为 Socket.io 配置 Nginx - 502 错误网关

Question

我正在尝试将 Node + Express + Socket.io 组成的应用程序配置为我的服务器上的生产环境，但几个小时后我仍然遇到相同的错误。

索引.js：

var express = require('express');
var app = express();
var server = require('http').createServer(app);


var io = require('socket.io')(server);
server.listen(3000);

索引.twig

    <script src="/node_modules/jquery/dist/jquery.js"></script>
    <script src="/socket.io/socket.io.js"></script>
    <script>  
        const socket = io();
...

配置 Nginx

server {
        listen 80;
        server_name sub.domain.com;
    location / {
        proxy_pass http://127.0.0.1:3000/;
    }
    location /socket.io/ {
         proxy_set_header Upgrade $http_upgrade;
         proxy_set_header Connection "upgrade";
         proxy_http_version 1.1;
         proxy_set_header Host $host;
         proxy_pass http://127.0.0.1:3000/socket.io/; 
    }

}

错误 502 我明白了：

socket.io/socket.io.js net::ERR_ABORTED 502 (Bad Gateway)