Load Profiles: Constant, Ramp, Spike, and Soak Tests

The four load test types

Each pattern is designed to answer a different question:

Pattern	Question answered
Smoke test	Does the app work at all under minimal load?
Load test	Does it meet SLOs at expected production load?
Stress / spike test	What happens at 2× or 10× normal load?
Soak test	Does it degrade over time under sustained load?

---

Smoke test

A quick sanity check — a handful of VUs for a short time.

export const options = {
  vus: 3,
  duration: '1m',
  thresholds: {
    http_req_failed: ['rate<0.01'],
  },
};

When to run: Every PR, before a deployment, after an incident.

---

Load test (constant rate)

Simulates steady-state production traffic.

export const options = {
  scenarios: {
    steady_load: {
      executor: 'constant-arrival-rate',
      rate: 500,          // 500 requests per second
      timeUnit: '1s',
      duration: '10m',
      preAllocatedVUs: 50,
    },
  },
  thresholds: {
    http_req_duration: ['p(95)<200'],
    http_req_failed:   ['rate<0.005'],
  },
};

Use constant-arrival-rate instead of constant-vus for meaningful throughput targets — VU-based tests produce variable RPS as latency changes.

---

Ramp-up test

Gradually increases load to find the breaking point.

export const options = {
  stages: [
    { duration: '2m', target: 100 },   // ramp to 100 VUs
    { duration: '5m', target: 100 },   // hold
    { duration: '2m', target: 500 },   // ramp to 500 VUs
    { duration: '5m', target: 500 },   // hold
    { duration: '2m', target: 1000 },  // ramp to 1000 VUs
    { duration: '5m', target: 1000 },  // hold
    { duration: '2m', target: 0 },     // ramp down
  ],
};

Watch the p99 latency chart. The point where it starts climbing steeply is your practical capacity.

---

Spike test

An instant jump to 10× normal load — simulates flash sales, news events, bot traffic.

export const options = {
  stages: [
    { duration: '30s', target: 50 },    // normal load
    { duration: '10s', target: 5000 },  // SPIKE
    { duration: '3m',  target: 5000 },  // hold the spike
    { duration: '10s', target: 50 },    // back to normal
    { duration: '3m',  target: 50 },    // recovery check
  ],
};

Key question: does the service recover after the spike, or does latency stay elevated?

---

Soak test

24–72 hours at moderate load. Catches memory leaks, connection pool exhaustion, disk fill.

export const options = {
  stages: [
    { duration: '5m',  target: 200 },
    { duration: '24h', target: 200 },  // hold for 24 hours
    { duration: '5m',  target: 0 },
  ],
  thresholds: {
    http_req_duration: ['p(99)<1000'],  // more lenient SLO for long runs
  },
};

Warning: Don't run soak tests against production unless you're certain about the load level.

---

Combining patterns

A complete test suite typically runs all four:

On every PR:    smoke test (3 VUs, 1 min)
Nightly:        load test  (steady production load, 15 min)
Pre-release:    stress test (ramp to 3× production, find breaking point)
Weekly:         soak test  (production load, 2 hours)

This covers correctness, SLO, capacity, and long-term stability in a single automated pipeline.