on node, cluster, express and creating multiple connections

June 02, 2021, at 8:50 PM

I have a node.js server running with cluster,, express, and to create stickiness (We also use Redis for cross communication but I am not sure that is an issue). I have one client type (iOS React-Native) that uses polling, hence the need for sticky. The socket connection created from this client uses polling and is making multiple socket connections to the server. Here is an example from my logs (6680 and 6674 are PIDS from the workers)

 process: 6680, 2021-06-01T15:48:02.941Z, socketManager, io.sockets.on(connect), Will broadcast HELLO JfLCgyTZmvMcpMgzAAFZ
 process: 6674, 2021-06-01T15:48:05.127Z, socketManager, io.sockets.on(connect), Will broadcast HELLO MCAoSsuLNuiGe2o3AAED
process: 6680, 2021-06-01T15:48:06.989Z, socketManager, io.sockets.on(connect), Will broadcast HELLO LzxAW4_1Fhk3D4cdAAFa

It initially connects to the process on 6680 and then 6674 and then back to 6680. It was my understanding that "sticky" should have prevented this hopping around.

Here are some relevant bits from my server setup:

const express = require('express');
const app = express();
const cluster = require('cluster');
const { setupMaster, setupWorker } = require('');
if (cluster.isMaster) {
  console.log(`Master is started with process ID ${}`);
  const serverhttp =
    process.env.NODE_ENV === 'production'
      ? https.createServer(options, app)
      : http.Server(app);
  setupMaster(serverhttp, {
    loadBalancingMethod: 'least-connection', // either "random", "round-robin" or "least-connection"
 for (let i = 0; i < numCPUs; i++) {
  cluster.on('exit', (worker) => {
    console.log(`Worker died on process ID ${}`);
} else {
console.log(`Worker started at process ID ${}`);
  app.use(bodyParser.urlencoded({ extended: false }));
  const serverhttp =
    process.env.NODE_ENV === 'production'
      ? https.createServer(options, app)
      : http.Server(app);
/* app.use routes, cors, static routes; db connection initialization */
const io = socketManager(serverhttp, redisCache); // initialize socket
  serverhttp.listen(port, () => {
    console.log(`Starting server on ${port}`);
  serverhttp.keepAliveTimeout = 65 * 1000;
  serverhttp.headersTimeout = 66 * 1000;

socketManager here encapsulates the socket connection creation and all of the events tied to it. (redisCache is simply a user management cache.

The module simply exports the socket configuration code:

 module.exports = function (serverhttp, redisClient) {
  const config = {
    pingTimeout: 60000,
    pingInterval: 25000,
    transports: ['polling','websocket'], 
  const io = socketio.listen(serverhttp, config);
//Redis Adapter
      host: REDIS_HOST,
      port: REDIS_PORT,
//Support functions....

 io.sockets.on('connection', function (client) {
    logIt('io.sockets.on(connect)', `Will broadcast HELLO ${}`);
    io.emit('HELLO', `from io.emit -- ${}`);
    client.on(USER_CONNECTED, async (user) => {
      logIt('client.on(USER_CONNECTED)', ` ${} ${}`);
      user.socketId =;
      const redisContent= await redisClient.addRedisUser({
     io.emit(USER_CONNECTED, user); // broadcast to other clients
   //other events
return io; //End of module exports function

My configuration is not that different than code sample at multiple nodes. Except for two things:

  1. My master is NOT listening, but my workers are. (And this is a big difference, I will admit)
  2. My io.sockets.on (or io.on) are initiated before the setupWorker is called.

On 1 have tried shifting to listen only on the master but then I do not get the static routes and I get a web error (cannot GET / ). When I shift the app.use content to be configured with the master the page comes up but I never see the socket connections being made and the DB connection times out even though it is initialized. (The "Hello" log from above are never issued.) The one thing missing from the site example is express.

On 2, I am not sure why this would make a difference.

So, is there some way to shift my master/worker configuration around such that it is using the sticky functionality and uses express but can also get the worker instances to respond on a client connection?
Is my express/https server/socket io implementation misconfigured in some way? Is there a way to get express/https to listen at both the master and the worker level. It would seem to me that while I am connecting through the master it is not being passed to a worker.

Thanks -- Josef

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