endpoinslices must mirror services labels

Implement, in the endpoint slice controller, the same logic
used for labels in the legacy endpoints controller.

The labels in the endpoint and in the parent must be equivalent.
Headless services add the well-known IsHeadlessService label.
Slices must have two well known labels: LabelServiceName and
LabelManagedBy.

pkg/controller/endpointslice/utils.go

@@ -21,6 +21,7 @@ import (
 	"time"
 
 	corev1 "k8s.io/api/core/v1"
+	v1 "k8s.io/api/core/v1"
 	discovery "k8s.io/api/discovery/v1beta1"
 	apiequality "k8s.io/apimachinery/pkg/api/equality"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
@@ -30,6 +31,7 @@ import (
 	"k8s.io/klog/v2"
 	podutil "k8s.io/kubernetes/pkg/api/v1/pod"
 	api "k8s.io/kubernetes/pkg/apis/core"
+	helper "k8s.io/kubernetes/pkg/apis/core/v1/helper"
 	"k8s.io/kubernetes/pkg/apis/discovery/validation"
 	endpointutil "k8s.io/kubernetes/pkg/controller/util/endpoint"
 	utilnet "k8s.io/utils/net"
@@ -152,12 +154,9 @@ func endpointsEqualBeyondHash(ep1, ep2 *discovery.Endpoint) bool {
 func newEndpointSlice(service *corev1.Service, endpointMeta *endpointMeta) *discovery.EndpointSlice {
 	gvk := schema.GroupVersionKind{Version: "v1", Kind: "Service"}
 	ownerRef := metav1.NewControllerRef(service, gvk)
-	return &discovery.EndpointSlice{
+	epSlice := &discovery.EndpointSlice{
 		ObjectMeta: metav1.ObjectMeta{
-			Labels: map[string]string{
-				discovery.LabelServiceName: service.Name,
-				discovery.LabelManagedBy:   controllerName,
-			},
+			Labels:          map[string]string{},
 			GenerateName:    getEndpointSlicePrefix(service.Name),
 			OwnerReferences: []metav1.OwnerReference{*ownerRef},
 			Namespace:       service.Namespace,
@@ -166,6 +165,10 @@ func newEndpointSlice(service *corev1.Service, endpointMeta *endpointMeta) *disc
 		AddressType: endpointMeta.AddressType,
 		Endpoints:   []discovery.Endpoint{},
 	}
+	// add parent service labels
+	epSlice.Labels, _ = setEndpointSliceLabels(epSlice, service)
+
+	return epSlice
 }
 
 // getEndpointSlicePrefix returns a suitable prefix for an EndpointSlice name.
@@ -267,6 +270,62 @@ func serviceControllerKey(endpointSlice *discovery.EndpointSlice) (string, error
 	return fmt.Sprintf("%s/%s", endpointSlice.Namespace, serviceName), nil
 }
 
+// setEndpointSliceLabels returns a map with the new endpoint slices labels and true if there was an update.
+// Slices labels must be equivalent to the Service labels except for the reserved IsHeadlessService, LabelServiceName and LabelManagedBy labels
+// Changes to IsHeadlessService, LabelServiceName and LabelManagedBy labels on the Service do not result in updates to EndpointSlice labels.
+func setEndpointSliceLabels(epSlice *discovery.EndpointSlice, service *corev1.Service) (map[string]string, bool) {
+	updated := false
+	epLabels := make(map[string]string)
+	svcLabels := make(map[string]string)
+
+	// check if the endpoint slice and the service have the same labels
+	// clone current slice labels except the reserved labels
+	for key, value := range epSlice.Labels {
+		if IsReservedLabelKey(key) {
+			continue
+		}
+		// copy endpoint slice labels
+		epLabels[key] = value
+	}
+
+	for key, value := range service.Labels {
+		if IsReservedLabelKey(key) {
+			klog.Warningf("Service %s/%s using reserved endpoint slices label, skipping label %s: %s", service.Namespace, service.Name, key, value)
+			continue
+		}
+		// copy service labels
+		svcLabels[key] = value
+	}
+
+	// if the labels are not identical update the slice with the corresponding service labels
+	if !apiequality.Semantic.DeepEqual(epLabels, svcLabels) {
+		updated = true
+	}
+
+	// add or remove headless label depending on the service Type
+	if !helper.IsServiceIPSet(service) {
+		svcLabels[v1.IsHeadlessService] = ""
+	} else {
+		delete(svcLabels, v1.IsHeadlessService)
+	}
+
+	// override endpoint slices reserved labels
+	svcLabels[discovery.LabelServiceName] = service.Name
+	svcLabels[discovery.LabelManagedBy] = controllerName
+
+	return svcLabels, updated
+}
+
+// IsReservedLabelKey return true if the label is one of the reserved label for slices
+func IsReservedLabelKey(label string) bool {
+	if label == discovery.LabelServiceName ||
+		label == discovery.LabelManagedBy ||
+		label == v1.IsHeadlessService {
+		return true
+	}
+	return false
+}
+
 // endpointSliceEndpointLen helps sort endpoint slices by the number of
 // endpoints they contain.
 type endpointSliceEndpointLen []*discovery.EndpointSlice