hashring

What is hashring?

The hashring npm package is a consistent hashing library that allows for the distribution of keys across a set of nodes. It is useful for load balancing, distributed caching, and sharding data across multiple servers.

What are hashring's main functionalities?

Creating a Hash Ring

This feature allows you to create a hash ring with a set of nodes. The nodes can be any identifier, such as server names or IP addresses.

const HashRing = require('hashring');
const ring = new HashRing(['node1', 'node2', 'node3']);

Adding and Removing Nodes

This feature allows you to dynamically add or remove nodes from the hash ring. This is useful for scaling up or down the number of nodes in your system.

ring.add('node4');
ring.remove('node2');

Getting the Node for a Key

This feature allows you to get the node responsible for a given key. This is useful for determining which node should handle a particular piece of data.

const node = ring.get('myKey');

Weighting Nodes

This feature allows you to assign weights to nodes, so some nodes can handle more keys than others. This is useful for load balancing when some nodes have more capacity than others.

const weightedRing = new HashRing({'node1': 1, 'node2': 2, 'node3': 1});

Other packages similar to hashring

consistent-hashing

The consistent-hashing package provides similar functionality for consistent hashing. It allows for the distribution of keys across a set of nodes and supports adding and removing nodes dynamically. Compared to hashring, it is simpler and may have fewer features, but it is still effective for basic consistent hashing needs.

README

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
});

Creating a hash ring with multiple servers an vnodes selected per nodes

var hashring = require('hashring');

var ring = new hashring({
  '192.168.0.102:11212': {"vnodes": 5}
, '192.168.0.103:11212': {"vnodes": 10}
, '192.168.0.104:11212': {"vnodes": 7}
});

Optionaly you could add the weigth property to the object.

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.get('foo'); // => '192.168.0.104:11212'
ring.get('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.replace('192.168.0.104:11212','192.168.0.112:11212');
ring.get('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.add('192.168.0.102:11212');

Remove a server

Remove a server from the generated hash ring.

ring.remove('192.168.0.102:11212');

Creating a range

Iterates over the nodes for a give key, can be used to create redundancy support.

ring.range('key', 3);

Ending

Clean up the internal hash ring, kill the cache, kill nodes, nuke the planet.

range.end();

For a more extensive documentation: Read the source, it's not rocket sience.