code: func (s *Server) Start() {
  
  	http.HandleFunc("/", index)
  	http.Handle("/stats/app", &statsHandler{
  		stats:  s.Stats,
  		logger: s.Logger,
  	})
  	http.HandleFunc("/stats/runtime", stats_api.Handler)
  
  	port := DefaultPort
  	if p := os.Getenv(EnvPort); p != "" {
  		port = p
  	}
  
  	s.Logger.Printf("[INFO] Start server listening on :%s", port)
  	if err := http.ListenAndServe(":"+port, nil); err != nil {
  		s.Logger.Printf("[ERROR] Failed to start varz-server: %s", err)
  	}
  }
docs: // Start starts listening.