Ultimately the question is, "how much of the total cpu/memory is used just running kubernetes?" I know prior to rpi4, clusters like this were basically demo/education/bragging rights projects.

It's great for edge computing. Chick-fil-a is using something like this at all their restaurants.

https://medium.com/@cfatechblog/bare-metal-k8s-clustering-at...

https://medium.com/@cfatechblog/edge-computing-at-chick-fil-...

If you're serious about messing around with your own k8s cluster, you're way better off just using virtualization. If you really want to run on your own hardware, grab an old laptop or desktop computer and KVM and have at it.

The Pis are just fun toys for people who enjoy tinkering with hardware. This kind of setup isn't really useful (or even educational in any kind of general way outside of the Pi specific details), but some people enjoy it.

It looks like this is being used more as an educational tool for the authors daughter than it is being used for a production workload.

Kube is basically fancy systemd built to run on multiple machines. If you wanted to you could use this for anything you could use one bigger machine and systemd to do.

I started playing with Elixir on mine, but installing Elixir on ARM is enough of a pain that I opted for a Docker image instead so I only had to build it once.