Load testing APIs with Grafana k6

 Trying out Grafana k6 for performance testing. Heard that it is way better than Apache JMeter.

 

Setup

Using k6 with docker is easy. Just pull the image and run whatever test script we have prepared, e.g.:

docker run --rm -i grafana/k6 run - <script.js

And it should output the result similar to this when done:

But I wanted to store the the output and visualize the result, like the screenshot at the top of this post. Especially I wanted to see the impact when increasing number of concurrent access. Hence I have decided to run k6 with timescaledb and Grafana.

Luckily, there is also a docker solution for that. The only changes I have done was modifying docker-compose.yml to mount the database data directory with host folder for easy clean up:

Otherwise, just build the special k6 image that supports timescaledb and start the containers:

docker-compose build k6

docker-compose up -d

Note that the actual k6 container to run the script won't be started by docker-compose. Instead it will be executed separately, e.g. with a shell script:

#!/bin/sh
set -e

TAG_BASE="newssum"
TAG_NAME="$TAG_BASE-$(date +%s)"

docker run --rm --net=host -e K6_OUT=timescaledb=postgresql://k6:k6@localhost:5432/k6 -i xk6-output-timescaledb-k6 run --tag testid=$TAG_NAME - < k6/newssum.js

Test script

I have decided to try out load testing my newssum APIs. The script itself is fairly straightforward. A few points to note:

• the test will be ramping up the number of virtual users (VUs) slowly from 20 to 160 to show the impact on heavy loading
  

• since the newssum APIs cache the result, the script will call them once during the setup stage to preload them
• by default, k6 uses a separate VU to execute the setup (only once, before the actual test start). Hence each VU will need to find out the available "sources" itself in the "default" function when running the actual load test
  

 

 Once the execution is done, result can be visualized with Grafana container by pointing the browser to http://localhost:3000. e.g.:

 

For this specific example, can see that newssum starts to struggle once we have over ~100 concurrent requests as the 95th percentile shoots up.

tl;dr

I can see why developers like k6 over JMeter. It is simple and straightforward to use Javascript to create load tests that require special setup.