Difference in iterations and http_reqs


Just started using K6 - great tool!

My question, why is there a difference between the iterations and https_reqs? Furthermore, the number of http requests is > the iterations?

http_reqs..................: 2535   211.246168/s
iterations.................: 2077   173.080193/s

I’d expect that to be the same - doesn’t each iteration make a single request?

My script is a basic one:

export default function main() {
  let response = http.get(TEST_URL);
  myFailRate.add(response.status !== 200);



Because, when the specified script duration runs out, or when the configured stages ramp down or finish, current k6 versions abruptly terminate the currently running iterations and don’t emit more metrics from these VUs.

So, in your example, I suppose that ~458 VUs were currently somewhere after the http.get() call in their iteration, but hadn’t finished it, probably busy sleeping. So, when the test ended, they had completed the HTTP request, but not the full iteration, causing you to have more http_reqs metric values than iterations.

We have introduced a new feature in the most recent k6 code, currently available via the Docker master image and slated to be released as k6 v0.27.0 next week. Now k6 has support for gracefulStop and gracefulRampDown, which would be 30s by default. These options will cause k6 to wait (up until the specified time) for any currently running iterations to finish when it has to ramp down or finish the test run, but it won’t start any new ones. In general, unless your iteration takes longer than gracefulStop/gracefulRampDown (and you can always set them to 0 to simulate the old behavior), in the new version iterations should match http_reqs in your example.