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Forked from jdxcode/boot.js
Created Nov 9, 2015
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zero-downtime node.js app runner
// This script will boot app.js with the number of workers
// specified in WORKER_COUNT.
// The master will respond to SIGHUP, which will trigger
// restarting all the workers and reloading the app.
var cluster = require('cluster');
var workerCount = process.env.WORKER_COUNT || 2;
// Defines what each worker needs to run
// In this case, it's app.js a simple node http app
cluster.setupMaster({ exec: 'app.js' });
// Gets the count of active workers
function numWorkers() { return Object.keys(cluster.workers).length; }
var stopping = false;
// Forks off the workers unless the server is stopping
function forkNewWorkers() {
if (!stopping) {
for (var i = numWorkers(); i < workerCount; i++) { cluster.fork(); }
// A list of workers queued for a restart
var workersToStop = [];
// Stops a single worker
// Gives 60 seconds after disconnect before SIGTERM
function stopWorker(worker) {
var killTimer = setTimeout(function() {
}, 60000);
// Ensure we don't stay up just for this setTimeout
// Tell the next worker queued to restart to disconnect
// This will allow the process to finish it's work
// for 60 seconds before sending SIGTERM
function stopNextWorker() {
var i = workersToStop.pop();
var worker = cluster.workers[i];
if (worker) stopWorker(worker);
// Stops all the works at once
function stopAllWorkers() {
stopping = true;
console.log('stopping all workers');
for (var id in cluster.workers) {
// Worker is now listening on a port
// Once it is ready, we can signal the next worker to restart
cluster.on('listening', stopNextWorker);
// A worker has disconnected either because the process was killed
// or we are processing the workersToStop array restarting each process
// In either case, we will fork any workers needed
cluster.on('disconnect', forkNewWorkers);
// HUP signal sent to the master process to start restarting all the workers sequentially
process.on('SIGHUP', function() {
console.log('restarting all workers');
workersToStop = Object.keys(cluster.workers);
// Kill all the workers at once
process.on('SIGTERM', stopAllWorkers);
// Fork off the initial workers
console.log('app master',, 'booted');
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