Skip to main content

​
Overview

The LoadBalancer class is the central component of the HTTP load balancer. It coordinates between the backend pool and the load balancing strategy to select the optimal backend server for each incoming request.

​
Constructor

Creates a new LoadBalancer instance with the specified backend pool and load balancing strategy. 
constructor(
  backendPool: BackendPool,
  strategy: RoundRobin
)
​
backendPool
BackendPool
required
The pool of backend servers to distribute requests across. Maintains the health status of all backends.
​
strategy
RoundRobin
required
The load balancing strategy to use for selecting backends. Currently supports round-robin distribution.

​
Methods

​
pickBackend()

Selects the next healthy backend server to handle an incoming request based on the configured strategy. 
pickBackend(): Backend
Returns: Backend - The selected backend server object containing url and health properties. Throws: Error if no healthy backends are available. Behavior:
  • Retrieves all healthy backends from the backend pool
  • Delegates selection to the configured strategy (e.g., round-robin)
  • Returns a Backend object with the selected server’s URL and health status

​
Usage examples

​
Basic setup

import { LoadBalancer } from './balancer/loadBalancer';
import { BackendPool } from './balancer/pool';
import { RoundRobin } from './balancer/roundRobin';

// Create backend pool with server URLs
const pool = new BackendPool([
  'http://localhost:3001',
  'http://localhost:3002',
  'http://localhost:3003'
]);

// Initialize load balancing strategy
const strategy = new RoundRobin();

// Create load balancer
const loadBalancer = new LoadBalancer(pool, strategy);

​
Selecting a backend

try {
  const backend = loadBalancer.pickBackend();
  console.log(`Selected backend: ${backend.url}`);
  // Forward request to backend.url
} catch (error) {
  console.error('No healthy backends available');
  // Return 503 Service Unavailable
}

​
Integration with proxy handler

import express from 'express';
import { ProxyHandler } from './proxy/proxyHandler';

const app = express();

// Use load balancer with proxy handler
app.use('*', ProxyHandler(loadBalancer, pool));

app.listen(8080, () => {
  console.log('Load balancer running on port 8080');
});

Build docs developers (and LLMs) love

Get started for freeTalk to us