NodeJS Dynamic Cluster

NodeJS Dynamic Cluster is a way to manipulate your cluster size via a simple API, provided by this module. You will be able to resize the cluster with a simple curl localhost:8080/scale/X instead of relaunch your application.

This module uses the native cluster module, with just some pepper.

It is dependant on Debug only.

Please use the last version as the first (1.0.x and 1.1.x) use KoaJS.

Any help or hint will be appreciated.

NodeJS

Developed for the current LTS, 6.10.2.

API

This module exposes some API via HTTP to control the cluster.

/scale

Gives you the current size

curl localhost:8080/scale
> {"status":"ok","data":4}

/scale/:size

Scale the cluster to wanted :size, only if the new size is >0 and not equal to current size.

curl localhost:8080/scale/10
> {"status":"ok","data":10}

curl localhost:8080/scale/0
> {"status":"ok","data":10} # current size is returned

curl localhost:8080/scale/-20
> {"status":"ok","data":10} # current size is returned

/check

Returns info about the cluster' health. The health is OK if the current workers count equals the wanted cluster size.

curl localhost:8080/check
> {"status":"ok"}

Howto

Check example folder for a quick example.

const cluster = require('node-dynamic-cluster');

cluster(workerStart, [masterCallback], options);

workerStart

The function where your app code starts. A param with the worker id is passed to this callback by the main API.

function workerStart(id) {
  const debug = Debug('node-dynamic-cluster:test:' + id);

  http.createServer((req, res) => {
    debug(`Ops.. Someone poked me..`);
    res.end(`I'm ok, thanks. This is worker #${id} speaking`);
  }).listen(8080, '0.0.0.0', () => {
    debug(`listening on 8080`);
  });
}

masterCallback

not mandatory

Called after the listen() on the master is ready.

options

{
  clusterSize: 4,
  port: 8080,
  maxSize: 64,
  host: '0.0.0.0'
}

clusterSize

mandatory

How many workers to span up on boot. Defaulting to the number of CPU is a good choice.

const clusterSize = require('os').cpus().length

port

mandatory

The port the API will listen to.

maxSize

This avoid to destroy your server spanning 10 thousand workers... Not mandatory, defaults to 64. A warning will appear if you pass a value greater than 64. It is safe to ignore it, if you know what you are doing.

host

The host the API will listen to. Defaults to 0.0.0.0. Useful for securing your app.

debug

DEBUG=node-dynamic-cluster:*

# verbose
DEBUG=verbose:node-dynamic-cluster:*,node-dynamic-cluster:*.

test

npm test