Adding new label to indicate what is managing an EndpointSlice

This adds a new Label to EndpointSlices that will ensure that multiple
controllers or entities can manage subsets of EndpointSlices. This
label provides a way to indicate the controller or entity responsible
for managing an EndpointSlice.

To provide a seamless upgrade from the alpha release of EndpointSlices
that did not support this label, a temporary annotation has been added
on Services to indicate that this label has been initially set on
EndpointSlices. That annotation will be set automatically by the
EndpointSlice controller with this commit once appropriate Labels have
been added on the corresponding EndpointSlices.

pkg/controller/endpointslice/endpointslice_controller.go

@@ -54,6 +54,20 @@ const (
 	// 5ms, 10ms, 20ms, 40ms, 80ms, 160ms, 320ms, 640ms, 1.3s, 2.6s, 5.1s,
 	// 10.2s, 20.4s, 41s, 82s
 	maxRetries = 15
+	// controllerName is a unique value used with LabelManagedBy to indicated
+	// the component managing an EndpointSlice.
+	controllerName = "endpointslice-controller.k8s.io"
+	// managedBySetupAnnotation is set on a Service to indicate that
+	// EndpointSlices for the Service have already been configured with
+	// LabelManagedBy. If this annotation is not set, all related EndpointSlices
+	// will have LabelManagedBy set to reference this controller if the label
+	// is not already set. Once all EndpointSlices are labeled, the Controller
+	// will set this annotation on the Service.
+	managedBySetupAnnotation = "endpointslice.kubernetes.io/managed-by-setup"
+	// managedBySetupCompleteValue represents the value of the
+	// managedBySetupAnnotation that indicates that the setup process has been
+	// completed for a Service.
+	managedBySetupCompleteValue = "true"
 )
 
 // NewController creates and initializes a new Controller
@@ -286,7 +300,28 @@ func (c *Controller) syncService(key string) error {
 		return err
 	}
 
-	esLabelSelector := labels.Set(map[string]string{discovery.LabelServiceName: service.Name}).AsSelectorPreValidated()
+	// With the goal of different controllers being able to manage different
+	// subsets of EndpointSlices, LabelManagedBy has been added to indicate
+	// which controller or entity manages an EndpointSlice. As part of this
+	// v1.16->v1.17 change, EndpointSlices will initially be assumed to be
+	// managed by this controller unless a label is set to indicate otherwise.
+	// To ensure a seamless upgrade process, the managedBySetupAnnotation is
+	// used to indicate that LabelManagedBy has been set initially for related
+	// EndpointSlices. If it hasn't been set to the expected value here, we call
+	// ensureSetupManagedByAnnotation() to set up LabelManagedBy on each
+	// EndpointSlice.
+	// TODO(robscott): Remove this before v1.18.
+	err = c.ensureSetupManagedByAnnotation(service)
+	if err != nil {
+		c.eventRecorder.Eventf(service, v1.EventTypeWarning, "FailedToSetEndpointSliceManagedByLabel",
+			"Error adding managed-by Label to Endpoint Slices for Service %s/%s: %v", service.Namespace, service.Name, err)
+		return err
+	}
+
+	esLabelSelector := labels.Set(map[string]string{
+		discovery.LabelServiceName: service.Name,
+		discovery.LabelManagedBy:   controllerName,
+	}).AsSelectorPreValidated()
 	endpointSlices, err := c.endpointSliceLister.EndpointSlices(service.Namespace).List(esLabelSelector)
 
 	if err != nil {
@@ -337,6 +372,49 @@ func (c *Controller) onServiceDelete(obj interface{}) {
 	c.queue.Add(key)
 }
 
+// ensureSetupManagedByAnnotation selects all EndpointSlices for a Service and
+// ensures they have LabelManagedBy set appropriately. This ensures that only
+// one controller or entity is trying to manage a given EndpointSlice. This
+// function provides backwards compatibility with the initial alpha release of
+// EndpointSlices that did not include these labels.
+// TODO(robscott): Remove this in time for v1.18.
+func (c *Controller) ensureSetupManagedByAnnotation(service *v1.Service) error {
+	if managedBySetup, ok := service.Annotations[managedBySetupAnnotation]; ok && managedBySetup == managedBySetupCompleteValue {
+		return nil
+	}
+
+	esLabelSelector := labels.Set(map[string]string{discovery.LabelServiceName: service.Name}).AsSelectorPreValidated()
+	endpointSlices, err := c.endpointSliceLister.EndpointSlices(service.Namespace).List(esLabelSelector)
+
+	if err != nil {
+		c.eventRecorder.Eventf(service, v1.EventTypeWarning, "FailedToListEndpointSlices",
+			"Error listing Endpoint Slices for Service %s/%s: %v", service.Namespace, service.Name, err)
+		return err
+	}
+
+	for _, endpointSlice := range endpointSlices {
+		if _, ok := endpointSlice.Labels[discovery.LabelManagedBy]; !ok {
+			if endpointSlice.Labels == nil {
+				endpointSlice.Labels = make(map[string]string)
+			}
+
+			endpointSlice.Labels[discovery.LabelManagedBy] = controllerName
+			_, err = c.client.DiscoveryV1alpha1().EndpointSlices(endpointSlice.Namespace).Update(endpointSlice)
+			if err != nil {
+				return err
+			}
+		}
+	}
+
+	if service.Annotations == nil {
+		service.Annotations = make(map[string]string)
+	}
+
+	service.Annotations[managedBySetupAnnotation] = managedBySetupCompleteValue
+	_, err = c.client.CoreV1().Services(service.Namespace).Update(service)
+	return err
+}
+
 func (c *Controller) addPod(obj interface{}) {
 	pod := obj.(*v1.Pod)
 	services, err := c.serviceSelectorCache.GetPodServiceMemberships(c.serviceLister, pod)