nginx 代理 web socket 报错“WebSocket is already in CLOSING or CLOSED state.”

在生产环境中需要使用 nginx 代理 websocket ，按照正常配置之后发现浏览器一直提示 “WebSocket is already in CLOSING or CLOSED state.”

这是因为 nginx 在代理需要添加如下两个参数

           proxy_set_header Upgrade $http_upgrade;
           proxy_set_header Connection "upgrade";