upstream ws {
    server 1.1.1.1:8888;
}
server {
     server_name aa.ym;
     listen 80;
     location / {
         proxy_pass http://ws;
         proxy_read_timeout 300s;
         proxy_send_timeout 300s;
         
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
         
         proxy_http_version 1.1;
         proxy_set_header Upgrade $http_upgrade;
         proxy_set_header Connection $connection_upgrade;
     }
}

最重要的就是在反向代理的配置中增加了如下两行

proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection $connection_upgrade;

这里面的关键部分在于HTTP的请求中多了如下头部：

Upgrade: websocket
Connection: Upgrade

这两个字段表示请求服务器升级协议为WebSocket。服务器处理完请求后，响应如下报文：

// 状态码为101
HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: upgrade