I didn't pay a lot of attention, but doesn't Proxmox support Docker containers? Or is it just Kurbernettes - or whatever...
Proxmox supports containers using LXC, not Docker. It's still containers, but LXC containers are really more intended to be lightweight virtual machines that share a kernel. Although that's technically the same thing, LXC tends to be used for permanently installed, long running virtual machine equivalents, where Docker is used for individual workloads that are sandboxed and often ephemeral in nature.
Kubernetes is a container orchestration engine. It normally uses Docker as its container layer.
I understand the basic concept of these ideas, but it wasn't something on my radar. Is it something that I can easily test under Proxmox? That is supposed to be the advantage of containers, right? They're very simple to throw up?
Yes, and it appears that the easiest way to do that is just to run an ordinary Ubuntu VM on your ProxMox cluster and then run Docker Engine on that. Basically just bring up a clean OS build and then follow the instructions at https://www.citadel.org/docker.html to deploy Citadel. It ought to be ridiculously easy.
Kubernetes (aka K8S) on the other hand, is not easy to install. But unless you're building a cluster there is no need to go that route. I'm trying to wrap my head around K8S because I need it for work. And then you have to figure out your clustering strategy, your storage layer, your network layer, all of which are pluggable... oy.
