An example multiprocessing (cluster) Node.js server application. #node.js #multiprocessing #express #cluster

cluster-server.js

var cluster = require('cluster'); 

var server = null;
var workers = null;
var info = null;

const TIMEOUT = 5;
const N = 2;

if (cluster.isMaster) {
  // Master process

  info = console.info.bind(undefined, '[master #' +  process.pid + ']')
  
  workers = new Array(N);
  info('Spawning ' + N + ' workers...')
  for (let i = 0; i < N; i++) {
    workers[i] = cluster.fork();
  }
  
  let numWorkers = N; 
  let shutdown = function ()
  {
    info('Shutting down workers...')
    for (let worker of workers) {
      // Send a message to workers so they can gracefully stop
      worker.send('shutdown');
      worker.on('exit', function () {
        if (--numWorkers == 0) {
          info('All workers have finished. Exiting')
          process.exit(0)
        }
      })
    }
  };

  process.on('SIGTERM', shutdown);
  process.on('SIGINT', shutdown);

} else {
  // Worker process 
  
  info = console.info.bind(undefined, '[worker #' + process.pid + ']')
  
  let app = require("./app") // an Express application
  server = app.listen(3001, function () {
    info('Started');
  });

  process.on('message', function (msg) {
    switch (msg) {
      case 'shutdown':
        info('Received shutdown request from master: Closing connections...')
        // Stop accepting connections, wait until existing connections close
        server.close(function () {
          info('Closed all connections.')
          process.exit(0);
        });
        setTimeout(function () {
          info('Forcefully shutting down (some connections maybe still alive)')
          process.exit(1);
        }, TIMEOUT *1e+3)
        break;
      default:
        break;
    }
  });
  
  // Ignore direct OS signals on workers; workers should only be
  // controlled by the master process.
  let ignore = function () {
    info('Ignoring direct signal to worker...')
  }
  process.on('SIGTERM', ignore);
  process.on('SIGINT', ignore);
}