wrr

A tiny (148B) weighted round robin utility

At its core, a "weighted round robin" (wrr) will skew a list's random selection towards list items that have more weight given to them.This is generally seen in load-balancing contexts, but wrr is not at all limited to that scenario.

From the NGINX glossary:

Weighted round robin – A weight is assigned to each server based on criteria chosen by the site administrator; the most commonly used criterion is the server’s traffic‑handling capacity. The higher the weight, the larger the proportion of client requests the server receives. If, for example, server A is assigned a weight of 3 and server B a weight of 1, the load balancer forwards 3 requests to server A for each 1 it sends to server B.

This module exposes three module definitions:

• ES Module: dist/wrr.mjs
• CommonJS: dist/wrr.js
• UMD: dist/wrr.min.js

Install

$ npm install --save wrr

Usage

Related to the NGINX example above

import wrr from 'wrr';

const servers = [
	// 3x capacity of B; picked 3x more often than B
	{ item: 'Server A', weight: 3 },
	// our "base unit" for comparison
	{ item: 'Server B', weight: 1 },
	// 2x capacity of B; picked 2x more often than B
	{ item: 'Server C', weight: 2 },
];

// Create reusable instance
const toPickServer = wrr(servers);

toPickServer(); //=> 'Server A'
toPickServer(); //=> 'Server C'
toPickServer(); //=> 'Server A'
toPickServer(); //=> 'Server A'
toPickServer(); //=> 'Server A'
toPickServer(); //=> 'Server A'
toPickServer(); //=> 'Server C'
toPickServer(); //=> 'Server A'
toPickServer(); //=> 'Server A'
toPickServer(); //=> 'Server B'
toPickServer(); //=> 'Server C'
toPickServer(); //=> 'Server A'

API

wrr(items)

Returns: Function

Returns the function that should be used to select from your items.You should only call wrr when your items change.

items

Type: Array

The candidates for selection, each of which must be an object of Weighted shape:

interface Weighted<T> {
	/** The item's weight (non-decimal) */
	weight: number;
	/** The array item */
	item: T;
}

You can use any rubric for your weight value; however, only whole-number integers are allowed.

The item key can hold any value you'd like. This is what's returned to you directly.

License

MIT © Luke Edwards