Load balancing between workers in Node.js - Performance & Optimization

Performance: Load balancing between workers

HIGH IMPACT

This affects how efficiently the server handles incoming requests and distributes CPU work, impacting response time and throughput.

Distributing incoming HTTP requests across multiple Node.js worker processes

Node.js

const cluster = require('cluster');
const http = require('http');
const numCPUs = require('os').cpus().length;

if (cluster.isMaster) {
  cluster.schedulingPolicy = cluster.SCHED_RR;
  for (let i = 0; i < numCPUs; i++) {
    cluster.fork();
  }
  cluster.on('exit', (worker) => {
    cluster.fork(); // replace dead worker
  });
} else {
  http.createServer((req, res) => {
    // handle request
    res.end(`Handled by worker ${process.pid}`);
  }).listen(8000);
}

Using cluster module with multiple workers and round-robin scheduling allows Node.js to distribute load across CPU cores evenly, improving concurrency.

📈 Performance GainReduces request queuing and balances CPU load, lowering INP and improving throughput.

Distributing incoming HTTP requests across multiple Node.js worker processes

Node.js

const cluster = require('cluster');
if (cluster.isMaster) {
  cluster.schedulingPolicy = cluster.SCHED_NONE;
  cluster.fork();
  cluster.fork();
} else {
  require('http').createServer((req, res) => {
    // handle request
    res.end('Handled by worker');
  }).listen(8000);
}

Master process does not balance load; OS assigns requests unevenly causing some workers to be overloaded while others idle.

📉 Performance CostCauses uneven CPU usage and request queuing, increasing average response time and INP.

Performance Comparison

Pattern	CPU Utilization	Request Queuing	Response Time	Verdict
Single worker or unbalanced cluster	Low to uneven	High under load	High latency	[X] Bad
Balanced cluster with multiple workers	High and even	Low	Low latency	[OK] Good

Rendering Pipeline

Load balancing affects the server-side event loop and CPU scheduling, which impacts how quickly requests are processed and responses sent.

→Event Loop

→CPU Scheduling

→Network I/O

⚠️ BottleneckUneven worker load causes some event loops to block longer, delaying response generation.

Core Web Vital Affected

INP

This affects how efficiently the server handles incoming requests and distributes CPU work, impacting response time and throughput.

Optimization Tips

1Use one worker per CPU core for best CPU utilization.

2Restart workers automatically if they crash to maintain availability.

3Avoid single-threaded bottlenecks by distributing requests evenly.

Performance Quiz - 3 Questions

What is the main performance benefit of using multiple Node.js workers with load balancing?

A Improves CPU utilization and reduces request latency

B Reduces memory usage per request

C Eliminates the need for asynchronous code

D Increases the size of the server bundle

DevTools: Performance

How to check: Record a CPU profile while sending concurrent requests; check CPU usage distribution and event loop delays per worker.

What to look for: Balanced CPU usage across workers and minimal event loop blocking indicate good load balancing.