API load test with K6 (JavaScript + Go)

Lately while learning load test frameworks alternative to Locust (Python), I found K6 framework (https://k6.io/) which is really amazing and quick to work with.

To install: https://docs.k6.io/docs/installation

What I love the most about K6 is it allows to script with JavaScript which I am familiar with (I am using Jest + Axios to test API). Although there are some limits like I cannot use `npm install` and import node_modules like with nodejs but I can work around with bundling those modules (https://docs.k6.io/docs/modules).

And the core of K6 is Go so the speed of the same test run compared with Locust is quite faster according to my test.

Below is a sample script to test with a signUp API.

import config from '../common/config.js' // I use config.js to export API endpoint variables
import http from 'k6/http'
import { check, sleep } from 'k6'
import { Trend } from 'k6/metrics'
import faker from 'cdnjs.com/libraries/Faker' // this library is great to generate mock data
export let SignUpDuration = new Trend('Sign up Duration')

let duration = 1000
export let options = {
vus: 10,
duration: '30s',
thresholds: {
'Sign up Duration': [`p(95)<${duration}`]
}
}
export default function () {
let res = http.post(__ENV.HOST + config.api.signUp, {
"email": 'QA_TECH_' + faker.internet.email(),
"password": faker.internet.password(),
"language": "vn", "gender": "M"
})
check(res, {
'status is OK': res => res.status == 200,
'transaction time is less than threshold': res => res.timings.duration < duration
})
SignUpDuration.add(res.timings.duration)
sleep(1)
}

Then run with below command.

k6 run -e HOST=https://www.example.com --vus 5 --duration 10s tests/signUp.js

And K6 outputs nice result to the console.

/\      |‾‾|  /‾‾/  /‾/   
     /\  /  \     |  |_/  /  / /    
    /  \/    \    |      |  /  ‾‾\  
   /          \   |  |‾\  \ | (_) | 
  / __________ \  |__|  \__\ \___/ .io
execution: local
     output: -
     script: tests/signUp.js
duration: 10s, iterations: -
         vus: 1,   max: 1
done [==========================================================] 10s / 10s
✗ transaction time is less than threshold
     ↳  0% — ✓ 0 / ✗ 2
    ✓ status is OK
✗ Sign up Duration...........: avg=2816.323819 min=1926.378042 med=2816.323819 max=3706.269597 p(90)=3528.280442 p(95)=3617.275019
    checks.....................: 50.00% ✓ 2   ✗ 2  
    data_received..............: 5.0 kB 504 B/s
    data_sent..................: 921 B  92 B/s
    http_req_blocked...........: avg=101.78ms    min=1.87µs      med=101.78ms    max=203.57ms    p(90)=183.21ms    p(95)=193.39ms   
    http_req_connecting........: avg=34.57ms     min=0s          med=34.57ms     max=69.14ms     p(90)=62.22ms     p(95)=65.68ms    
    http_req_duration..........: avg=2.81s       min=1.92s       med=2.81s       max=3.7s        p(90)=3.52s       p(95)=3.61s      
    http_req_receiving.........: avg=218.81µs    min=195.49µs    med=218.81µs    max=242.14µs    p(90)=237.47µs    p(95)=239.8µs    
    http_req_sending...........: avg=1.64ms      min=354.72µs    med=1.64ms      max=2.93ms      p(90)=2.67ms      p(95)=2.8ms      
    http_req_tls_handshaking...: avg=66.86ms     min=0s          med=66.86ms     max=133.73ms    p(90)=120.36ms    p(95)=127.04ms   
    http_req_waiting...........: avg=2.81s       min=1.92s       med=2.81s       max=3.7s        p(90)=3.52s       p(95)=3.61s      
    http_reqs..................: 2      0.199997/s
    iteration_duration.........: avg=3.92s       min=3.13s       med=3.92s       max=4.7s        p(90)=4.55s       p(95)=4.63s      
    iterations.................: 2      0.199997/s
    vus........................: 1      min=1 max=1
    vus_max....................: 1      min=1 max=1
ERRO[0012] some thresholds have failed

Key metrics (https://docs.k6.io/docs/result-metrics)

- **http_reqs**: total requests generated & total request per second (more is better)

- **http_req_duration**: total time for server to process a request and respond completely (less is better)

(equal to http_req_sending + http_req_waiting + http_req_receiving)

- **vus**: number of virtual concurrent users generated

- **iterations**: number of times the VUs executing the script

- **checks**: number of failed checks

Write load test with K6 is really quick and friendly to work. Their API provide useful checks and threshold to test and establish baseline for load test results.

Locust with Python is also nice to work with but now I may find a great alternative to it.