1.2.1 Kubernetes
Kubernetes (k8s) runs containers on a pool of nodes. You declare a Deployment; the cluster keeps that many healthy Pods.
Why it matters
At more than a handful of hosts, SSH and systemd do not scale. k8s gives rolling updates, service DNS, and a common API.
How it is used
Package the app as a container. Write a Deployment + Service. Use probes and resource requests. Start simple — managed GKE/EKS/AKS — before running your own control plane.