plugin/kubernetes: Add support for topology-aware headless services via "az-pinned" subdomains (#8388)

plugin/kubernetes/object/endpoint.go

@@ -2,6 +2,8 @@ package object
 
 import (
 	"fmt"
+	"maps"
+	"strings"
 
 	discovery "k8s.io/api/discovery/v1"
 	meta "k8s.io/apimachinery/pkg/apis/meta/v1"
@@ -17,6 +19,12 @@ type Endpoints struct {
 	Index     string
 	IndexIP   []string
 	Subsets   []EndpointSubset
+	// Zones maps address IPs to their topology.kubernetes.io/zone,
+	// lowercased. Nil unless the kubernetes plugin's `zonal` option
+	// selected the zone-retaining transform, so default configurations
+	// carry one nil pointer per slice and their addresses stay exactly
+	// as slim as before.
+	Zones map[string]string
 
 	*Empty
 }
@@ -48,6 +56,18 @@ func EndpointsKey(name, namespace string) string { return name + "." + namespace
 
 // EndpointSliceToEndpoints converts a *discovery.EndpointSlice to a *Endpoints.
 func EndpointSliceToEndpoints(obj meta.Object) (meta.Object, error) {
+	return endpointSliceToEndpoints(obj, false /* withZones */)
+}
+
+// EndpointSliceToEndpointsWithZones is EndpointSliceToEndpoints, but also
+// retains each endpoint's topology zone. Used only when the kubernetes
+// plugin's zonal option is enabled, so the default configuration's cache
+// stays exactly as slim as before.
+func EndpointSliceToEndpointsWithZones(obj meta.Object) (meta.Object, error) {
+	return endpointSliceToEndpoints(obj, true /* withZones */)
+}
+
+func endpointSliceToEndpoints(obj meta.Object, withZones bool) (meta.Object, error) {
 	ends, ok := obj.(*discovery.EndpointSlice)
 	if !ok {
 		return nil, fmt.Errorf("unexpected object %v", obj)
@@ -92,6 +112,14 @@ func EndpointSliceToEndpoints(obj meta.Object) (meta.Object, error) {
 			if end.Hostname != nil {
 				ea.Hostname = *end.Hostname
 			}
+			if withZones && end.Zone != nil {
+				if e.Zones == nil {
+					e.Zones = make(map[string]string)
+				}
+				// Lowercased once here: qnames arrive case-folded, so
+				// lookups compare without folding per query.
+				e.Zones[a] = strings.ToLower(*end.Zone)
+			}
 			// ignore pod names that are too long to be a valid label
 			if end.TargetRef != nil && len(end.TargetRef.Name) < 64 {
 				ea.TargetRefName = end.TargetRef.Name
@@ -144,6 +172,9 @@ func (e *Endpoints) DeepCopyObject() runtime.Object {
 		Subsets:   make([]EndpointSubset, len(e.Subsets)),
 	}
 	copy(e1.IndexIP, e.IndexIP)
+	if e.Zones != nil {
+		e1.Zones = maps.Clone(e.Zones)
+	}
 
 	for i, eps := range e.Subsets {
 		sub := EndpointSubset{