Fix 'kubectl proxy' to allow the /metrics page to be proxied, without breaking the previous proxy behavior

pkg/kubectl/proxy_server.go

@@ -28,17 +28,18 @@ import (
 
 // ProxyServer is a http.Handler which proxies Kubernetes APIs to remote API server.
 type ProxyServer struct {
+	mux *http.ServeMux
 	httputil.ReverseProxy
 }
 
 // NewProxyServer creates and installs a new ProxyServer.
 // It automatically registers the created ProxyServer to http.DefaultServeMux.
 func NewProxyServer(filebase string, apiProxyPrefix string, staticPrefix string, cfg *client.Config) (*ProxyServer, error) {
-	prefix := cfg.Prefix
-	if prefix == "" {
-		prefix = "/api"
+	host := cfg.Host
+	if !strings.HasSuffix(host, "/") {
+		host = host + "/"
 	}
-	target, err := url.Parse(singleJoiningSlash(cfg.Host, prefix))
+	target, err := url.Parse(host)
 	if err != nil {
 		return nil, err
 	}
@@ -46,15 +47,22 @@ func NewProxyServer(filebase string, apiProxyPrefix string, staticPrefix string,
 	if proxy.Transport, err = client.TransportFor(cfg); err != nil {
 		return nil, err
 	}
-	http.Handle(apiProxyPrefix, http.StripPrefix(apiProxyPrefix, proxy))
-	http.Handle(staticPrefix, newFileHandler(staticPrefix, filebase))
+	if strings.HasPrefix(apiProxyPrefix, "/api") {
+		proxy.mux.Handle(apiProxyPrefix, proxy)
+	} else {
+		proxy.mux.Handle(apiProxyPrefix, http.StripPrefix(apiProxyPrefix, proxy))
+	}
+	proxy.mux.Handle(staticPrefix, newFileHandler(staticPrefix, filebase))
 	return proxy, nil
 }
 
 // Serve starts the server (http.DefaultServeMux) on given port, loops forever.
 func (s *ProxyServer) Serve(port int) error {
-	addr := fmt.Sprintf(":%d", port)
-	return http.ListenAndServe(addr, nil)
+	server := http.Server{
+		Addr:    fmt.Sprintf(":%d", port),
+		Handler: s.mux,
+	}
+	return server.ListenAndServe()
 }
 
 func newProxyServer(target *url.URL) *ProxyServer {
@@ -63,7 +71,10 @@ func newProxyServer(target *url.URL) *ProxyServer {
 		req.URL.Host = target.Host
 		req.URL.Path = singleJoiningSlash(target.Path, req.URL.Path)
 	}
-	return &ProxyServer{ReverseProxy: httputil.ReverseProxy{Director: director}}
+	return &ProxyServer{
+		ReverseProxy: httputil.ReverseProxy{Director: director},
+		mux:          http.NewServeMux(),
+	}
 }
 
 func newFileHandler(prefix, base string) http.Handler {