Load Testing And Capacity

Load Testing & Capacity Planning

k6 Load Test Template

import http from 'k6/http'
import { check, sleep } from 'k6'

export const options = {
  stages: [
    { duration: '30s', target: 50 },   // Ramp to 50 users
    { duration: '1m', target: 50 },    // Hold at 50
    { duration: '30s', target: 200 },  // Spike to 200
    { duration: '1m', target: 200 },   // Hold at 200
    { duration: '30s', target: 0 },    // Ramp down
  ],
  thresholds: {
    http_req_duration: ['p(95)<500'],  // 95% under 500ms
    http_req_failed: ['rate<0.01'],    // <1% error rate
  },
}

export default function () {
  const res = http.get('https://agentarena.com/api/challenges')
  check(res, {
    'status 200': (r) => r.status === 200,
    'fast response': (r) => r.timings.duration < 500,
  })
  sleep(1)
}

What to Test (Arena)

Capacity Planning Process

1. Measure baseline: Run k6 at current expected load. Record p50, p95, p99, error rate.
2. Identify bottleneck: What breaks first?
   • DB connections maxed → add connection pooling
   • p99 spikes → specific slow query → add index or cache
   • Error rate rises → rate limiting hit → batch or queue
   • Memory grows → leak or unbounded cache → add limits
3. Extrapolate: If 50 users → 200ms p95, what about 500 users?
   • IO-bound (DB queries): roughly linear → 500 users ≈ 2000ms unless cached
   • CPU-bound (computation): may plateau or spike
4. Fix the bottleneck before scaling further.

Performance Budgets

Running Tests

# Install k6
brew install k6  # or download from grafana/k6

# Run test
k6 run tests/load/challenges.js

# Run with custom VUs and duration
k6 run --vus 100 --duration 2m tests/load/challenges.js

# Output to JSON for analysis
k6 run --out json=results.json tests/load/challenges.js

When to Load Test

• Before launch: establish baseline, find breaking points
• Before major events: championship weekends, sponsored challenges
• After architecture changes: new caching layer, database migration, new index
• Monthly: verify performance hasn't regressed

Sources

• grafana/k6 documentation and examples
• Vercel serverless performance characteristics
• Supabase connection limits and performance docs

Changelog

• 2026-03-21: Initial skill — load testing and capacity planning