Maybe using cert-manager & ingress-nginx to front the service with SSL. Then your ingress-nginx will front your ruby app and decorate it with ssl. Please note, and I am embarrassed it took me so long to figure out - there are two nginx ingress projects - "nginx-ingress" and "ingress-nginx"! I would strongly recommend using the k8s official one, which is ingress-nginx. See:
https://www.digitalocean.com/community/tutorials/how-to-set-...This will help you learn the ingress pattern. After that, I would suggest exploring ways to tack a sidecar on (log aggregator, etc) - my impression is you are just looking for things to learn, I wouldn't normally suggest doing this just to do it.
Alternatively, you could try exploring putting grafana/prometheus in, though this can be a big bite for someone learning, so I would recommend learning/comprehending sidecars/ingress, etc as they are some of the building blocks for k8s.
Edit: I see there's another comment for traefik for ingress - that's fine too, it's the concept that matters, not your particular choice. If you have a lot of trouble implementing one, try the other one, things you learn in your journey will help quite a bit.
