Stress test

Reliability and performance tests

1 min

Intro

Stress test evaluates how a system performs under extreme but sustained conditions that exceed normal operational capacity. The goal is to observe performance degradation and system behavior under heavy load — not necessarily to cause failure.

Easy explanation

Checking how a bridge behaves when overloaded with more cars than usual.

Scheme

Stress test scheme

Info

To better understand the terms in testing and tool k6 see vocabulary.

Key characteristics

Simulates extreme conditions: Load well above expected peak traffic.
Sustained stress: Holds the system at high load to observe performance degradation.
Degradation focus: Measures response times, errors, and stability under stress.
Recovery observation: Checks whether the system can return to normal performance after removing stress.
Capacity planning: Helps determine safe operational limits and buffer capacity.

Practical examples

How does the system perform when subjected to 1.5x or 2x peak traffic for an hour?
Does the application slow down gracefully or fail suddenly under heavy stress?

Users and time

Number of virtual users:

Simulates load above the expected. Example: if load is 500 users - test with 750–1000 users (1,5-2x of the load).
Execution time:

Typically 10 min to 1 h, long enough to observe behavior under prolonged stress.

Examples with tool k6

Simple example

script.js

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

export const options = {
  stages: [
    // approx. 10% of duration, ramp-up to 1,5-2x of the load users
    { duration: '3m', target: 150 },
    // hold 150 users for 30m
    { duration: '30m', target: 150 },
    // approx. 10% of duration, ramp-down to 0 users
    { duration: '3m', target: 0 },
  ],
  thresholds: {
    http_req_failed: ['rate<0.01'], // <1% errors
    http_req_duration: ['p(95)<1000'], // 95% of requests < 1s
  },
};

export default function () {
  const response = http.get('https://api.example.com/products');

  check(response, {
    'status is 200': (res) => res.status === 200,
  });

  sleep(1);
}

Deep dive handbook