Load tests development for website (k6)

Load Testing Development for Websites (k6)

k6 is a modern load testing tool from Grafana Labs. Scenarios in JavaScript, built-in metrics, integration with Grafana/InfluxDB. Optimal for API load testing and performance SLA verification.

Installation

# Windows
winget install k6

# macOS
brew install k6

# Linux
sudo apt install k6

Basic Scenario

// scripts/smoke-test.js
import http from 'k6/http';
import { check, sleep } from 'k6';
import { Rate } from 'k6/metrics';

const errorRate = new Rate('error_rate');

export const options = {
    vus: 10,           // 10 virtual users
    duration: '30s',   // for 30 seconds

    thresholds: {
        http_req_duration: ['p(95)<500'],  // 95% of requests faster than 500ms
        http_req_failed:   ['rate<0.01'],  // less than 1% errors
        error_rate:        ['rate<0.05'],
    },
};

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

    const ok = check(res, {
        'status is 200':        r => r.status === 200,
        'response time < 500ms': r => r.timings.duration < 500,
        'has data array':        r => r.json('data') !== undefined,
    });

    errorRate.add(!ok);
    sleep(1);
}

Ramping Scenario (Increasing Load)

export const options = {
    stages: [
        { duration: '2m', target: 10 },   // ramp-up: 0→10 VU for 2 minutes
        { duration: '5m', target: 10 },   // stay: 10 VU for 5 minutes
        { duration: '2m', target: 50 },   // ramp-up to 50 VU
        { duration: '5m', target: 50 },   // stay: 50 VU for 5 minutes
        { duration: '2m', target: 100 },  // peak load
        { duration: '5m', target: 100 },
        { duration: '2m', target: 0 },    // ramp-down
    ],
    thresholds: {
        http_req_duration: ['p(99)<2000'],
        http_req_failed:   ['rate<0.02'],
    },
};

Scenario with Authorization

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

// Load test users from file
const users = new SharedArray('users', () =>
    JSON.parse(open('./data/users.json'))
);

export default function () {
    const user = users[Math.floor(Math.random() * users.length)];

    // Login
    let loginRes;
    group('Login', () => {
        loginRes = http.post('https://staging.example.com/api/auth/login',
            JSON.stringify({ email: user.email, password: user.password }),
            { headers: { 'Content-Type': 'application/json' } }
        );

        check(loginRes, {
            'login successful': r => r.status === 200,
            'token received':   r => r.json('access_token') !== undefined,
        });
    });

    const token = loginRes.json('access_token');
    const headers = { Authorization: `Bearer ${token}` };

    sleep(1);

    // Browse Products
    group('Browse Products', () => {
        const res = http.get('https://staging.example.com/api/products?page=1', { headers });
        check(res, { 'products loaded': r => r.status === 200 });
        sleep(2);
    });

    // Create Order
    group('Create Order', () => {
        const res = http.post('https://staging.example.com/api/orders',
            JSON.stringify({ product_id: 1, quantity: 1 }),
            { headers: { ...headers, 'Content-Type': 'application/json' } }
        );
        check(res, { 'order created': r => r.status === 201 });
    });

    sleep(1);
}

Sending Metrics to Grafana

# InfluxDB + Grafana
k6 run --out influxdb=http://localhost:8086/k6 script.js

# k6 Cloud
k6 cloud script.js

# Grafana Cloud k6
K6_CLOUD_TOKEN=xxx k6 run --out cloud script.js

Interpreting Results

Results show key metrics: http_req_duration (response time), http_req_failed (error rate), custom metrics like error_rate. Pass/fail is determined by thresholds defined in options.

Implementation Timeline

Basic set of load testing scenarios (smoke, load, stress, soak): 3–5 days.