Kubernetes Operator / Controller
https://zoetrope.github.io/kubebuilder-training/controller-tools/crd.html
https://speakerdeck.com/nwiizo/kubernetes-operator-implementation-and-melancholy
https://cstoku.dev/posts/2018/kubebuilder-intro/
https://www.kaitoy.xyz/2019/03/08/k8s-zundoko-operator/