A provisioning script maintained since 2019 and never once run against an empty machine.
the first run, against a fresh host:
failed at step 4 a package renamed in 22.04
failed at step 11 a directory the script assumed
existed, created by step 3 in a
version deleted in 2021
failed at step 19 a service enabled before its
configuration was written
succeeded on the fourth attempt, 41 minutes
and the running host had none of these problems,
because it had never been provisioned by this script.A script that only ever runs against an already-working host converges to describing that host rather than producing it. The four attempts are the honest cost of six years of not testing it, and the check that stops it recurring is a monthly CI job that provisions a throwaway machine and destroys it.