API Performance & Load Testing

// Good performance targets:
p50:  < 100ms  (median user sees sub-100ms)
p95:  < 200ms  (95% of users happy)
p99:  < 500ms  (99% acceptable)
p99.9: < 1s    (even worst case under 1 second)

// Don't just look at averages!
// Average: 150ms might hide some 5s requests

// Install: brew install k6 (or download binary)
// Run: k6 run script.js

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

export let options = {
  vus: 100,              // 100 virtual users
  duration: '5m',        // Run for 5 minutes
};

export default function() {
  http.get('https://api.example.com/users');
  sleep(1);
}

// Output shows real-time metrics:
// http_req_duration: avg=95ms p95=150ms
// http_req_failed: 0.05%
// iterations: 28,500

# Install: npm install -g artillery
# Run: artillery run loadtest.yml

# loadtest.yml
config:
  target: "https://api.example.com"
  phases:
    - duration: 60
      arrivalRate: 10    # 10 users per second
    - duration: 120
      arrivalRate: 50    # Ramp to 50/second
      
scenarios:
  - name: "Get users"
    flow:
      - get:
          url: "/users"
      - think: 2          # Wait 2 seconds
      - get:
          url: "/users/{{ $randomNumber(1, 1000) }}"

# Artillery outputs summary with response times and errors

# Install: pip install locust
# Run: locust -f locustfile.py

from locust import HttpUser, task, between

class APIUser(HttpUser):
    wait_time = between(1, 3)  # Wait 1-3s between requests
    
    @task(3)  # 3x more likely than other tasks
    def get_users(self):
        self.client.get("/users")
    
    @task(1)
    def get_user(self):
        self.client.get("/users/123")
    
    @task(2)
    def create_user(self):
        self.client.post("/users", json={
            "name": "Test User",
            "email": "[email protected]"
        })

# Open http://localhost:8089 to control test and see real-time stats

// Realistic user journey
export default function() {
  // 1. Browse products
  http.get('/products');
  sleep(2);  // User reads page
  
  // 2. View product detail
  http.get('/products/123');
  sleep(5);  // User reads details
  
  // 3. Add to cart
  http.post('/cart', { product_id: 123, qty: 1 });
  sleep(1);
  
  // 4. Checkout (10% of users)
  if (Math.random() < 0.1) {
    http.post('/checkout', {...});
  }
}

// k6 thresholds - fail test if not met
export let options = {
  thresholds: {
    'http_req_duration': ['p(95)<200'],     // 95% under 200ms
    'http_req_duration{endpoint:search}': ['p(95)<500'],  // Search can be slower
    'http_req_failed': ['rate<0.01'],       // < 1% errors
    'http_reqs': ['rate>100'],              // > 100 req/s throughput
  },
};

// Test fails if any threshold not met