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Constant VUs

With the constant-vus executor, a fixed number of VUs execute as many iterations as possible for a specified amount of time.

For a shortcut to this executor, use the vus and duration options.


Besides the common configuration options, this executor has the following options:

duration(required)stringTotal scenario duration (excluding gracefulStop).-
vusintegerNumber of VUs to run concurrently.1

When to use

Use this executor if you need a specific number of VUs to run for a certain amount of time.


This examples schedules 10 VUs to run constantly for a duration 30 seconds.

1import http from 'k6/http';
2import { sleep } from 'k6';
4export const options = {
5 discardResponseBodies: true,
6 scenarios: {
7 contacts: {
8 executor: 'constant-vus',
9 vus: 10,
10 duration: '30s',
11 },
12 },
15export default function () {
16 http.get('');
17 // Injecting sleep
18 // Total iteration time is sleep + time to finish request.
19 sleep(0.5);


The following graph depicts the performance of the example script:

Constant VUs

Based upon our test scenario inputs and results:

  • The number of VUs is fixed at 10, and are initialized before the test begins;
  • Overall test duration is fixed at the configured 30 second duration;
  • Each iteration of the default function is expected to be roughly 515ms, or ~2/s;
  • Maximum throughput (highest efficiency) is therefore expected to be ~20 iters/s, 2 iters/s * 10 VUs;
  • We see that the maximum throughput is reached and maintained for the majority of the test;
  • Approximately 600 iterations are therefore performed in total, 30 seconds * 20 iters/s.