helper()
+	if name != expectedName {
+		t.Fatalf("Expected pod name %s%s, got %s", expectedName, context, name)
+	}
+	if namespace != expectedNamespace {
+		t.Fatalf("Expected pod namespace %s%s, got %s", expectedNamespace, context, namespace)
+	}
+	if uid != expectedUID {
+		t.Fatalf("Expected pod UID %s%s, got %s", expectedUID, context, uid)
+	}
+}
+
+// verifyPodIdentity checks if a pod has the expected name, namespace, and UID
+func verifyPodIdentity(t *testing.T, pod *v1.Pod, expectedName, expectedNamespace string, expectedUID types.UID) {
+	t.Helper()
+	verifyPodIdentityFields(t, pod.Name, pod.Namespace, string(pod.UID), expectedName, expectedNamespace, string(expectedUID), "")
+}
+
+func TestEvictedPodRestorationInDryRun(t *testing.T) {
+	// Initialize klog flags
+	// klog.InitFlags(nil)
+
+	// Set verbosity level (higher number = more verbose)
+	// 0 = errors only, 1-4 = info, 5-9 = debug, 10+ = trace
+	// flag.Set("v", "4")
+
+	initPluginRegistry()
+
+	ctx := context.Background()
+	node1 := test.BuildTestNode("n1", 2000, 3000, 10, taintNodeNoSchedule)
+	node2 := test.BuildTestNode("n2", 2000, 3000, 10, nil)
+
+	p1 := test.BuildTestPod("p1", 100, 0, node1.Name, test.SetRSOwnerRef)
+
+	internalDeschedulerPolicy := removePodsViolatingNodeTaintsPolicy()
+	ctxCancel, cancel := context.WithCancel(ctx)
+	defer cancel()
+
+	// Create descheduler with DryRun mode
+	client := fakeclientset.NewSimpleClientset(node1, node2, p1)
+	eventClient := fakeclientset.NewSimpleClientset(node1, node2, p1)
+
+	rs, err := options.NewDeschedulerServer()
+	if err != nil {
+		t.Fatalf("Unable to initialize server: %v", err)
+	}
+	rs.Client = client
+	rs.EventClient = eventClient
+	rs.DefaultFeatureGates = initFeatureGates()
+	rs.DryRun = true // Set DryRun before creating descheduler
+
+	sharedInformerFactory := informers.NewSharedInformerFactoryWithOptions(rs.Client, 0, informers.WithTransform(trimManagedFields))
+	eventBroadcaster, eventRecorder := utils.GetRecorderAndBroadcaster(ctxCancel, client)
+	defer eventBroadcaster.Shutdown()
+
+	// Always create descheduler with real client/factory first to register all informers
+	descheduler, err := newDescheduler(ctxCancel, rs, internalDeschedulerPolicy, "v1", eventRecorder, rs.Client, sharedInformerFactory, nil)
+	if err != nil {
+		t.Fatalf("Unable to create descheduler instance: %v", err)
+	}
+
+	sharedInformerFactory.Start(ctxCancel.Done())
+	sharedInformerFactory.WaitForCacheSync(ctxCancel.Done())
+
+	// Create sandbox with resources to mirror from real client
+	kubeClientSandbox, err := newDefaultKubeClientSandbox(rs.Client, sharedInformerFactory)
+	if err != nil {
+		t.Fatalf("Failed to create kube client sandbox: %v", err)
+	}
+
+	// Replace descheduler with one using fake client/factory
+	descheduler, err = newDescheduler(ctxCancel, rs, internalDeschedulerPolicy, "v1", eventRecorder, kubeClientSandbox.fakeClient(), kubeClientSandbox.fakeSharedInformerFactory(), kubeClientSandbox)
+	if err != nil {
+		t.Fatalf("Unable to create dry run descheduler instance: %v", err)
+	}
+
+	// Start and sync the fake factory after creating the descheduler
+	kubeClientSandbox.fakeSharedInformerFactory().Start(ctxCancel.Done())
+	kubeClientSandbox.fakeSharedInformerFactory().WaitForCacheSync(ctxCancel.Done())
+
+	// Verify the pod exists in the fake client after initialization
+	pod, err := kubeClientSandbox.fakeClient().CoreV1().Pods(p1.Namespace).Get(ctx, p1.Name, metav1.GetOptions{})
+	if err != nil {
+		t.Fatalf("Expected pod %s to exist in fake client after initialization, but got error: %v", p1.Name, err)
+	}
+	verifyPodIdentity(t, pod, p1.Name, p1.Namespace, p1.UID)
+	klog.Infof("Pod %s exists in fake client after initialization", p1.Name)
+
+	// Run two descheduling cycles to verify pod eviction and restoration works repeatedly
+	for i := 1; i <= 2; i++ {
+		// Run descheduling cycle
+		klog.Infof("Running descheduling cycle %d", i)
+		descheduler.podEvictor.ResetCounters()
+		descheduler.runProfiles(ctx, descheduler.client)
+
+		// Verify the pod was evicted (should not exist in fake client anymore)
+		_, err = kubeClientSandbox.fakeClient().CoreV1().Pods(p1.Namespace).Get(ctx, p1.Name, metav1.GetOptions{})
+		if err == nil {
+			t.Fatalf("Expected pod %s to be evicted from fake client in cycle %d, but it still exists", p1.Name, i)
+		}
+		if !apierrors.IsNotFound(err) {
+			t.Fatalf("Expected NotFound error for pod %s in cycle %d, got: %v", p1.Name, i, err)
+		}
+		klog.Infof("Pod %s was successfully evicted from fake client in cycle %d", p1.Name, i)
+
+		// Verify the pod was added to the evicted pods cache
+		evictedPods := descheduler.kubeClientSandbox.evictedPodsCache.list()
+		if len(evictedPods) != 1 {
+			t.Fatalf("Expected 1 pod in evicted cache in cycle %d, got %d", i, len(evictedPods))
+		}
+		verifyPodIdentityFields(t, evictedPods[0].Name, evictedPods[0].Namespace, evictedPods[0].UID, p1.Name, p1.Namespace, string(p1.UID), fmt.Sprintf(" in cycle %d", i))
+		klog.Infof("Pod %s was successfully added to evicted pods cache in cycle %d (UID: %s)", p1.Name, i, p1.UID)
+
+		// Restore evicted pods
+		klog.Infof("Restoring evicted pods from cache in cycle %d", i)
+		if err := descheduler.kubeClientSandbox.restoreEvictedPods(ctx); err != nil {
+			t.Fatalf("Failed to restore evicted pods in cycle %d: %v", i, err)
+		}
+		descheduler.kubeClientSandbox.evictedPodsCache.clear()
+
+		// Verify the pod was restored back to the fake client
+		pod, err = kubeClientSandbox.fakeClient().CoreV1().Pods(p1.Namespace).Get(ctx, p1.Name, metav1.GetOptions{})
+		if err != nil {
+			t.Fatalf("Expected pod %s to be restored to fake client in cycle %d, but got error: %v", p1.Name, i, err)
+		}
+		verifyPodIdentity(t, pod, p1.Name, p1.Namespace, p1.UID)
+		klog.Infof("Pod %s was successfully restored to fake client in cycle %d (UID: %s)", p1.Name, i, pod.UID)
+
+		// Verify cache was cleared after restoration
+		evictedPods = descheduler.kubeClientSandbox.evictedPodsCache.list()
+		if len(evictedPods) != 0 {
+			t.Fatalf("Expected evicted cache to be empty after restoration in cycle %d, got %d pods", i, len(evictedPods))
+		}
+		klog.Infof("Evicted pods cache was cleared after restoration in cycle %d", i)
+	}
+}

pkg/descheduler/evictions/evictions.go

@@ -403,12 +403,6 @@ func (pe *PodEvictor) ResetCounters() {
 	pe.totalPodCount = 0
 }
 
-func (pe *PodEvictor) SetClient(client clientset.Interface) {
-	pe.mu.Lock()
-	defer pe.mu.Unlock()
-	pe.client = client
-}
-
 func (pe *PodEvictor) evictionRequestsTotal() uint {
 	if pe.featureGates.Enabled(features.EvictionsInBackground) {
 		return pe.erCache.evictionRequestsTotal()

test/test_utils.go

@@ -43,6 +43,10 @@ import (
 // BuildTestPod creates a test pod with given parameters.
 func BuildTestPod(name string, cpu, memory int64, nodeName string, apply func(*v1.Pod)) *v1.Pod {
 	pod := &v1.Pod{
+		TypeMeta: metav1.TypeMeta{
+			APIVersion: "v1",
+			Kind:       "Pod",
+		},
 		ObjectMeta: metav1.ObjectMeta{
 			Namespace: "default",
 			Name:      name,
@@ -76,6 +80,10 @@ func BuildTestPod(name string, cpu, memory int64, nodeName string, apply func(*v
 func BuildTestPDB(name, appLabel string) *policyv1.PodDisruptionBudget {
 	maxUnavailable := intstr.FromInt32(1)
 	pdb := &policyv1.PodDisruptionBudget{
+		TypeMeta: metav1.TypeMeta{
+			APIVersion: "policy/v1",
+			Kind:       "PodDisruptionBudget",
+		},
 		ObjectMeta: metav1.ObjectMeta{
 			Namespace: "default",
 			Name:      name,
@@ -94,6 +102,10 @@ func BuildTestPDB(name, appLabel string) *policyv1.PodDisruptionBudget {
 
 func BuildTestPVC(name, storageClass string) *v1.PersistentVolumeClaim {
 	pvc := &v1.PersistentVolumeClaim{
+		TypeMeta: metav1.TypeMeta{
+			APIVersion: "v1",
+			Kind:       "PersistentVolumeClaim",
+		},
 		ObjectMeta: metav1.ObjectMeta{
 			Namespace: "default",
 			Name:      name,
@@ -114,6 +126,10 @@ func BuildTestPVC(name, storageClass string) *v1.PersistentVolumeClaim {
 // BuildPodMetrics creates a test podmetrics with given parameters.
 func BuildPodMetrics(name string, millicpu, mem int64) *v1beta1.PodMetrics {
 	return &v1beta1.PodMetrics{
+		TypeMeta: metav1.TypeMeta{
+			APIVersion: "metrics.k8s.io/v1beta1",
+			Kind:       "PodMetrics",
+		},
 		ObjectMeta: metav1.ObjectMeta{
 			Name:      name,
 			Namespace: "default",
@@ -171,6 +187,10 @@ func GetDaemonSetOwnerRefList() []metav1.OwnerReference {
 // BuildTestNode creates a node with specified capacity.
 func BuildTestNode(name string, millicpu, mem, pods int64, apply func(*v1.Node)) *v1.Node {
 	node := &v1.Node{
+		TypeMeta: metav1.TypeMeta{
+			APIVersion: "v1",
+			Kind:       "Node",
+		},
 		ObjectMeta: metav1.ObjectMeta{
 			Name:     name,
 			SelfLink: fmt.Sprintf("/api/v1/nodes/%s", name),
@@ -201,6 +221,10 @@ func BuildTestNode(name string, millicpu, mem, pods int64, apply func(*v1.Node))
 
 func BuildNodeMetrics(name string, millicpu, mem int64) *v1beta1.NodeMetrics {
 	return &v1beta1.NodeMetrics{
+		TypeMeta: metav1.TypeMeta{
+			APIVersion: "metrics.k8s.io/v1beta1",
+			Kind:       "NodeMetrics",
+		},
 		ObjectMeta: metav1.ObjectMeta{
 			Name: name,
 		},