Socketio usage with PM2 cluster mode

[sridhard]

Describe the bug
I am using socketio with PM2 and cluster mode.
I am using @socket.io/pm2. Also used socket.io/cluster-adapter and socket.io/sticky s per the docs.

In client side I changed transport to polling (Removed websocket).
With websocket in client side everything is working properly.
When using polling, client connects with server and disconnects.

To Reproduce

Please fill the following code example:

Versions:
"@socket.io/cluster-adapter": "^0.2.2",
"@socket.io/sticky": "^1.0.4",
"socket.io": "^4.7.5",

Server

const fp = require('fastify-plugin')
const { Server } = require("socket.io");
const { createAdapter } = require("@socket.io/cluster-adapter");
const { setupWorker } = require("@socket.io/sticky");

async function socketio(fastify, opts = {}) {
  console.log("Creating sockio");

  const io = new Server(fastify.server, opts);
  io.adapter(createAdapter());
  setupWorker(io);

  fastify.decorate("io", io);
  fastify.addHook("onClose", (fastify, done) => {
    fastify.io.close();
    done();
  });  
}

module.exports = fp(socketio);

module.exports = (fastify) => {
  fastify.ready().then(() => {
    fastify.io.on("connection", (socket) => {

      console.log(`New client connected via: ${socket.conn.transport.name}`);

      socket.conn.on("upgrade", () => {
        console.log(`Transport changed to ${socket.conn.transport.name}`);
      });

      socket.on("message", (msg) => {
        console.log("Message received over connection type : ", socket.conn.transport.name);
        socket.emit("reply", "Message received loud and clear!");
      });

      socket.on("disconnect", () => {
        console.log("Connection disconnected");
      });
    });
  });
};

Client

https://cdn.jsdelivr.net/npm/socket.io-client/dist/socket.io.js

    // Connect to the Socket.IO server
    const socket = io('https://chat.xyz.com', {
      transports:[ 'polling']
    }); // Connect to the local server

    // Function to append messages to the message div
    function appendMessage(message) {
      const messageDiv = document.getElementById('messages');
      const newMessage = document.createElement('div');
      newMessage.textContent = message;
      messageDiv.appendChild(newMessage);
    }

    // Listen for connection event
    socket.on('connect', () => {
      console.log('Connected to server');
      appendMessage('Connected to server');
    });

    socket.on('disconnect', () => {
      console.log('Disconnected from server');
      appendMessage('Disconnected from server');
    });

    // Listen for reply event
    socket.on('reply', (msg) => {
      console.log('Received reply:', msg);
      appendMessage(`Reply: ${msg}`);
    });

    // Listen for error event
    socket.on('error', (error) => {
      console.error('Error received from server:', error);
      appendMessage(`Error: ${error}`);
    });

    // Handle the send message button click
    document.getElementById('sendMessageButton').addEventListener('click', () => {
      const message = 'Hello from client';
      console.log('Sending message:', message);
      appendMessage(`Sent: ${message}`);
      socket.emit('message', message);
    });

Expected behavior
In polling mode pm2 sticky session should work and client should not get disconnect.

Platform:

• Device: mac chrome browser
• OS: Mac sonoma

Additional context
With websockets it is working. I am testing with polling for fallback support