plugin/kubernetes: don't return when ServerVersion return an error (#4490)

When err=nil try to determine the version of the k8s cluster and disable
endpoint slices. Don't return from connecting to the cluster.

In the future we should just default to true, and delete all this code.
Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/kubernetes/kubernetes.go

@@ -252,15 +252,14 @@ func (k *Kubernetes) InitKubeCache(ctx context.Context) (err error) {
 	}
 	// Disable use of endpoint slices for k8s versions 1.18 and earlier. Endpoint slices were
 	// introduced in 1.17 but EndpointSliceMirroring was not added until 1.19.
-	sv, err := kubeClient.ServerVersion()
-	if err != nil {
-		return err
-	}
-	major, _ := strconv.Atoi(sv.Major)
-	minor, _ := strconv.Atoi(strings.TrimRight(sv.Minor, "+"))
-	if k.opts.useEndpointSlices && major <= 1 && minor <= 18 {
-		log.Info("watching Endpoints instead of EndpointSlices in k8s versions < 1.19")
-		k.opts.useEndpointSlices = false
+	// if err != nil, we continue with the above default which is to use endpoint slices.
+	if sv, err := kubeClient.ServerVersion(); err == nil {
+		major, _ := strconv.Atoi(sv.Major)
+		minor, _ := strconv.Atoi(strings.TrimRight(sv.Minor, "+"))
+		if k.opts.useEndpointSlices && major <= 1 && minor <= 18 {
+			log.Info("Watching Endpoints instead of EndpointSlices in k8s versions < 1.19")
+			k.opts.useEndpointSlices = false
+		}
 	}
 
 	k.APIConn = newdnsController(ctx, kubeClient, k.opts)