plugin/kubernetes: support pods with multiple IPs (#8635)

The Pod object stored only the primary pod IP (status.podIP), causing
PodIndex lookups to fail for IPv6 clients in dual-stack clusters. This
prevented the metadata plugin from populating client-pod-name and
client-namespace.

Replace the PodIP string field with a PodIPs []string slice populated
from status.podIPs, and update podIPIndexFunc to index all IPs.

Signed-off-by: Christian Norbert Menges <christian.norbert.menges@sap.com>

plugin/kubernetes/object/pod.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"fmt"
 	"maps"
+	"slices"
 
 	api "k8s.io/api/core/v1"
 	meta "k8s.io/apimachinery/pkg/apis/meta/v1"
@@ -14,7 +15,7 @@ import (
 type Pod struct {
 	// Don't add new fields to this struct without talking to the CoreDNS maintainers.
 	Version   string
-	PodIP     string
+	PodIPs    []string
 	Name      string
 	Namespace string
 	Labels    map[string]string
@@ -30,9 +31,13 @@ func ToPod(obj meta.Object) (meta.Object, error) {
 	if !ok {
 		return nil, fmt.Errorf("unexpected object %v", obj)
 	}
+	podIPs := make([]string, len(apiPod.Status.PodIPs))
+	for i, pip := range apiPod.Status.PodIPs {
+		podIPs[i] = pip.IP
+	}
 	pod := &Pod{
 		Version:   apiPod.GetResourceVersion(),
-		PodIP:     apiPod.Status.PodIP,
+		PodIPs:    podIPs,
 		Namespace: apiPod.GetNamespace(),
 		Name:      apiPod.GetName(),
 		Labels:    apiPod.GetLabels(),
@@ -55,7 +60,7 @@ var _ runtime.Object = &Pod{}
 func (p *Pod) DeepCopyObject() runtime.Object {
 	p1 := &Pod{
 		Version:   p.Version,
-		PodIP:     p.PodIP,
+		PodIPs:    slices.Clone(p.PodIPs),
 		Namespace: p.Namespace,
 		Name:      p.Name,
 		// maps.Clone returns nil for a nil map, so an unlabelled pod stays unlabelled.