Fix -Consistent paginated lists serve from cache

staging/src/k8s.io/apiserver/pkg/storage/cacher/cacher_whitebox_test.go

@@ -662,6 +662,7 @@ func TestMatchExactResourceVersionFallback(t *testing.T) {
 	}
 	for _, tc := range tcs {
 		t.Run(tc.name, func(t *testing.T) {
+			featuregatetesting.SetFeatureGateDuringTest(t, utilfeature.DefaultFeatureGate, features.ListFromCacheSnapshot, true)
 			backingStorage := &dummyStorage{}
 			expectStoreRequests := 0
 			backingStorage.getListFn = func(_ context.Context, key string, opts storage.ListOptions, listObj runtime.Object) error {
@@ -759,6 +760,125 @@ func TestGetListNonRecursiveCacheBypass(t *testing.T) {
 	}
 }
 
+func TestGetListNonRecursiveCacheWithConsistentListFromCache(t *testing.T) {
+	// Set feature gates once at the beginning since we only care about ConsistentListFromCache=true and ListFromCacheSnapshot=false
+	featuregatetesting.SetFeatureGateDuringTest(t, utilfeature.DefaultFeatureGate, features.ConsistentListFromCache, true)
+	featuregatetesting.SetFeatureGateDuringTest(t, utilfeature.DefaultFeatureGate, features.ListFromCacheSnapshot, false)
+	forceRequestWatchProgressSupport(t)
+
+	tests := []struct {
+		name                    string
+		consistentListFromCache bool
+		expectGetListCallCount  int
+		expectGetCurrentRV      bool
+		injectRVError           bool
+		expectedError           error
+	}{
+		{
+			name:                    "ConsistentListFromCache enabled - served from cache",
+			consistentListFromCache: true,
+			expectGetListCallCount:  1,
+			expectGetCurrentRV:      true,
+			injectRVError:           false,
+			expectedError:           nil,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			var getListCount, getCurrentRVCount int
+			backingStorage := &dummyStorage{}
+
+			backingStorage.getListFn = func(ctx context.Context, key string, opts storage.ListOptions, listObj runtime.Object) error {
+				getListCount++
+				if tc.injectRVError {
+					return errDummy
+				}
+				podList := listObj.(*example.PodList)
+				podList.ListMeta = metav1.ListMeta{ResourceVersion: "100"}
+				return nil
+			}
+
+			backingStorage.getRVFn = func(ctx context.Context) (uint64, error) {
+				getCurrentRVCount++
+				rv := uint64(100)
+				err := error(nil)
+				if tc.injectRVError {
+					err = errDummy
+					return 0, err
+				}
+				return rv, nil
+			}
+
+			cacher, v, err := newTestCacher(backingStorage)
+			if err != nil {
+				t.Fatalf("Couldn't create cacher: %v", err)
+			}
+			defer cacher.Stop()
+
+			// Wait for cacher to be ready before injecting errors
+			if err := cacher.ready.wait(context.Background()); err != nil {
+				t.Fatalf("unexpected error waiting for the cache to be ready: %v", err)
+			}
+			delegator := NewCacheDelegator(cacher, backingStorage)
+			defer delegator.Stop()
+
+			// Setup test object
+			key := "pods/ns"
+			input := &example.Pod{ObjectMeta: metav1.ObjectMeta{Name: "foo", Namespace: "ns"}}
+			if err := v.UpdateObject(input, 100); err != nil {
+				t.Fatalf("Unexpected error: %v", err)
+			}
+
+			// Put object into the store
+			if err := cacher.watchCache.Add(input); err != nil {
+				t.Fatalf("Unexpected error: %v", err)
+			}
+
+			pred := storage.SelectionPredicate{
+				Label: labels.Everything(),
+				Field: fields.Everything(),
+				Limit: 500,
+			}
+			result := &example.PodList{}
+
+			// Make the list call with empty RV - delegator will get current RV and use it
+			err = delegator.GetList(context.TODO(), key, storage.ListOptions{
+				ResourceVersion: "",
+				Predicate:       pred,
+				Recursive:       true,
+			}, result)
+
+			// Verify error matches expectation
+			if !errors.Is(err, tc.expectedError) {
+				t.Errorf("Expected error %v, got: %v", tc.expectedError, err)
+			}
+
+			// Verify the correct storage method was called
+			if getListCount != tc.expectGetListCallCount {
+				t.Errorf("Expected GetList to be called %d times, but it was called %d times", tc.expectGetListCallCount, getListCount)
+			}
+			if tc.expectGetCurrentRV && getCurrentRVCount == 0 {
+				t.Error("Expected GetCurrentResourceVersion to be called, but it wasn't")
+			}
+			if !tc.expectGetCurrentRV && getCurrentRVCount > 0 {
+				t.Errorf("Expected GetCurrentResourceVersion not to be called, but it was called %d times", getCurrentRVCount)
+			}
+
+			// For successful cache reads, verify the resource version
+			if err == nil {
+				resultRV, err := cacher.versioner.ParseResourceVersion(result.ResourceVersion)
+				if err != nil {
+					t.Fatalf("Failed to parse result resource version: %v", err)
+				}
+				expectedRV := uint64(100)
+				if resultRV != expectedRV {
+					t.Errorf("Expected RV %d but got %d", expectedRV, resultRV)
+				}
+			}
+		})
+	}
+}
 func TestGetCacheBypass(t *testing.T) {
 	backingStorage := &dummyStorage{}
 	cacher, _, err := newTestCacher(backingStorage)

staging/src/k8s.io/apiserver/pkg/storage/cacher/delegator.go

@@ -206,6 +206,7 @@ func (c *CacheDelegator) GetList(ctx context.Context, key string, opts storage.L
 			return c.storage.GetList(ctx, key, opts, listObj)
 		}
 	}
+	fallbackOpts := opts
 	if result.ConsistentRead {
 		listRV, err = c.storage.GetCurrentResourceVersion(ctx)
 		if err != nil {
@@ -213,20 +214,28 @@ func (c *CacheDelegator) GetList(ctx context.Context, key string, opts storage.L
 		}
 		// Setting resource version for consistent read in cache based on current ResourceVersion in etcd.
 		opts.ResourceVersion = strconv.FormatInt(int64(listRV), 10)
+		// If continue is not set, we need to set the resource version match to ResourceVersionMatchNotOlderThan to serve latest from cache
+		if opts.Predicate.Continue == "" {
+			opts.ResourceVersionMatch = metav1.ResourceVersionMatchNotOlderThan
+		}
 	}
 	err = c.cacher.GetList(ctx, key, opts, listObj)
 	success := "true"
 	fallback := "false"
 	if err != nil {
-		if errors.IsResourceExpired(err) {
-			return c.storage.GetList(ctx, key, opts, listObj)
+		// ResourceExpired error occurs when attempting to list from cache with a specific resourceVersion
+		// that is no longer available in the cache. With ListFromCacheSnapshot feature (1.34+), we can
+		// serve exact resourceVersion requests from cache if available, falling back to storage only when
+		// the requested version is expired.
+		if errors.IsResourceExpired(err) && utilfeature.DefaultFeatureGate.Enabled(features.ListFromCacheSnapshot) {
+			return c.storage.GetList(ctx, key, fallbackOpts, listObj)
 		}
 		if result.ConsistentRead {
+			// IsTooLargeResourceVersion occurs when the requested RV is higher than cache's current RV
+			// and cache hasn't caught up within the timeout period. Fall back to etcd.
 			if storage.IsTooLargeResourceVersion(err) {
 				fallback = "true"
-				// Reset resourceVersion during fallback from consistent read.
-				opts.ResourceVersion = ""
-				err = c.storage.GetList(ctx, key, opts, listObj)
+				err = c.storage.GetList(ctx, key, fallbackOpts, listObj)
 			}
 			if err != nil {
 				success = "false"