Replace service annotations when updating services.

In case the whole annotation changes (like the external DNS) we
don't want to keep the old one hanging around. Unline specs, we
don't expect anyone except the operator to change the annotations.

Use StrategicMergePatchType in order to replace the annotations
map completely.

pkg/cluster/resources.go

@@ -250,6 +250,20 @@ func (c *Cluster) updateService(role PostgresRole, newService *v1.Service) error
 	}
 	serviceName := util.NameFromMeta(c.Service[role].ObjectMeta)
 
+	if len(newService.ObjectMeta.Annotations) > 0 {
+
+		annotationsPatchData := metadataAnnotationsPatch(newService.ObjectMeta.Annotations)
+
+		_, err := c.KubeClient.Services(c.Service[role].Namespace).Patch(
+			c.Service[role].Name,
+			api.StrategicMergePatchType,
+			[]byte(annotationsPatchData), "")
+
+		if err != nil {
+			return fmt.Errorf("could not replace annotations for the service '%s': %v", serviceName, err)
+		}
+	}
+
 	patchData, err := specPatch(newService.Spec)
 	if err != nil {
 		return fmt.Errorf("could not form patch for the service '%s': %v", serviceName, err)
@@ -267,6 +281,7 @@ func (c *Cluster) updateService(role PostgresRole, newService *v1.Service) error
 	return nil
 }
 
+
 func (c *Cluster) deleteService(role PostgresRole) error {
 	c.logger.Debugf("Deleting service %s", role)
 	if c.Service[role] == nil {

pkg/cluster/util.go

@@ -63,6 +63,16 @@ func specPatch(spec interface{}) ([]byte, error) {
 	}{spec})
 }
 
+func metadataAnnotationsPatch(annotations map[string]string) (string) {
+	annotationsList := make([]string, 0, len(annotations))
+
+	for name, value := range(annotations) {
+		annotationsList = append(annotationsList, fmt.Sprintf(`"%s":"%s"`, name, value))
+	}
+	annotationsString := strings.Join(annotationsList, ",")
+	return fmt.Sprintf(`{"metadata":{"annotations": {"$patch":"replace", %s}}}`, annotationsString)
+}
+
 func (c *Cluster) logStatefulSetChanges(old, new *v1beta1.StatefulSet, isUpdate bool, reasons []string) {
 	if isUpdate {
 		c.logger.Infof("statefulset '%s' has been changed",