Load Testing Bun Apps

🚀 Introduction to Load Testing Bun Apps

Bun is known for its blazing-fast performance and tight bundling of key JavaScript tooling like a bundler, test runner, and package manager. But as you scale your application, one question becomes crucial — can your Bun app handle real-world traffic under pressure? That’s where load testing enters the scene.

In this guide, we’ll walk through how to conduct proper load testing on Bun-powered applications, using tools like Artillery and k6 to simulate real-world traffic, check for bottlenecks, and optimize performance 🚦.

🧠 Why Load Testing Matters for Bun Apps

Load testing is more than just throwing requests at your app. It's about understanding how your backend behaves under high user load, spike traffic, or concurrent requests. Here’s why it’s important for Bun-based projects:

• Identify bottlenecks before real users do
• Evaluate server limits like CPU, memory, and I/O
• Ensure consistent response times under stress
• Improve scalability by tuning configurations

🛠️ Setting Up a Simple Bun Server

Let’s start with a basic Bun server to test:

const server = Bun.serve({
  port: 3000,
  fetch(req) {
    return new Response("Hello from Bun 🚀");
  },
});

console.log("Server is running on http://localhost:3000");

Save this file as index.ts and run it using:

bun index.ts

📊 Load Testing with Artillery

Artillery is a great tool for HTTP-based load testing. Install it globally:

npm install -g artillery

Create a file named load-test.yml:

config:
  target: "http://localhost:3000"
  phases:
    - duration: 30
      arrivalRate: 50

scenarios:
  - flow:
      - get:
          url: "/"

Run the test using:

artillery run load-test.yml

This setup simulates 50 users per second for 30 seconds. You’ll get a detailed report showing request rates, response times, and error percentages.

📈 Load Testing with k6 (Script-Based)

If you prefer scriptable load testing, k6 is an awesome option. Install it:

brew install k6   # macOS
choco install k6  # Windows

Now write a test file test.js:

import http from 'k6/http';
import { sleep } from 'k6';

export let options = {
  vus: 100,
  duration: '30s',
};

export default function () {
  http.get('http://localhost:3000');
  sleep(1);
}

Execute the test:

k6 run test.js

This spins up 100 virtual users for 30 seconds, slamming your Bun app with GET requests.

⚙️ Tips to Improve Bun App Performance

• Use Bun's native primitives like Bun.serve() for faster I/O.
• Avoid blocking code that might freeze the event loop.
• Use caching for repeated operations.
• Bundle assets smartly with Bun’s built-in bundler.

📁 Sample Output Snapshot (Artillery)

Scenarios launched:  1500
Scenarios completed: 1500
Requests completed:  1500
RPS sent: 50.04
Request latency:
  min: 5.2 ms
  max: 45.3 ms
  median: 8.1 ms
  p95: 13.4 ms
  p99: 18.6 ms

Numbers like these help you assess if your Bun app can withstand real-world traffic, and where optimizations are necessary.

🔍 Monitoring During Load Tests

During intense testing, monitor CPU and memory usage using tools like:

• htop – for system-level stats
• bun inspect – to analyze Bun’s memory use (coming soon in stable)
• netstat – to monitor open connections

🧠 Final Thoughts on Load Testing with Bun

Bun is powerful, but to build production-grade apps, you need to ensure it can handle the stress. Load testing helps validate performance, uncover hidden bugs, and ensure uptime under pressure. Whether you’re building a REST API, a WebSocket server, or a full-stack app with Bun, testing under load is non-negotiable.

Embrace testing early — and let Bun show off its real power under fire! 🔥