jschoubben
f4143806c2
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.
9 lines
280 B
Desktop File
9 lines
280 B
Desktop File
[Unit]
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Description=Roll the Novox Mesh node host back to the last version that started
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# No OnFailure of its own. If the rollback fails there is nothing further to try
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# automatically, and the node needs a person.
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[Service]
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Type=oneshot
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ExecStart=/usr/lib/nox-mesh-host/rollback
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