sticky-cluster

sticky-cluster

What is it

In cluster environment socket.io requires you to use sticky sessions, to ensure that a given client hits the same process every time, otherwise its handshake mechanism won't work properly. To accomplish that, manuals suggest the sticky-session module.

My module is based on the same principles as sticky-session, but utilizes a more efficient hash function and also works asynchronously out of the box.

Advantages

• up to 10x faster than sticky-session
• much better scattering over the worker processes than that of sticky-session
• asynchronous out of the box, just run a callback when you're done initializing everything else
• works correctly with ipv6

More alternatives

• sticky-session -- worse perfomance, not async
• throng -- plain cluster, not sticky
• node-cluster-socket.io -- doesn't work with ipv6

Get started

As usual

npm install sticky-cluster --save

then

require('sticky-cluster')(

  // server initialization function
  function (callback) {
    var http = require('http');
    var app = require('express')();
    var server = http.createServer(app);
      
    // configure an app
      // do some async stuff if needed
      
    // don't do server.listen(), just pass the server instance into the callback
    callback(server);
  },
  
  // options
  {
    concurrency: 10,
    port: 3000,
    debug: true,
    env: function (index) { return { stickycluster_worker_index: index }; }
  }
);

Accepted options

Here's the full list of accepted options:

key	meaning	default
concurrency	number of workers to be forked	number of CPUs on the host system
port	http port number to listen	8080
debug	log actions to console	false
prefix	prefix in names of IPC messages	sticky-cluster:
env	function (workerIndex => workerEnv) to provide additional worker configuration through the environment variables	sets stickycluster_worker_index (be aware that worker's index stays the same through its death and resurrection, but worker's id, which is used in debug messages, changes)
hardShutdownDelay	delay(ms) to trigger the hard shutdown if the graceful shutdown doesn't complete	60 * 1000 ms
errorHandler	callback function for the net.Server.error event on the serverInstance created in master.js.	function (err) { console.log(err); process.exit(1); }

Example

Open terminal at the ./example directory and sequentially run npm install and npm start. Navigate to http://localhost:8080. Have a look at the source.

Benchmarking

There's a script you can run to test various hashing functions. It generates a bunch of random IP addresses (both v4 and v6) and then hashes them using different algorithms aiming to get a consistent {IP address -> array index} mapping.

For every hash function the script outputs execution time in milliseconds (less is better) and distribution of IP addresses over the clients' ids (more even distribution is better).

$ cd ./benchmark
$ npm install
$ npm start -- <num_workers> <num_ip_addresses>

An output from my laptop:

$ npm start
generating random ips...
benchmarking...
int31
  time (ms):  188
  scatter:  [ 25788, 8378, 7768, 9438, 7280, 6649, 9648, 8061, 10287, 6703 ]
djb2
  time (ms):  20
  scatter:  [ 9957, 9809, 9853, 10075, 10077, 9957, 9982, 10068, 10179, 10043 ]

The algorithm used in the sticky-session module is int31 and the local one is djb2. As might be seen, the djb2 algorithm provides significant time advantage and clearly more even scattering over the worker processes.

Changelog

0.3.2 -> 0.3.3

• Allow the caller to specify a callback function for the net.Server.error event on the serverInstance created in master.js.

0.3.1 -> 0.3.2

• Close alive connections before exiting to achieve graceful shutdown.
• Add hardShutdownDelay option to trigger hard shutdown if the graceful shutdown doesn't complete in the amount of delay.

0.2.1 -> 0.3.0

• Allow to set individual worker environment variables through the options.env function.

0.2.0 -> 0.2.1

• Handle empty IP addresses.

0.1.2 -> 0.2.0

• Removed a SIGTERM listener on the master process.
• Replaced .on('SIGINT', ...) with .once('SIGINT', ...).
• Improved debug logs.
• Moved unnecessary dependencies from the main package to the ./example and ./benchmark apps.
• Fixed a few minor issues in the mentioned apps.

0.1.1 -> 0.1.2

• Updated the example.

0.1.0 -> 0.1.1

• Published to NPM.