Merge pull request #46522 from MrHohn/fix-proxy-healthz

Automatic merge from submit-queue (batch tested with PRs 46252, 45524, 46236, 46277, 46522)

Add /healthz back to kube-proxy metrics server

Fixes #46447.

/healthz is removed from kube-proxy metrics server by #44968 and that breaks our upgrade test, which run 1.6 tests on 1.7 cluster. It seems harmless to continue holding /healthz on metrics server as well, so that we won't break other potential users.

/assign @bowei 
cc @dchen1107 

**Release note**:

```release-note
NONE
```

cmd/kube-proxy/app/BUILD

@@ -53,6 +53,7 @@ go_library(
         "//vendor/k8s.io/apimachinery/pkg/util/net:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/util/runtime:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/util/wait:go_default_library",
+        "//vendor/k8s.io/apiserver/pkg/server/healthz:go_default_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",

cmd/kube-proxy/app/server.go

@@ -38,6 +38,7 @@ import (
 	utilnet "k8s.io/apimachinery/pkg/util/net"
 	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
 	"k8s.io/apimachinery/pkg/util/wait"
+	"k8s.io/apiserver/pkg/server/healthz"
 	utilfeature "k8s.io/apiserver/pkg/util/feature"
 	clientgoclientset "k8s.io/client-go/kubernetes"
 	v1core "k8s.io/client-go/kubernetes/typed/core/v1"
@@ -630,6 +631,7 @@ func (s *ProxyServer) Run() error {
 	// Start up a metrics server if requested
 	if len(s.MetricsBindAddress) > 0 {
 		mux := http.NewServeMux()
+		healthz.InstallHandler(mux)
 		mux.HandleFunc("/proxyMode", func(w http.ResponseWriter, r *http.Request) {
 			fmt.Fprintf(w, "%s", s.ProxyMode)
 		})