Cluster adapter

How it works

The Cluster adapter allows to use Socket.IO within a Node.js cluster.

Every packet that is sent to multiple clients (e.g. io.to("room1").emit() or socket.broadcast.emit()) is also sent to other workers via the IPC channel.

The source code of this adapter can be found here.

Installation

npm install @socket.io/cluster-adapter

Usage

With Node.js cluster

const cluster = require("cluster");
const http = require("http");
const { Server } = require("socket.io");
const numCPUs = require("os").cpus().length;
const { setupMaster, setupWorker } = require("@socket.io/sticky");
const { createAdapter, setupPrimary } = require("@socket.io/cluster-adapter");

if (cluster.isMaster) {
  console.log(`Master ${process.pid} is running`);

  const httpServer = http.createServer();

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

  // setup connections between the workers
  setupPrimary();

  // needed for packets containing buffers (you can ignore it if you only send plaintext objects)
  // Node.js < 16.0.0
  cluster.setupMaster({
    serialization: "advanced",
  });
  // Node.js > 16.0.0
  // cluster.setupPrimary({
  //   serialization: "advanced",
  // });

  httpServer.listen(3000);

  for (let i = 0; i < numCPUs; i++) {
    cluster.fork();
  }

  cluster.on("exit", (worker) => {
    console.log(`Worker ${worker.process.pid} died`);
    cluster.fork();
  });
} else {
  console.log(`Worker ${process.pid} started`);

  const httpServer = http.createServer();
  const io = new Server(httpServer);

  // use the cluster adapter
  io.adapter(createAdapter());

  // setup connection with the primary process
  setupWorker(io);

  io.on("connection", (socket) => {
    /* ... */
  });
}

With PM2

See the associated documentation.

With recluster

cluster.js

const cluster = require("cluster");
const http = require("http");
const { setupMaster } = require("@socket.io/sticky");
const { setupPrimary } = require("@socket.io/cluster-adapter");
const recluster = require("recluster");
const path = require("path");

const httpServer = http.createServer();

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

// setup connections between the workers
setupPrimary();

// needed for packets containing buffers (you can ignore it if you only send plaintext objects)
// Node.js < 16.0.0
cluster.setupMaster({
  serialization: "advanced",
});
// Node.js > 16.0.0
// cluster.setupPrimary({
//   serialization: "advanced",
// });

httpServer.listen(3000);

const balancer = recluster(path.join(__dirname, "worker.js"));

balancer.run();

worker.js

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

const httpServer = http.createServer();
const io = new Server(httpServer);

// use the cluster adapter
io.adapter(createAdapter());

// setup connection with the primary process
setupWorker(io);

io.on("connection", (socket) => {
  /* ... */
});

Options

Name	Description	Default value
requestsTimeout	the timeout for inter-server requests such as fetchSockets() or serverSideEmit() with ack	5000