ADR 0059's recovery path: the pieces that run when the host will not start.
internal/upgrade -- two facts, neither of them the host judging its health.
Whether the executable this process started from has been replaced on disk, and
which version last completed a reconcile.
The first design was wrong and the tests caught it, not review. It asked
/proc/self/exe whether it was marked deleted. That is Linux procfs behaviour
rather than a fact about files, and it catches only unlink -- a binary swapped
by rename onto the same path reads as untouched, which is exactly what a
package manager does. Now the identity is captured at start and compared later:
no procfs, and neither case missed.
known-good is one bare line. The reader is a shell script on a machine where
the host is failing to start, so it must not need a parser to be present and
working. Written only after a clean apply, which is the whole claim -- not
health, because a disconnected node is ordinary and a failing resource is the
machine's problem rather than the binary's.
packaging/ -- the unit, the rollback unit, and the rollback script. The script
shares no code with the host and calls none of it: a binary that cannot start
cannot be its own recovery. POSIX sh, nothing that has to be installed. The
unit carries Restart=always with a comment saying why on-failure would break
every upgrade.
Both are tested and both sets of tests were confirmed to bite. Injecting five
faults broke exactly the intended tests -- except one, and chasing why it did
not found a placebo assertion I had written: `check "exits zero" ... "0" "0"`
compares a literal to itself and can never fail. Replaced with the real exit
code, after which the injection bites.
Also caught: an injection that produced a build failure rather than a test
failure, which my grep read as "no failure". Re-run so it compiled, and the
test did bite.
The script test runs in `make check`, so it is a gate rather than something
that was run once.
Verified against the real binary: known-good is written beside the store after
a clean apply and is NOT written after a failed one.
jschoubben
f4143806c2