Graceful cluster

Install:

npm install graceful-cluster

How to use

1. Enable graceful server shutdown

This patch will prevent active connections reset when server receives SIGKILL or SIGTERM. Idle (keep-alive) inbound connections without active requests will be destroyed.

Example 'server.js':

// Example server with 'express'.
var express = require('express');
var app = express();
var listener = app.listen(8000);
 
var GracefulServer = require('graceful-cluster').GracefulServer;
var gracefulServer = new GracefulServer({
    server: listener,
    shutdownTimeout: 10 * 1000,             // 10 sec.
});

GracefulServer options description:

option	info
log	function, custom log function, console.log used by default.
server	required, http server instance.
shutdownTimeout	ms, force worker shutdown on SIGTERM timeout. Defaults to 5000ms.

Also you can initiate graceful shutdown when needed:

gracefulServer.shutdown();

2. Use simplified cluster initialization

This cluster wrapper will send SIGTERM signal to workers and wait till they finished all requests.

Also it can gracefully restart all workers one by one with zero cluster downtime on some conditions:

1. Worker memory used.
2. Worker time online.
3. Your custom condition: just call GracefulCluster.gracefullyRestartCurrentWorker() to restart current worker in serverFunction.
4. On SIGUSR2 signal to cluster process.

Example 'cluster.js':

var GracefulCluster = require('graceful-cluster').GracefulCluster;
 
process.title = '<your-cluster-title>';     // Note, process title must be near filename (cluster.js) length, longer title truncated.
 
GracefulCluster.start({
    shutdownTimeout: 10 * 1000,             // 10 sec.
    restartOnTimeout: 5 * 3600 * 1000,      // 5 hours.
    restartOnMemory: 150 * 1024 * 1024,     // 150 MB.
    serverFunction: function() {
        require('./server');                // Your 'server.js' code module with server logic.
    }
});

GracefulCluster options description:

option	info
disableGraceful	disable graceful shutdown for faster debug.
exitFunction	optional, function that is called when the master needs to exit. The default function exits with exit code 0.
log	function, custom log function, console.log used by default.
restartOnMemory	bytes, optional. restart worker on memory usage.
restartOnTimeout	ms, optional. restart worker by timer.
serverFunction	required, function with worker logic.
shutdownTimeout	ms, optional. force worker shutdown on SIGTERM timeout. Defaults to 5000ms.
workersCount	workers count, if not specified os.cpus().length will be used.

Gracefully restart cluster

Graceful restart performed by USR2 signal:

pkill -USR2 <your-cluster-title>

or

kill -s SIGUSR2 <cluster-pid>

This method is also good if your app is launched with forever:

forever start cluster.js

Using with PM2

If you prefer PM2 you should use 'server.js' patch only. This will force PM2 to wait until active connections are closed when using:

pm2 reload <id>

With PM2 graceful reload don`t forget to set important process parameters:

• "instances": 0 - use cluster with multiple instances, so one instance will still work when another is reloaded.
• "kill_timeout": 5000 - wait more time to allow active connections finish their responses.