How to send more requests with variable payload size in K6?

This k6 script is designed for load testing an application by simulating multiple virtual users (VUs) that perform a series of HTTP requests. It includes setup for authentication, payload generation, and defines different testing scenarios.

Script Breakdown

• Imports and Setup: The script imports the http module for making HTTP requests and the check function for validating responses. It also imports a service_name function from an external module. The setup function is executed once before the main test runs. It sends a POST request to a token service to obtain an access token, checking that the response status is 200 (OK) and returning the token for use in subsequent requests.

export function setup() {
    const url = 'https://example-token-service.com/token';
    const formData = {};
    const loginRes = http.post(url, formData);
    check(loginRes, {
        'response code was 200': (res) => res.status === 200,
    });
    return { token: loginRes.json().access_token };
}

• Payload Generation: The script defines a target size for the payload (700 KB) and generates a JSON payload array using the generatePayloadArray function. This function constructs an array of empty objects until the total size reaches the specified target.

const targetSizeKB = 700;
const payload = generatePayloadArray(targetSizeKB);

• Scenarios Definition: Two scenarios are defined:

perVuIterations: 20 VUs, each performing 5000 iterations over a maximum duration of 300 seconds.
constantRequestRate: A constant rate of 248 requests per second for 300 seconds, with a maximum of 20 VUs.
const scenarios = {
    perVuIterations: {
        executor: 'per-vu-iterations',
        vus: 20,
        iterations: 5000,
        maxDuration: '300s',
    },
    constantRequestRate: {
        executor: 'constant-arrival-rate',
        rate: 248,
        timeUnit: '1s',
        duration: '300s',
        preAllocatedVUs: 20,
        maxVUs: 20,
    },
};

• Options Configuration: The script configures options for the test, including skipping TLS verification and selecting scenarios based on an environment variable.

export const options = {
    insecureSkipTLSVerify: true,
    scenarios: SCENARIO ? { [SCENARIO]: scenarios[SCENARIO] } : {},
};

• Main Function: The default function is executed by each VU, sending a POST request to the specified application endpoint using the token and payload generated earlier.

export default function (data) {
    const url = 'https://your-application-endpoint.com/_POST';
    service_name(url, data.token, payload);
}

• Payload Generation Function: The generatePayloadArray function constructs a JSON object containing an array of payloads, ensuring the total size matches the target size.

function generatePayloadArray(targetSizeKB) {
    const payloadArray = [];
    let currentSize = 0;

    while (currentSize < targetSizeKB * 1024) {
        const payload = {};
        const jsonString = JSON.stringify(payload);
        payloadArray.push(payload);
        currentSize += jsonString.length;
    }

    return JSON.stringify({ payload: payloadArray });
}

This script effectively sets up a load test that simulates user interactions with an application, allowing for performance evaluation under various conditions.
Complete Script as Follow:

import http from 'k6/http';
import { service_name } from './service.js';
import { check } from 'k6';

export function setup() {
    const url = 'https://example-token-service.com/token';
    const formData = {};
    const loginRes = http.post(url, formData);

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

    return { token: loginRes.json().access_token };
}

const targetSizeKB = 700;
const payload = generatePayloadArray(targetSizeKB);

const scenarios = {
    perVuIterations: {
        executor: 'per-vu-iterations',
        vus: 20,
        iterations: 5000,
        maxDuration: '300s',
    },
    constantRequestRate: {
        executor: 'constant-arrival-rate',
        rate: 248,
        timeUnit: '1s', // 248 iterations per second, i.e. 248 RPS
        duration: '300s',
        preAllocatedVUs: 20, // initial pool of VUs
        maxVUs: 20, // max VUs if preAllocatedVUs are not enough
    },
};

const { SCENARIO } = __ENV;

export const options = {
    insecureSkipTLSVerify: true,
    scenarios: SCENARIO ? { [SCENARIO]: scenarios[SCENARIO] } : {},
};

export default function (data) {
    const url = 'https://your-application-endpoint.com/_POST';
    service_name(url, data.token, payload);
}

function generatePayloadArray(targetSizeKB) {
    const payloadArray = [];
    let currentSize = 0;

    while (currentSize < targetSizeKB * 1024) {
        const payload = {};
        const jsonString = JSON.stringify(payload);
        payloadArray.push(payload);
        currentSize += jsonString.length;
    }

    return JSON.stringify({ payload: payloadArray });
}

• If you want to gradually increase the load, you can utilize the provided script, which implements a ramp-up strategy..

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

export let options = {
    stages: [
        { duration: '1m', target: 80 },
        { duration: '1m', target: 100 },
    ],
    insecureSkipTLSVerify: true,
};

export function setup() {
    const url = 'https://get-token-service.com/token';
    const res = http.post(url, {});
    return { token: res.json().access_token };
}

export default function ({ token }) {
    const url = 'https://example-server.com/_POST/api/endpoint';
    const headers = {
        'Authorization': token,
        'Content-Type': 'application/json',
    };
    const body = JSON.stringify({ payload: [] });

    const res = http.post(url, body, { headers });

    check(res, { 'status was 202': (r) => r.status === 202 });
}