fix metrics for placeholder slice

There is always a placeholder slice.

The ServicePortCache logic was considering always one endpointSlice
per Endpoint, but if there are multiple empty Endpoints, we just
use one placeholder slice, not multiple placeholder slices.

pkg/controller/endpointslice/metrics/cache.go

@@ -91,6 +91,10 @@ func (spc *ServicePortCache) totals(maxEndpointsPerSlice int) (int, int, int) {
 		actualSlices += eInfo.Slices
 		desiredSlices += numDesiredSlices(eInfo.Endpoints, maxEndpointsPerSlice)
 	}
+	// there is always a placeholder slice
+	if desiredSlices == 0 {
+		desiredSlices = 1
+	}
 	return actualSlices, desiredSlices, endpoints
 }
 
@@ -148,6 +152,9 @@ func (c *Cache) updateMetrics() {
 // numDesiredSlices calculates the number of EndpointSlices that would exist
 // with ideal endpoint distribution.
 func numDesiredSlices(numEndpoints, maxEndpointsPerSlice int) int {
+	if numEndpoints == 0 {
+		return 0
+	}
 	if numEndpoints <= maxEndpointsPerSlice {
 		return 1
 	}

pkg/controller/endpointslice/metrics/cache_test.go

@@ -60,6 +60,23 @@ func TestNumEndpointsAndSlices(t *testing.T) {
 	expectNumEndpointsAndSlices(t, c, 4, 4, 160)
 }
 
+func TestPlaceHolderSlice(t *testing.T) {
+	c := NewCache(int32(100))
+
+	p80 := int32(80)
+	p443 := int32(443)
+
+	pmKey80443 := endpointutil.NewPortMapKey([]discovery.EndpointPort{{Port: &p80}, {Port: &p443}})
+	pmKey80 := endpointutil.NewPortMapKey([]discovery.EndpointPort{{Port: &p80}})
+
+	sp := NewServicePortCache()
+	sp.Set(pmKey80, EfficiencyInfo{Endpoints: 0, Slices: 1})
+	sp.Set(pmKey80443, EfficiencyInfo{Endpoints: 0, Slices: 1})
+
+	c.UpdateServicePortCache(types.NamespacedName{Namespace: "ns1", Name: "svc1"}, sp)
+	expectNumEndpointsAndSlices(t, c, 1, 2, 0)
+}
+
 func expectNumEndpointsAndSlices(t *testing.T, c *Cache, desired int, actual int, numEndpoints int) {
 	t.Helper()
 	if c.numSlicesDesired != desired {

pkg/controller/endpointslice/reconciler.go

@@ -223,11 +223,11 @@ func (r *reconciler) reconcileByAddressType(service *corev1.Service, pods []*cor
 			slicesToDelete = slicesToDelete[:0]
 		} else {
 			slicesToCreate = append(slicesToCreate, placeholderSlice)
-			spMetrics.Set(endpointutil.NewPortMapKey(placeholderSlice.Ports), metrics.EfficiencyInfo{
-				Endpoints: 0,
-				Slices:    1,
-			})
 		}
+		spMetrics.Set(endpointutil.NewPortMapKey(placeholderSlice.Ports), metrics.EfficiencyInfo{
+			Endpoints: 0,
+			Slices:    1,
+		})
 	}
 
 	metrics.EndpointsAddedPerSync.WithLabelValues().Observe(float64(totalAdded))

pkg/controller/endpointslice/reconciler_test.go

@@ -481,7 +481,7 @@ func TestReconcile1EndpointSlice(t *testing.T) {
 		{
 			desc:        "Existing placeholder that's the same",
 			existing:    newEndpointSlice(&svc, &endpointMeta{Ports: []discovery.EndpointPort{}, AddressType: discovery.AddressTypeIPv4}),
-			wantMetrics: expectedMetrics{desiredSlices: 0, actualSlices: 0, desiredEndpoints: 0, addedPerSync: 0, removedPerSync: 0, numCreated: 0, numUpdated: 0, numDeleted: 0, slicesChangedPerSync: 0},
+			wantMetrics: expectedMetrics{desiredSlices: 1, actualSlices: 1, desiredEndpoints: 0, addedPerSync: 0, removedPerSync: 0, numCreated: 0, numUpdated: 0, numDeleted: 0, slicesChangedPerSync: 0},
 		},
 		{
 			desc:        "Existing placeholder that's different",