Allow kube-proxy using InClusterConfig()

cmd/kube-proxy/app/BUILD

@@ -66,6 +66,7 @@ go_library(
         "//vendor/k8s.io/apiserver/pkg/util/feature:go_default_library",
         "//vendor/k8s.io/client-go/kubernetes:go_default_library",
         "//vendor/k8s.io/client-go/kubernetes/typed/core/v1:go_default_library",
+        "//vendor/k8s.io/client-go/rest:go_default_library",
         "//vendor/k8s.io/client-go/tools/clientcmd:go_default_library",
         "//vendor/k8s.io/client-go/tools/clientcmd/api:go_default_library",
         "//vendor/k8s.io/client-go/tools/record:go_default_library",

cmd/kube-proxy/app/server.go

@@ -41,6 +41,7 @@ import (
 	utilfeature "k8s.io/apiserver/pkg/util/feature"
 	clientgoclientset "k8s.io/client-go/kubernetes"
 	v1core "k8s.io/client-go/kubernetes/typed/core/v1"
+	"k8s.io/client-go/rest"
 	"k8s.io/client-go/tools/clientcmd"
 	clientcmdapi "k8s.io/client-go/tools/clientcmd/api"
 	"k8s.io/client-go/tools/record"
@@ -393,15 +394,19 @@ type ProxyServer struct {
 // createClients creates a kube client and an event client from the given config and masterOverride.
 // TODO remove masterOverride when CLI flags are removed.
 func createClients(config componentconfig.ClientConnectionConfiguration, masterOverride string) (clientset.Interface, v1core.EventsGetter, error) {
-	if len(config.KubeConfigFile) == 0 && len(masterOverride) == 0 {
-		glog.Warningf("Neither --kubeconfig nor --master was specified. Using default API client. This might not work.")
-	}
+	var kubeConfig *rest.Config
+	var err error
 
+	if len(config.KubeConfigFile) == 0 && len(masterOverride) == 0 {
+		glog.Info("Neither kubeconfig file nor master URL was specified. Falling back to in-cluster config.")
+		kubeConfig, err = rest.InClusterConfig()
+	} else {
 		// This creates a client, first loading any specified kubeconfig
 		// file, and then overriding the Master flag, if non-empty.
-	kubeConfig, err := clientcmd.NewNonInteractiveDeferredLoadingClientConfig(
+		kubeConfig, err = clientcmd.NewNonInteractiveDeferredLoadingClientConfig(
 			&clientcmd.ClientConfigLoadingRules{ExplicitPath: config.KubeConfigFile},
 			&clientcmd.ConfigOverrides{ClusterInfo: clientcmdapi.Cluster{Server: masterOverride}}).ClientConfig()
+	}
 	if err != nil {
 		return nil, nil, err
 	}