[throwaway823882]

A Kubernetes cluster already runs on cobbled together shell scripts. The K8s build and setup files, Dockerfiles, in-lined commands in kubectl files. Shell scripts are just small simple programs.

Immutable Infrastructure isn't magical at all, it's a paradigm shift which has real world effects. And you can do it with plain VMs and some software inside. But the VM has to be immutable, and the software inside should be as immutable as possible. Otherwise you are constantly fighting a battle to "fix" the state over and over again, and you can't clearly reason about the operation of the system.

Immutable Infrastructure doesn't solve the halting problem, it avoids the halting problem, because it depends on not having general algorithms and unlimited input. It instead uses specific operations with specific criteria in a predictable way, the way safety systems are designed.