readme.md

loadbalance

This is a collection of load balancing engines in (what is hopefully) their most distilled form.

The goal was to create a highly reusable implementation that imposes as little as possible on the user.

Install

With npm do:

npm i loadbalance

const loadbalance = require('loadbalance')

Usage

To use, instantiate an engine or call a factory method with a pool. Then call pick(), which will return the selected object, calling pick() repeatedly will yield the same or a different object from the pool, depending on the algorithm which powers that engine.

const loadbalance = require('loadbalance')
const engine = loadbalance.random(['a', 'b', 'c'])
const pick = engine.pick()

pick()

pick() is called without any arguments and will always return an object which is a member of the pool according to the pool's selection strategy

Engines

Random Engine

The random engine picks an object from the pool at random, each time pick() is called.

const loadbalance = require('loadbalance')
const engine = loadbalance.random(['a', 'b', 'c'])
const pick = engine.pick()

new RandomEngine(pool, seed)

const engine = new loadbalance.RandomEngine(pool)

Pool - an objects to pick from, eg [1,2,3] Seed - an optional seed that will be used to recreate a random sequence of selections

Weighted Random Engine

The random engine picks an object from the pool at random but with bias (probably should have called it BiasedRandomEngine), each time pick() is called.

const loadbalance = require('loadbalance')
const engine = loadbalance.random([
    { object: 'a', weight: 2 }, 
    { object: 'b', weight: 3 }, 
    { object: 'c', weight: 5 }
])
const pick = engine.pick()

With this engine, calling pick() repeatedly will roughly return 'a' 20% of the time, 'b' 30% of the time and 'c' 50% of the time

new WeightedRandomEngine(pool, seed)

const engine = new loadbalance.WeightedRandomEngine(pool)

Pool - objects to pick from. Each object is of the form:

const object1 = {
    object: 'something',
    weight: 2
}

Seed - an optional seed that will be used to recreate a random sequence of selections

RoundRobinEngine

An engine that picks objects from its pool using Round Robin algorithm (doh!)

const loadbalance = require('loadbalance')
const engine = loadbalance.roundRobin(['a', 'b', 'c'])
const pick = engine.pick()

The roundRobin() factory method can be used to obtain both RoundRobinEngine and WeightedRoundRobinEngine. The decision is based on the contents of the pool.

new RoundRobinEngine(pool)

const engine = new loadbalance.RoundRobinEngine(pool)

Pool - objects to pick from, eg [1,2,3]

WeightedRoundRobinEngine

Same as round robin engine, only members of the pool can have weights.

const loadbalance = require('loadbalance')
const engine = loadbalance.roundRobin([{ object: 'a', weight: 2 }, {object: 'b', weight: 1 }])
const pick = engine.pick()

call pick six times using the above engine will yield: 'a', 'a', 'b', 'a', 'a', 'b'

new WeightedRoundRobinEngine(pool)

const engine = new loadbalance.WeightedRoundRobinEngine(pool)

Pool - objects to pick from. Each object is of the form:

const object1 = {
    object: 'something',
    weight: 2
}

Weight should always be an integer which is greater than zero. Object (you can also use value, its an alias property) can be anything you want, just like other pools. It cannot, however, be null or undefined at the time the pool is created.

PriorityEngine

Not yet implemented

Extensibility

Here is an example of a custom engine:

const AbstractEngine = require('loadbalance').AbstractEngine

class MyEngine extends AbstractEngine {
    constructor(pool) {
        super(pool)
    }

    _pick(pool) {
        // pick something from the pool somehow and return it
    }
}

misc

This module shares some functinality with pool module. It is worth taking a look at it if you are looking for something more high level.

This module is heavily inspired by this article about load balance algorithms

license

MIT © yaniv kessler