WebSocket报错“Unexpected response code: 502 ”

Question

WebSocket connection to 'ws://foo.bar/socket.io/1/websocket/oBVUe9G9fBFksDrdt-ze' failed: Error during WebSocket handshake: Unexpected response code: 502
每次连接远程服务端都会在本地客户端报这个502Error，服务端也会报同样Error，但是又能连接上，就是说两端都能通讯，这是什么回事？