resourcequota: use singleflight.Group to reduce apiserver load

relates to #22422 and #123806

staging/src/k8s.io/apiserver/pkg/admission/plugin/resourcequota/resource_access.go

@@ -21,6 +21,7 @@ import (
 	"fmt"
 	"time"
 
+	"golang.org/x/sync/singleflight"
 	corev1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/labels"
@@ -51,6 +52,7 @@ type quotaAccessor struct {
 	// This lets us handle the case of latent caches, by looking up actual results for a namespace on cache miss/no results.
 	// We track the lookup result here so that for repeated requests, we don't look it up very often.
 	liveLookupCache *lru.Cache
+	group           singleflight.Group
 	liveTTL         time.Duration
 	// updatedQuotas holds a cache of quotas that we've updated.  This is used to pull the "really latest" during back to
 	// back quota evaluations that touch the same quota doc.  This only works because we can compare etcd resourceVersions
@@ -114,11 +116,9 @@ func (e *quotaAccessor) GetQuotas(namespace string) ([]corev1.ResourceQuota, err
 	if len(items) == 0 {
 		lruItemObj, ok := e.liveLookupCache.Get(namespace)
 		if !ok || lruItemObj.(liveLookupEntry).expiry.Before(time.Now()) {
-			// TODO: If there are multiple operations at the same time and cache has just expired,
-			// this may cause multiple List operations being issued at the same time.
-			// If there is already in-flight List() for a given namespace, we should wait until
-			// it is finished and cache is updated instead of doing the same, also to avoid
-			// throttling - see #22422 for details.
+			// use singleflight.Group to avoid flooding the apiserver with repeated
+			// requests. See #22422 for details.
+			lruItemObj, err, _ = e.group.Do(namespace, func() (interface{}, error) {
 				liveList, err := e.client.CoreV1().ResourceQuotas(namespace).List(context.TODO(), metav1.ListOptions{})
 				if err != nil {
 					return nil, err
@@ -128,7 +128,11 @@ func (e *quotaAccessor) GetQuotas(namespace string) ([]corev1.ResourceQuota, err
 					newEntry.items = append(newEntry.items, &liveList.Items[i])
 				}
 				e.liveLookupCache.Add(namespace, newEntry)
-			lruItemObj = newEntry
+				return newEntry, nil
+			})
+			if err != nil {
+				return nil, err
+			}
 		}
 		lruEntry := lruItemObj.(liveLookupEntry)
 		for i := range lruEntry.items {

staging/src/k8s.io/apiserver/pkg/admission/plugin/resourcequota/resource_access_test.go

@@ -17,7 +17,10 @@ limitations under the License.
 package resourcequota
 
 import (
+	"fmt"
 	"reflect"
+	"sync"
+	"sync/atomic"
 	"testing"
 	"time"
 
@@ -27,6 +30,7 @@ import (
 	corev1 "k8s.io/api/core/v1"
 	"k8s.io/client-go/informers"
 	"k8s.io/client-go/kubernetes/fake"
+	core "k8s.io/client-go/testing"
 	"k8s.io/utils/lru"
 )
 
@@ -121,5 +125,122 @@ func TestLRUCacheLookup(t *testing.T) {
 			}
 		})
 	}
-
+}
+
+// TestGetQuotas ensures we do not have multiple LIST calls to the apiserver
+// in-flight at any one time. This is to ensure the issue described in #22422 do
+// not happen again.
+func TestGetQuotas(t *testing.T) {
+	var (
+		testNamespace1              = "test-a"
+		testNamespace2              = "test-b"
+		listCallCountTestNamespace1 int64
+		listCallCountTestNamespace2 int64
+	)
+	resourceQuota := &corev1.ResourceQuota{
+		ObjectMeta: metav1.ObjectMeta{
+			Name: "foo",
+		},
+	}
+
+	resourceQuotas := []*corev1.ResourceQuota{resourceQuota}
+
+	kubeClient := &fake.Clientset{}
+	informerFactory := informers.NewSharedInformerFactory(kubeClient, 0)
+
+	accessor, _ := newQuotaAccessor()
+	accessor.client = kubeClient
+	accessor.lister = informerFactory.Core().V1().ResourceQuotas().Lister()
+
+	kubeClient.AddReactor("list", "resourcequotas", func(action core.Action) (bool, runtime.Object, error) {
+		switch action.GetNamespace() {
+		case testNamespace1:
+			atomic.AddInt64(&listCallCountTestNamespace1, 1)
+		case testNamespace2:
+			atomic.AddInt64(&listCallCountTestNamespace2, 1)
+		default:
+			t.Error("unexpected namespace")
+		}
+
+		resourceQuotaList := &corev1.ResourceQuotaList{
+			ListMeta: metav1.ListMeta{
+				ResourceVersion: fmt.Sprintf("%d", len(resourceQuotas)),
+			},
+		}
+		for i, quota := range resourceQuotas {
+			quota.ResourceVersion = fmt.Sprintf("%d", i)
+			quota.Namespace = action.GetNamespace()
+			resourceQuotaList.Items = append(resourceQuotaList.Items, *quota)
+		}
+		// make the handler slow so concurrent calls exercise the singleflight
+		time.Sleep(time.Second)
+		return true, resourceQuotaList, nil
+	})
+
+	wg := sync.WaitGroup{}
+	for i := 0; i < 10; i++ {
+		wg.Add(2)
+		// simulating concurrent calls after a cache failure
+		go func() {
+			defer wg.Done()
+			quotas, err := accessor.GetQuotas(testNamespace1)
+			if err != nil {
+				t.Errorf("unexpected error: %v", err)
+			}
+			if len(quotas) != len(resourceQuotas) {
+				t.Errorf("Expected %d resource quotas, got %d", len(resourceQuotas), len(quotas))
+			}
+			for _, q := range quotas {
+				if q.Namespace != testNamespace1 {
+					t.Errorf("Expected %s namespace, got %s", testNamespace1, q.Namespace)
+				}
+			}
+		}()
+
+		// simulation of different namespaces is a call for a different group key, but not shared with the first namespace
+		go func() {
+			defer wg.Done()
+			quotas, err := accessor.GetQuotas(testNamespace2)
+			if err != nil {
+				t.Errorf("unexpected error: %v", err)
+			}
+			if len(quotas) != len(resourceQuotas) {
+				t.Errorf("Expected %d resource quotas, got %d", len(resourceQuotas), len(quotas))
+			}
+			for _, q := range quotas {
+				if q.Namespace != testNamespace2 {
+					t.Errorf("Expected %s namespace, got %s", testNamespace2, q.Namespace)
+				}
+			}
+		}()
+	}
+
+	// and here we wait for all the goroutines
+	wg.Wait()
+	// since all the calls with the same namespace will be held, they must
+	// be caught on the singleflight group. there are two different sets of
+	// namespace calls hence only 2.
+	if listCallCountTestNamespace1 != 1 {
+		t.Errorf("Expected 1 resource quota call, got %d", listCallCountTestNamespace1)
+	}
+	if listCallCountTestNamespace2 != 1 {
+		t.Errorf("Expected 1 resource quota call, got %d", listCallCountTestNamespace2)
+	}
+
+	// invalidate the cache
+	accessor.liveLookupCache.Remove(testNamespace1)
+	quotas, err := accessor.GetQuotas(testNamespace1)
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	if len(quotas) != len(resourceQuotas) {
+		t.Errorf("Expected %d resource quotas, got %d", len(resourceQuotas), len(quotas))
+	}
+
+	if listCallCountTestNamespace1 != 2 {
+		t.Errorf("Expected 2 resource quota call, got %d", listCallCountTestNamespace1)
+	}
+	if listCallCountTestNamespace2 != 1 {
+		t.Errorf("Expected 1 resource quota call, got %d", listCallCountTestNamespace2)
+	}
 }