Performance Testing and Load Testing ASP.NET Core APIs

Introduction

Before ShopNest flash sales, know your API limits — k6 load tests and BenchmarkDotNet micro-benchmarks reveal DB and CPU bottlenecks before customers do.

After this article you will

• Run k6 load scripts against ShopNest API
• Use BenchmarkDotNet for hot path code
• Profile with dotnet-counters and dotnet-trace
• Interpret latency percentiles (p95, p99)
• Optimize based on profiling evidence

Prerequisites

• Article 56 — Testing EF Core
• ShopNest Order Service / API from prior modules

Concept deep-dive

// k6 script — shopnest-load.js
import http from 'k6/http';
import { check, sleep } from 'k6';

export const options = {
  stages: [
    { duration: '1m', target: 50 },
    { duration: '3m', target: 200 },
    { duration: '1m', target: 0 },
  ],
  thresholds: { http_req_duration: ['p(95)<500'] },
};

export default function () {
  const res = http.get('https://api.shopnest.local/api/v1/products?page=1');
  check(res, { 'status 200': (r) => r.status === 200 });
  sleep(1);
}

// BenchmarkDotNet
[MemoryDiagnoser]
public class OrderTotalBenchmark
{
    [Benchmark]
    public decimal CalculateTotal() => OrderCalculator.Compute(_sampleLines);
}

Metrics: ASP.NET Core exposes requests/sec, active connections. Watch SQL CPU and connection pool exhaustion under load.

Hands-on — ShopNest Production API Optimization

1. k6 run against local ShopNest product list API.
2. Baseline p95 latency; add Redis cache; re-run and compare.
3. dotnet-counters monitor System.Runtime and Microsoft.AspNetCore.Hosting.
4. Document bottleneck (missing index vs no cache) and fix.

Common errors & best practices

• Load testing production without approval — use staging.
• Optimizing without measuring — guesswork wastes time.
• Ignoring connection pool limits under high concurrency.

Interview questions

Q: p95 latency?
A: 95% of requests faster than this value — SLA metric.

Q: k6 vs JMeter?
A: k6 scriptable in JS, developer-friendly; JMeter GUI-heavy.

Q: BenchmarkDotNet purpose?
A: Micro-benchmark C# methods with statistical rigor.

Summary

• Load test before major ShopNest launches
• k6 stages simulate ramp-up traffic realistically
• Profile first — cache and indexes fix most API slowness
• p95/p99 matter more than average latency

Previous: Testing EF Core
Next: Test-Driven Development

FAQ