DevOps/Cloud
Immutable Infrastructure
Also written as Cattle Not Pets, Server Replacement
Never changing a running server. To deploy or patch, you build a fresh one and delete the old, so no machine accumulates undocumented tweaks.
Think of it like
Replacing a part rather than repairing it in place, so no machine has a history only one mechanic remembers.
Junior or senior?
Underpins containers and infrastructure as code.
Senior sounds like
Has migrated away from hand-tended servers and can describe what broke on the way.
Ask them
“Have you worked somewhere with a server nobody dared rebuild? What made it that way?”