KEP 1645: add labels and annotations export

Signed-off-by: Arthur Outhenin-Chalandre <arthur@cri.epita.fr>

keps/sig-multicluster/1645-multi-cluster-services-api/README.md

@@ -107,6 +107,7 @@ tags, and then generate with `hack/update-toc.sh`.
     - [Service Port](#service-port)
     - [Headlessness](#headlessness)
     - [Session Affinity](#session-affinity)
+    - [Labels and Annotation](#labels-and-annotations)
   - [Test Plan](#test-plan)
   - [Graduation Criteria](#graduation-criteria)
     - [Alpha -> Beta Graduation](#alpha---beta-graduation)
@@ -119,6 +120,7 @@ tags, and then generate with `hack/update-toc.sh`.
   - [Export services via label selector](#export-services-via-label-selector)
   - [Export via annotation](#export-via-annotation)
   - [Other conflict resolution algorithms](#other-conflict-resolution-algorithms)
+  - [Exporting labels/annotations from the Service/ServiceExport objects](#exporting-labelsannotations-from-the-serviceserviceexport-objects)
 - [Infrastructure Needed](#infrastructure-needed)
 <!-- /toc -->
 
@@ -413,9 +415,19 @@ type ServiceExport struct {
         // +optional
         metav1.ObjectMeta `json:"metadata,omitempty"`
         // +optional
+        Spec ServiceExportSpec `json:"spec,omitempty"`
+        // +optional
         Status ServiceExportStatus `json:"status,omitempty"`
 }
 
+// ServiceExportSpec describes an exported service and extra exported information
+type ServiceExportSpec struct {
+        // +optional
+        ExportedLabels map[string]string `json:"exportedLabels"`
+        // +optional
+        ExportedAnnotations map[string]string `json:"exportedAnnotations"`
+}
+
 // ServiceExportStatus contains the current status of an export.
 type ServiceExportStatus struct {
         // +optional
@@ -497,9 +509,12 @@ single authority across all clusters. It is that authority’s responsibility to
 ensure that a name is shared by multiple services within the namespace if and
 only if they are instances of the same service.
 
-All information about the service, including ports, backends and topology, will
-continue to be stored in the `Service` objects, which are each name mapped to a
-`ServiceExport`.
+Most information about the service, including ports, backends, topology and
+session affinity, will continue to be stored in the `Service` objects, which
+are each name mapped to a `ServiceExport`. This does not apply for labels and
+annotations which are stored in `ServiceExport` directly in the spec in `exportedLabels`
+and `exportedAnnotations`. Implementations must not export the annotations or
+labels from the metadata of the `Service` or `ServiceExport` resources.
 
 Deleting a `ServiceExport` will stop exporting the name-mapped `Service`.
 
@@ -1013,6 +1028,12 @@ Session affinity affects a service as a whole for a given consumer. The derived
 service's session affinity will be decided according to the conflict resolution
 policy.
 
+#### Labels and annotations
+
+Labels and Services affects a service as a whole for a given consumer. The derived
+service's labels and annotations will be decided according to the conflict resolution
+if the maps are not identical.
+
 ### Test Plan
 
 E2E tests can use [kind](https://kind.sigs.k8s.io/) to create multiple clusters
@@ -1229,7 +1250,7 @@ retain the flexibility of selectors.
 
 ### Export via annotation
 
-`ServiceExport` as described has no spec and seems like it could just be
+`ServiceExport` as described has almost no spec and seems like it could just be
 replaced with an annotation, e.g. `multicluster.kubernetes.io/export`. When a
 service is found with the annotation, it would be considered marked for export
 to the clusterset. The controller would then create `EndpointSlices` and an
@@ -1258,6 +1279,19 @@ more confusing for users. Having just one simple deciding factor based on
 ServiceExport oldness makes resolving conflicts straightforward, and this
 alternative conflict resolution algorithm could hinder this ease of use.
 
+### Exporting labels/annotations from the Service/ServiceExport objects
+
+`Service` and `ServiceExport` have labels and annotations which could be used during
+export and propagated to the `ServiceImport`. In that case as both `Service` and
+`ServiceExport` have those fields in the metadata object it becomes less clear what
+labels and annotations exported. For instance, should an implementation merge the
+labels/annotations from both objects? Should it favor one? Should it takes only
+from the `Service` object?
+
+We also favored dedicated fields on the `ServiceExport` resource to give more
+flexibility as it will allow to export labels and annotations fully decorrelated
+from the `Service` and `ServiceExport` metadata.
+
 ## Infrastructure Needed
 <!--
 Use this section if you need things from the project/SIG.  Examples include a