discovery: kubernetes: Avoid creating unnecessary Kubernetes indexers in RoleEndpointSlice

This was due to a missing "return", see https://github.com/prometheus/prometheus/pull/13554#discussion_r1490965817

Signed-off-by: machine424 <ayoubmrini424@gmail.com>

discovery/kubernetes/endpointslice_test.go

@@ -18,6 +18,7 @@ import (
 	"testing"
 
 	"github.com/prometheus/common/model"
+	"github.com/stretchr/testify/require"
 	corev1 "k8s.io/api/core/v1"
 	v1 "k8s.io/api/discovery/v1"
 	"k8s.io/api/discovery/v1beta1"
@@ -1405,3 +1406,41 @@ func TestEndpointSliceDiscoveryEmptyPodStatus(t *testing.T) {
 		expectedRes:      map[string]*targetgroup.Group{},
 	}.Run(t)
 }
+
+// TestEndpointSliceInfIndexersCount makes sure that RoleEndpointSlice discovery
+// sets up indexing for the main Kube informer only when needed.
+// See: https://github.com/prometheus/prometheus/pull/13554#discussion_r1490965817
+func TestEndpointSliceInfIndexersCount(t *testing.T) {
+	tests := []struct {
+		name             string
+		withNodeMetadata bool
+	}{
+		{"with node metadata", true},
+		{"without node metadata", false},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			var (
+				n                    *Discovery
+				mainInfIndexersCount int
+			)
+			if tc.withNodeMetadata {
+				mainInfIndexersCount = 1
+				n, _ = makeDiscoveryWithMetadata(RoleEndpointSlice, NamespaceDiscovery{}, AttachMetadataConfig{Node: true})
+			} else {
+				n, _ = makeDiscovery(RoleEndpointSlice, NamespaceDiscovery{})
+			}
+
+			k8sDiscoveryTest{
+				discovery: n,
+				afterStart: func() {
+					n.RLock()
+					defer n.RUnlock()
+					require.Len(t, n.discoverers, 1)
+					require.Len(t, n.discoverers[0].(*EndpointSlice).endpointSliceInf.GetIndexer().GetIndexers(), mainInfIndexersCount)
+				},
+			}.Run(t)
+		})
+	}
+}

discovery/kubernetes/kubernetes.go

@@ -815,7 +815,7 @@ func (d *Discovery) newEndpointsByNodeInformer(plw *cache.ListWatch) cache.Share
 func (d *Discovery) newEndpointSlicesByNodeInformer(plw *cache.ListWatch, object runtime.Object) cache.SharedIndexInformer {
 	indexers := make(map[string]cache.IndexFunc)
 	if !d.attachMetadata.Node {
-		cache.NewSharedIndexInformer(plw, &disv1.EndpointSlice{}, resyncDisabled, indexers)
+		return cache.NewSharedIndexInformer(plw, object, resyncDisabled, indexers)
 	}
 
 	indexers[nodeIndex] = func(obj interface{}) ([]string, error) {

discovery/kubernetes/kubernetes_test.go

@@ -128,7 +128,7 @@ func (d k8sDiscoveryTest) Run(t *testing.T) {
 	}
 
 	resChan := make(chan map[string]*targetgroup.Group)
-	go readResultWithTimeout(t, ch, d.expectedMaxItems, time.Second, resChan)
+	go readResultWithTimeout(t, ctx, ch, d.expectedMaxItems, time.Second, resChan)
 
 	dd, ok := d.discovery.(hasSynced)
 	require.True(t, ok, "discoverer does not implement hasSynced interface")
@@ -141,13 +141,18 @@ func (d k8sDiscoveryTest) Run(t *testing.T) {
 	if d.expectedRes != nil {
 		res := <-resChan
 		requireTargetGroups(t, d.expectedRes, res)
+	} else {
+		// Stop readResultWithTimeout and wait for it.
+		cancel()
+		<-resChan
 	}
 }
 
 // readResultWithTimeout reads all targetgroups from channel with timeout.
 // It merges targetgroups by source and sends the result to result channel.
-func readResultWithTimeout(t *testing.T, ch <-chan []*targetgroup.Group, max int, timeout time.Duration, resChan chan<- map[string]*targetgroup.Group) {
+func readResultWithTimeout(t *testing.T, ctx context.Context, ch <-chan []*targetgroup.Group, max int, stopAfter time.Duration, resChan chan<- map[string]*targetgroup.Group) {
 	res := make(map[string]*targetgroup.Group)
+	timeout := time.After(stopAfter)
 Loop:
 	for {
 		select {
@@ -162,12 +167,15 @@ Loop:
 				// Reached max target groups we may get, break fast.
 				break Loop
 			}
-		case <-time.After(timeout):
+		case <-timeout:
 			// Because we use queue, an object that is created then
 			// deleted or updated may be processed only once.
 			// So possibly we may skip events, timed out here.
 			t.Logf("timed out, got %d (max: %d) items, some events are skipped", len(res), max)
 			break Loop
+		case <-ctx.Done():
+			t.Logf("stopped, got %d (max: %d) items", len(res), max)
+			break Loop
 		}
 	}