How to set up Socket.IO using App Platform?

Hello everybody, I hope you are having a great day.


I have been trying to establish a websocket connection with my App Platform’s server component for a while and still no success. Surprisingly for me everything is working fine on my local machine.

Trouble description

After emitting a Socket.IO event from the Client I get only the following inside the networks’s request Preview (I don’t know how to attach the pictures in here) (DevTools screen,

You need to enable JavaScript to run this app.


I am using the node:cluster for my server. This code was doublechecked using the official Socket.IO docs for node:cluster.

if (cluster.isPrimary) {
  console.log("Primary cluster is running...");

  const httpServer = http.createServer(app);

  // setup sticky sessions
  setupMaster(httpServer, {
    loadBalancingMethod: "least-connection",

  // setup connections between the workers

  const primaryClusterPort = 3265;
  httpServer.listen(primaryClusterPort, () => {
    // Listen on the HTTP server in the worker process
    console.log(`Primary cluster running on port ${primaryClusterPort}...`);

  const workerCount = 2;
  for (let i = 0; i < workerCount; i++) {

  cluster.on("online", function (worker) {
    console.log("Worker " + + " is online");

  cluster.on("exit", function (worker, code, signal) {
      "Worker " + +
        " died with code: " +
        code +
        ", and signal: " +
    console.log("Starting a new worker");
} else {
  const httpServer = http.createServer(app); // Create the HTTP server in the worker process

  const io = new Server(httpServer, {
    cors: {
      origin: "*", // Allow all origins
      methods: ["GET", "POST"], // Allow GET and POST methods
      credentials: true, // Allow credentials


  // setup connection with the primary process

  io.on("connection", (socket) => {
    socket.on("exportExcel", (data) => {
      console.log("Socket on `exportExcel`: ", data);

      // for test
      socket.emit("exportExcel", { path: "export905.xlsx" });

  httpServer.listen(PORT, () => {
    // Listen on the HTTP server in the worker process
    console.log(`App listening on port ${PORT}...`);

I am using Node v18.12.1, Socket.IO v4.1.3 on the server, Socket.IO v4.6.1 on the client.

I hope anybody can help me and I am ready to provide any additional information if needed. Thank you in advance.

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