My Raspberry Pi Cluster was running Docker Swarm for the last 3 years and been very happy with it.
Although Kubernetes is very trending, Kubernetes is not always the answer.
For my use-case, running simple 1 container per service applications on Docker Swarm was more than enough, it was lightweight, very suitable for running them on Raspberry Pi's and very easy to get things running.
But I wanted to move my Raspberry Pi Cluster to Kubernetes to learn Kubernetes more, break things, how to fix them etc.
I will be using Rancher's k3s distribution of Kubernetes to deploy to my Raspberry Pi cluster.
See the following posts: