Ideally your automation and everything else is done so you have a reproducible environment. If that is the case and you recreate the environment when you run into that 15% problem you should be recreating the problem.

Yes there were methods of doing the same thing pre containers. smoother and simpler IMO

Simplest was the ship everything in a tarball using embedded deps so everything was inclusive. Production was pointed to the latest release via a link. New release was done and you simply changed the link. Rollback was as simple as changing the link back to the previous version.