immutable-infrastructure
Immutable Infrastructure
Every server that's ever been SSH'd into to fix something is now a unique, undocumented artifact — its actual state exists only on that machine, not in any repo. Multiply that by a fleet and you get servers that have quietly diverged from each other in ways nobody can enumerate, discovered only when one of them fails differently than the rest.
Immutable infrastructure closes that gap by removing the option: nothing is ever changed on a running instance. To make a change, you build a new image and replace the instance that's running the old one. There is no in-place path, so there's no drift to accumulate.
Servers are cattle, not pets — you don't nurse a sick one back to health, you replace it and move on, and the fact that you can tell them apart at all is the bug.