K6 scale not works with stage

[zefelise]

If I run the script with stage option defined, like:

export let options = {
    stages: [
        { duration: "3m", target: 10 },
        { duration: "10m", target: 35 },
    ]
};

I can not change the vus during the execution with k6 scale cmd.
Every time I change the vus with k6 scale the actual vus will be changed back the one defined in the stage targets soon.
Is this by design or an issue? It's useful that I can trigger a script with pre-defined stages while sometimes try to change the vus in ad-hoc.

[mstoykov]

Hi @zefelise,
I don't think this is well explained on the wiki (at all actually) or in the blog that is linked there, but if you have stages they will continue to work whether or not you use k6 scale actually whatever you have set will work regardless of the k6 scale.
The "correct" way to use this is to no have stages and to have a duration that is bigger than what you will need .. for example 24h. You should probably use --paused as well.

I also should mention that #1007 will change this in a way such that k6 will require you to say that you want to set your vus manually through the API. This (for the moment) will also not let you have stages and other ways to run vus.

[zefelise]

Hi @mstoykov ,
Thanks for the explanation. We have some pre-defined stage settings in the scripts. As your suggestion, maybe I need to run the scripts with --duration with k6 run to override the stage settings so that I can scale the vus later, right?

[mstoykov]

The "correct" way to use the rest API to scale up and down is to run k6 as

k6 run --paused --no-setup --no-teardown --duration 48h --iterations -1 --vus 0 --max 1 --stage "" script.js

After this you should use the API to call the setup function and set the data it returns you through the API, through the API to be the setup data for the tests. And after that you can run scale up and unpause the script. At the end you should scaledown and run teardown, if you have teardown and setup of course :).

All of this is done so that you can actually control what happening instead of k6 to start executing the stages that are defined in the script or running with it defaults(1vu 1 iterations) when you unpause the script. The setup/teardown thing is mostly because of teardown.

As you see the whole experience is not ideal and definitely contra intuitive in a lot of places which is why it is somewhat redesigned in #1007 and will hopefully be at least less confusing ;)

[zefelise]

Thanks @mstoykov . This makes sense.

[mstoykov]

I am going to leave this open and close with #1007