Consider using multi-platform Docker images

[ee7]

Currently, Exercism runs the tests for every user's solution on an AWS x86_64 machine (as far as I know). But the arm64 machines are significantly cheaper for the same (or perhaps even better) performance.

We could consider doing something like this:

1. Modify a few of our used Docker images to be multi-platform
2. Change the backend logic such that multi-platform images prefer to run on an arm64 machine, but use an x86_64 machine if there's no arm64 machine available
3. Replace some of the x86_64 machines with arm64 ones

This could save some money, but may or may not be worth the cost of the developer's time.

It would be more convenient to do this after GitHub provides arm64 runners (which is currently forecast for Q4 2023), so that we can test arm64 Docker images in GitHub CI like we do for the x86_64 images.

---

I mentioned this to Jeremy years ago, but I never created an issue for it. So I'll create an issue now just for tracking/visibility, but feel free to immediately close it as not planned.

Maybe we could have an issue for using spot instances too?

[sedmo]

just wanted to point this out github/roadmap#528 (comment)

[ee7]

Thanks! We've seen that.

Exercism still has no plans to work towards using multi-platform Docker images, as far as I know. And GitHub's new arm64 runners might be expensive enough to significantly eat into the potential savings from using arm64 machines on AWS.

Exercism could set up arm64 runners on other CI/CD providers, but I'd imagine that it's not worth the added complexity. So I don't see multi-platform Docker images happening in the near future.