Why Load Testing Matters
Your API works fine with 10 requests per second. But what about 1,000? Or 10,000? Load testing reveals how your API behaves under real-world traffic patterns.
Types of Load Tests
Baseline Test
Start with normal expected load and measure response times and throughput.
Ramp-up Test
Gradually increase load to find the breaking point.
Soak Test
Run at a fixed load for an extended period to detect memory leaks and resource exhaustion.
Spike Test
Suddenly increase load to see how the system recovers.
Stress Test
Push the system beyond its limits to see how it fails.
Key Metrics to Track
- Throughput - Requests per second
- Response Time - Time taken to get a response
- Error Rate - Percentage of failed requests
- CPU Usage - Server resource consumption
- Memory Usage - RAM consumption
- Database Connections - Active connections and pool saturation
Popular Load Testing Tools
JMeter (Free, On-premise)
- Developed by Apache Foundation
- Supports various protocols (HTTP, FTP, JDBC, SOAP)
- Strong GUI for scenario building
- Scalable with distributed testing
k6 (Modern, Cloud-native)
- Written in Go, very fast
- Uses JavaScript for test scripts
- Built-in cloud execution
- Great for API-first teams
Locust (Python-based)
- Write tests in Python
- Distributed testing built-in
- Web UI for monitoring
- Good for custom scenarios
Sample Load Test Script (k6)
import http from 'k6/http';
import { check, sleep } from 'k6';
export let options = {
vus: 100, // Virtual users
duration: '30s'
};
export default function () {
let res = http.get('https://api.example.com/users');
check(res, {
'status is 200': (r) => r.status === 200,
'response time < 500ms': (r) => r.timings.duration < 500,
});
sleep(1);
}Scaling Strategies
If your API fails under load:
- Horizontal Scaling - Add more servers
- Caching - Cache frequently accessed data
- Database Optimization - Optimize queries and indexes
- Rate Limiting - Protect against overload
- Async Processing - Move heavy work to background jobs
Conclusion
Load testing isn't optional—it's essential. Start with modest load tests during development, establish baseline metrics, and progressively increase load to find your limits. Regular load testing prevents surprises in production.