Socket.IO not working on AWS with NGINX, Node.js, and HTTPS (400 Bad Request on WebSocket)

Question

I'm running a Node.js application with HTTPS and Socket.IO on an AWS EC2 instance, behind NGINX. The REST APIs work fine, but the WebSocket connection to Socket.IO fails with a 400 Bad Request.

const app = express();
const { createServer } = require("http");  // Use HTTP not HTTPS
const { Server } = require("socket.io");

const httpServer = createServer(app);
const io = new Server(httpServer, {
  cors: {
    origin: ['https://abcdDomain.com', 'http://localhost:3000'],
    methods: ["GET", "POST"],
    credentials: true
  }
});

io.on("connection", (socket) => {
  console.log("Socket connected:", socket.id);
});

httpServer.listen(3001, () => {
  console.log("HTTP server running on port 3001");
});

JoaoFCarvalho · Accepted Answer · 2025-06-20 17:32:26Z

1

According to documentation, when you get a 400 error when trying to connect, it usually means that

Usually, this means that a proxy in front of your server is not properly forwarding the WebSocket headers

Documentation also gives an example of the configuration you need to connect: Content of /etc/nginx/nginx.conf:

http {
  server {
    listen 80;

    location / {
      proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
      proxy_set_header Host $host;

      proxy_pass http://localhost:3000;

      proxy_http_version 1.1;
      proxy_set_header Upgrade $http_upgrade;
      proxy_set_header Connection "upgrade";
    }
  }
}

answered Jun 20 at 17:32

JoaoFCarvalho

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