Load test

Reliability and performance tests

1 min

Intro

Load test simulates expected user traffic to measure the performance of a system under normal conditions. It ensures that the system can handle concurrent users and transactions within acceptable performance thresholds.

Easy explanation

Checking if a bridge can safely carry the daily traffic of cars over time.

Scheme

Load test scheme

Info

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

Key characteristics

Focused on expected load: Simulates real-life usage scenarios with many users.
Sustained execution: Runs over a longer period to gather performance metrics.
Concurrent users: Measures how the system handles simultaneous user sessions.
Performance benchmarks: Helps define acceptable response times, throughput, and error rates.
Detects bottlenecks: Reveals performance limitations under typical usage.

Practical examples

Can 1000 users browse the shop at the same time?
How fast does the API respond when 500 concurrent users call it?

Users and time

Number of virtual users:

Depends on the expected traffic. Example: simulate 100–1000 concurrent users.
Execution time:

Usually between 10-60 minutes (or longer), long enough to measure system behavior under sustained load.

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 100 users
    { duration: '3m', target: 100 },
    // hold 100 users for 30m
    { duration: '30m', target: 100 },
    // 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);
}

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