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throng

Throng

Dead-simple one-liner for clustered Node.js apps.

Runs X workers and respawns them if they go down. Correctly handles signals from the OS.

const throng = require('throng');
 
throng((id) => {
  console.log(`Started worker ${id}`);
});
$ node example
Started worker 1
Started worker 2
Started worker 3
Started worker 4

Installation

npm install --save throng

For older versions of node (< 4.x), use throng 2.x.

Use

Simplest; automatically fork 1 worker per CPU core:

throng(startFunction);

Specify a number of workers:

throng(3, startFunction);

Specify more options:

throng({
  workers: 16,
  grace: 1000,
  master: masterFunction,
  start: startFunction
});

Handle signals (for cleanup on a kill signal, for instance):

throng((id) => {
  console.log(`Started worker ${id}`);
 
  process.on('SIGTERM', function() {
    console.log(`Worker ${id} exiting`);
    console.log('Cleanup here');
    process.exit();
  });
});

All Options (with defaults)

throng({
  workers: 4,       // Number of workers (cpu count) 
  lifetime: 10000,  // ms to keep cluster alive (Infinity) 
  grace: 4000       // ms grace period after worker SIGTERM (5000) 
}, startFn);

A Complex example

const throng = require('./lib/throng');
 
throng({
  workers: 4,
  master: startMaster,
  start: startWorker
});
 
// This will only be called once 
function startMaster() {
  console.log(`Started master`);
}
 
// This will be called four times 
function startWorker(id) {
  console.log(`Started worker ${ id }`);
 
  process.on('SIGTERM', () => {
    console.log(`Worker ${ id } exiting...`);
    console.log('(cleanup would happen here)');
    process.exit();
  });
}
$ node example-complex.js
Started master
Started worker 1
Started worker 2
Started worker 3
Started worker 4
 
$ killall node
 
Worker 3 exiting...
Worker 4 exiting...
(cleanup would happen here)
(cleanup would happen here)
Worker 2 exiting...
(cleanup would happen here)
Worker 1 exiting...
(cleanup would happen here)

Tests

npm test