hashring

Hash ring provides consistent hashing based on the libketema library.

Installation

You can either install it using the Node Package Manager (NPM)

npm install hashring

Or fork this repository to your machine

git clone git://github.com/3rd-Eden/node-hashring.git hashring

Basic usage

The constructor is designed to handle multiple arguments types as the hash ring can be used for different use cases. You have the ability to use a String to add a single server, a Array to provide multiple servers or an Object to provide servers with a custom weight. The weight can be used to give a server a bigger distribution in the hash ring. For example you have 3 machines, 2 of those machines have 8 gig memory and one has 32 gig of memory because the last server has more memory you might it to handle more keys than the other server. So you can give it a weight of 2 and the other servers a weight of 1.

Creating a hash ring with only one server

var hashring = require('hashring');
var ring = new hashring('192.168.0.102:11212');

Creating a hash ring with multiple servers

var hashring = require('hashring');
var ring = new hashring([ '192.168.0.102:11212', '192.168.0.103:11212', '192.168.0.104:11212']);

Creating a hash ring with multiple servers and weights

var hashring = require('hashring');
var ring = new hashring({
  '192.168.0.102:11212': 1
, '192.168.0.103:11212': 2
, '192.168.0.104:11212': 1
});

By default the hash ring uses a JavaScript crc32 implementation hashing algorithm. But this can be overwritten by adding a second argument to the constructor. This can be anything that is supported as hashing algorithm by the crypto module.

var hashring = require('hashring');
var ring = new hashring('192.168.0.102:11212', 'md5');

I have chosen crc32 as default algorithm because a creates a nice dense ring distribution. Another good alternative and common used hashing algorithm is md5. The JavaScript crc32 algorithm is faster than md5. So If you are doing allot of operations per seconds these small differences can really matter.

Small API

In these examples I assume that you already setup a hashring instance, with the variable name ring like I did the in the examples illustrated above.

Getting a node by key a.k.a key -> node look up, this is where all the magic is happening.

ring.getNode('foo'); // => '192.168.0.104:11212'
ring.getNode('pewpew'); // => '192.168.0.103:11212'

Replacing a server If you are experiencing downtime with one of your servers, you might want to hot swap with a new server.

ring.replaceServer('192.168.0.104:11212','192.168.0.112:11212');
ring.getNode('foo'); // => '192.168.0.112:11212'

Add a server Adds a new server to the hash ring, but please note that this could cause a shift in current key -> server distribution.

ring.addServer('192.168.0.102:11212');

Remove a server Remove a server from the generated hash ring.

ring.removeServer('192.168.0.102:11212');

For a more extensive documentation: http://3rd-eden.github.com/node-hashring/