Unable to scale maxVUs down in externally-controlled executor

[imiric]

In v0.26.2 it was possible to scale maxVUs arbitrarily using the REST API or the helper scale -m command.

On the current new-schedulers branch (2f150f2), it's only possible to scale maxVUs up, but not back down, and no errors are returned when attempting to do so.

Environment

• k6 version: new-schedulers (2f150f2)
• OS and version: Linux
• Docker version and image, if applicable:

Expected Behavior

• It should be possible to scale maxVUs down to the initial maxVUs setting.
• Trying to scale maxVUs below the initial maxVUs setting should return an error. This is a slight breaking change from 1007 in order to allow VU sharing between executors.

Actual Behavior

k6 scale -m N where N is below the currently set maxVUs value (whether that was the initial value or one scaled up to with k6 scale -m previously) is silently ignored, and the executor remains with the previous value.

Steps to Reproduce the Problem

1. Given the following script.js:

import { sleep } from 'k6';

export let options = {
  scenarios: {
    adjustable_at_will: {
      executor: "externally-controlled",
      vus: 0,
      maxVUs: 20,
      duration: "10m",
    },
  }
};

export default function () {
  sleep(1);
}

2. Run k6 run script.js.
3. In another terminal, run k6 scale -m 50. Note the vus-max: "50" in the output.
4. Run k6 scale -m 20. Note that vus-max remains at 50.
5. Run k6 scale -m 10. Note that vus-max remains at 50 and no error is returned.

Also, make sure that the behavior of scale -u is also consistent, and returns errors in the same way as v0.26.2.

[imiric]

Closed by #1517.