The live Nextcloud 31→34 climb left 4.4 GB of images behind — one per
rung, each ~1.5 GB, all still present after it finished. On a small VPS
that is the difference between working and full.
`system reclaim` cannot help: it collects DANGLING images, and every rung
is a real tag, so all of them stay tagged and stay on disk. (Rolling apps
never hit this — moving a floating tag orphans the old image, which
reclaim then collects. It is specific to laddering.)
After a SUCCESSFUL climb only, remove the images stepped through, keeping
the immediately-previous version so a roll-back needs no download.
CFG_UPDATER_UPGRADE_PRUNE=false keeps everything. Never runs on failure,
where the older images are exactly what recovery may need.
Tested: a 3-rung climb removes 31 and 32 and keeps 33; a single-step
climb removes nothing (its previous version IS the rollback target); the
config switch disables it.
Found by looking at the box after the first real ladder run — the feature
worked, and then quietly cost 4.4 GB.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Ties the ladder and the verifiers together behind a new verb:
libreportal updater upgrade <app> [version] [--dry-run]
Per rung, and every part is load-bearing:
snapshot (fail-closed) -> set version -> pull -> up -> VERIFY -> next
On failure anywhere: restore THIS rung's snapshot, put the version back,
stop, and leave the app on the last version it actually verified at. The
ladder never continues past a doubt.
A snapshot PER RUNG rather than one at the start, because upstream
migrations are usually one-way — Nextcloud 32's schema cannot be undone
by putting the 31 image back. The recovery guarantee is "restore the
snapshot from sixty seconds ago", which only holds if every rung has one.
Two gates before anything moves. An app with no <app>_upgrade_verify is
refused outright: the generic health check cannot see a half-finished
migration, so laddering on it would be a guess wearing a safety label.
And a ladder that cannot be computed end to end refuses rather than
attempting a partial climb.
`updater upgrade` is a separate verb from `apply` on purpose: apply moves
you WITHIN a release line (and may be automatic), upgrade moves you
BETWEEN lines and is always a deliberate act. Dry runs execute inline so
the plan is instant to read.
updaterSetAnchorVersion rewrites the image tag AND its version sentinel
together — updating only the image would leave the sentinel advertising
the old version, and the next config regeneration would silently revert
the app.
Tested with stubs against the real code paths: the no-verifier gate holds
and changes nothing; a dry run has zero side effects; the happy path
snapshots at each current version before moving; a verify failure on rung
2 of 3 stops with the app on rung 1, restored, and never touches rung 3;
a failed snapshot moves no version and pulls nothing; a container that
will not start is rolled back.
NOT yet exercised on a live install — no app here needs a ladder. The
first real run should be a dry run.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
