Make sure dry runs sees all the resources a normal run would do (#1526)

* generic resource handling, so that dry run has all the expected resource types and objects

* simpler code and better names

* fix imports

pkg/descheduler/descheduler.go

@@ -23,6 +23,9 @@ import (
 	"strconv"
 	"time"
 
+	schedulingv1 "k8s.io/api/scheduling/v1"
+	"k8s.io/apimachinery/pkg/runtime/schema"
+
 	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/trace"
 	"k8s.io/apimachinery/pkg/api/meta"
@@ -34,15 +37,12 @@ import (
 
 	v1 "k8s.io/api/core/v1"
 	policy "k8s.io/api/policy/v1"
-	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/labels"
 	"k8s.io/apimachinery/pkg/runtime"
 	utilversion "k8s.io/apimachinery/pkg/util/version"
 	"k8s.io/apimachinery/pkg/util/wait"
 	clientset "k8s.io/client-go/kubernetes"
 	fakeclientset "k8s.io/client-go/kubernetes/fake"
-	listersv1 "k8s.io/client-go/listers/core/v1"
-	schedulingv1 "k8s.io/client-go/listers/scheduling/v1"
 	core "k8s.io/client-go/testing"
 
 	"sigs.k8s.io/descheduler/pkg/descheduler/client"
@@ -71,10 +71,7 @@ type profileRunner struct {
 
 type descheduler struct {
 	rs                     *options.DeschedulerServer
-	podLister              listersv1.PodLister
-	nodeLister             listersv1.NodeLister
-	namespaceLister        listersv1.NamespaceLister
-	priorityClassLister    schedulingv1.PriorityClassLister
+	ir                     *informerResources
 	getPodsAssignedToNode  podutil.GetPodsAssignedToNodeFunc
 	sharedInformerFactory  informers.SharedInformerFactory
 	deschedulerPolicy      *api.DeschedulerPolicy
@@ -83,12 +80,60 @@ type descheduler struct {
 	podEvictionReactionFnc func(*fakeclientset.Clientset) func(action core.Action) (bool, runtime.Object, error)
 }
 
+type informerResources struct {
+	sharedInformerFactory informers.SharedInformerFactory
+	resourceToInformer    map[schema.GroupVersionResource]informers.GenericInformer
+}
+
+func newInformerResources(sharedInformerFactory informers.SharedInformerFactory) *informerResources {
+	return &informerResources{
+		sharedInformerFactory: sharedInformerFactory,
+		resourceToInformer:    make(map[schema.GroupVersionResource]informers.GenericInformer),
+	}
+}
+
+func (ir *informerResources) Uses(resources ...schema.GroupVersionResource) error {
+	for _, resource := range resources {
+		informer, err := ir.sharedInformerFactory.ForResource(resource)
+		if err != nil {
+			return err
+		}
+
+		ir.resourceToInformer[resource] = informer
+	}
+	return nil
+}
+
+// CopyTo Copy informer subscriptions to the new factory and objects to the fake client so that the backing caches are populated for when listers are used.
+func (ir *informerResources) CopyTo(fakeClient *fakeclientset.Clientset, newFactory informers.SharedInformerFactory) error {
+	for resource, informer := range ir.resourceToInformer {
+		_, err := newFactory.ForResource(resource)
+		if err != nil {
+			return fmt.Errorf("error getting resource %s: %w", resource, err)
+		}
+
+		objects, err := informer.Lister().List(labels.Everything())
+		if err != nil {
+			return fmt.Errorf("error listing %s: %w", informer, err)
+		}
+
+		for _, object := range objects {
+			fakeClient.Tracker().Add(object)
+		}
+	}
+	return nil
+}
+
 func newDescheduler(rs *options.DeschedulerServer, deschedulerPolicy *api.DeschedulerPolicy, evictionPolicyGroupVersion string, eventRecorder events.EventRecorder, sharedInformerFactory informers.SharedInformerFactory) (*descheduler, error) {
 	podInformer := sharedInformerFactory.Core().V1().Pods().Informer()
-	podLister := sharedInformerFactory.Core().V1().Pods().Lister()
-	nodeLister := sharedInformerFactory.Core().V1().Nodes().Lister()
-	namespaceLister := sharedInformerFactory.Core().V1().Namespaces().Lister()
-	priorityClassLister := sharedInformerFactory.Scheduling().V1().PriorityClasses().Lister()
+
+	ir := newInformerResources(sharedInformerFactory)
+	ir.Uses(v1.SchemeGroupVersion.WithResource("pods"),
+		v1.SchemeGroupVersion.WithResource("nodes"),
+		// Future work could be to let each plugin declare what type of resources it needs; that way dry runs would stay
+		// consistent with the real runs without having to keep the list here in sync.
+		v1.SchemeGroupVersion.WithResource("namespaces"),                // Used by the defaultevictor plugin
+		schedulingv1.SchemeGroupVersion.WithResource("priorityclasses")) // Used by the defaultevictor plugin
 
 	getPodsAssignedToNode, err := podutil.BuildGetPodsAssignedToNodeFunc(podInformer)
 	if err != nil {
@@ -109,10 +154,7 @@ func newDescheduler(rs *options.DeschedulerServer, deschedulerPolicy *api.Desche
 
 	return &descheduler{
 		rs:                     rs,
-		podLister:              podLister,
-		nodeLister:             nodeLister,
-		namespaceLister:        namespaceLister,
-		priorityClassLister:    priorityClassLister,
+		ir:                     ir,
 		getPodsAssignedToNode:  getPodsAssignedToNode,
 		sharedInformerFactory:  sharedInformerFactory,
 		deschedulerPolicy:      deschedulerPolicy,
@@ -146,13 +188,14 @@ func (d *descheduler) runDeschedulerLoop(ctx context.Context, nodes []*v1.Node)
 		fakeClient := fakeclientset.NewSimpleClientset()
 		// simulate a pod eviction by deleting a pod
 		fakeClient.PrependReactor("create", "pods", d.podEvictionReactionFnc(fakeClient))
-		err := cachedClient(d.rs.Client, fakeClient, d.podLister, d.nodeLister, d.namespaceLister, d.priorityClassLister)
+		fakeSharedInformerFactory := informers.NewSharedInformerFactory(fakeClient, 0)
+
+		err := d.ir.CopyTo(fakeClient, fakeSharedInformerFactory)
 		if err != nil {
 			return err
 		}
 
 		// create a new instance of the shared informer factor from the cached client
-		fakeSharedInformerFactory := informers.NewSharedInformerFactory(fakeClient, 0)
 		// register the pod informer, otherwise it will not get running
 		d.getPodsAssignedToNode, err = podutil.BuildGetPodsAssignedToNodeFunc(fakeSharedInformerFactory.Core().V1().Pods().Informer())
 		if err != nil {
@@ -336,62 +379,6 @@ func podEvictionReactionFnc(fakeClient *fakeclientset.Clientset) func(action cor
 	}
 }
 
-func cachedClient(
-	realClient clientset.Interface,
-	fakeClient *fakeclientset.Clientset,
-	podLister listersv1.PodLister,
-	nodeLister listersv1.NodeLister,
-	namespaceLister listersv1.NamespaceLister,
-	priorityClassLister schedulingv1.PriorityClassLister,
-) error {
-	klog.V(3).Infof("Pulling resources for the cached client from the cluster")
-	pods, err := podLister.List(labels.Everything())
-	if err != nil {
-		return fmt.Errorf("unable to list pods: %v", err)
-	}
-
-	for _, item := range pods {
-		if _, err := fakeClient.CoreV1().Pods(item.Namespace).Create(context.TODO(), item, metav1.CreateOptions{}); err != nil {
-			return fmt.Errorf("unable to copy pod: %v", err)
-		}
-	}
-
-	nodes, err := nodeLister.List(labels.Everything())
-	if err != nil {
-		return fmt.Errorf("unable to list nodes: %v", err)
-	}
-
-	for _, item := range nodes {
-		if _, err := fakeClient.CoreV1().Nodes().Create(context.TODO(), item, metav1.CreateOptions{}); err != nil {
-			return fmt.Errorf("unable to copy node: %v", err)
-		}
-	}
-
-	namespaces, err := namespaceLister.List(labels.Everything())
-	if err != nil {
-		return fmt.Errorf("unable to list namespaces: %v", err)
-	}
-
-	for _, item := range namespaces {
-		if _, err := fakeClient.CoreV1().Namespaces().Create(context.TODO(), item, metav1.CreateOptions{}); err != nil {
-			return fmt.Errorf("unable to copy namespace: %v", err)
-		}
-	}
-
-	priorityClasses, err := priorityClassLister.List(labels.Everything())
-	if err != nil {
-		return fmt.Errorf("unable to list priorityclasses: %v", err)
-	}
-
-	for _, item := range priorityClasses {
-		if _, err := fakeClient.SchedulingV1().PriorityClasses().Create(context.TODO(), item, metav1.CreateOptions{}); err != nil {
-			return fmt.Errorf("unable to copy priorityclass: %v", err)
-		}
-	}
-
-	return nil
-}
-
 func RunDeschedulerStrategies(ctx context.Context, rs *options.DeschedulerServer, deschedulerPolicy *api.DeschedulerPolicy, evictionPolicyGroupVersion string) error {
 	var span trace.Span
 	ctx, span = tracing.Tracer().Start(ctx, "RunDeschedulerStrategies")
@@ -428,7 +415,8 @@ func RunDeschedulerStrategies(ctx context.Context, rs *options.DeschedulerServer
 		// A next context is created here intentionally to avoid nesting the spans via context.
 		sCtx, sSpan := tracing.Tracer().Start(ctx, "NonSlidingUntil")
 		defer sSpan.End()
-		nodes, err := nodeutil.ReadyNodes(sCtx, rs.Client, descheduler.nodeLister, nodeSelector)
+
+		nodes, err := nodeutil.ReadyNodes(sCtx, rs.Client, descheduler.sharedInformerFactory.Core().V1().Nodes().Lister(), nodeSelector)
 		if err != nil {
 			sSpan.AddEvent("Failed to detect ready nodes", trace.WithAttributes(attribute.String("err", err.Error())))
 			klog.Error(err)