Uhhh... backups?! Not all companies release daily, weekly, and sometimes not even monthly. Stage the rollout, do your testing, get your evidence, get your plan, perform the release.

I think it’s flawed to think that you can safely have multiple versions of the same app running (or even installed) simultaneously in the same “universe.” Whether you use jails, VMs, containers, or whatever you should not count on “I didn’t change anything between these two versions that would corrupt the other instance” to help you.

In a real sense, yes. Once it's deployed, it incurs costs, like a debt.

Reminds me of:

> My point today is that, if we wish to count lines of code, we should not regard them as “lines produced” but as “lines spent”: the current conventional wisdom is so foolish as to book that count on the wrong side of the ledger.

-- Edsger W. Dijkstra