felhom.eu/documentation/architecture/09-update-architecture.md

09 — How an app update works, and what it is becoming

LIVING DOCUMENT. Every slice of the update arc updates this file in the same session. Opened 2026-09-02 with slices 1 and 2. Its absence was R-438: the update mechanism was chosen deliberately and written down nowhere, which is how a deliberate design gets "fixed" by someone who did not know it was one.

This file carries the REASONING. The register (backlog/OPEN-ITEMS.md) carries the work. The source is the truth. Nothing here is invented: every mechanism claim is cited either to audits/SPIKE-app-update-2026-09-01.md, which measured it live, or to live source at file:symbol.

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1. How an update works today, as measured

1.1 The button

Manager.UpdateStack (felhom-controller/controller/internal/stacks/manager.go:1199) is two compose commands and nothing else:

compose pull                       →  compose up -d --remove-orphans

No safety copy. No rollback. No hold. No verification. Confirmed by reading and across six live updates (spike §10 item 6). A pull FAILURE is handled correctly — UpdateStack returns after the failed pull and never reaches up -d, so the running app survives untouched (measured twice, spike §4 3a). A pull that succeeds over an image that then fails to RUN is the bad case, and it is R-443.

1.2 The catalog syncer moves the file underneath a deployed app

Syncer.copyTemplates (felhom-controller/controller/internal/sync/sync.go:319) copies docker-compose.yml and .felhom.yml into every stack folder on a 15-minute cycle (internal/config/config.go:351, default 15m). It has no deployed check of any kind. Its only guard is a sha256 content compare in copyIfChanged (sync.go:403) and its only exclusion is app.yaml. The post-sync hook is stackMgr.InjectMissingFields(updated) and nothing else — the sync does not restart anything.

That is why a deployed app's compose file and its running containers can disagree indefinitely. Measured live 2026-09-01: a real catalog pin change travelled the real cycle, the sync rewrote the deployed app's file at 17:45:17Z, and the container went on running the old image (spike §3).

1.3 Thirteen other paths end in compose up -d

Excluding the three API actions, 13 call sites across 9 files call StartStack or RestartStack, and every one ends in compose up -d against the live compose file (spike §8 — the task that commissioned the spike said five; the count is thirteen). They include the boot reconciler (bootrecon.go:269), the app-stop guard's recovery (appstop_marker.go:283), the drive-return gate (intermediary.go:222), the quiesce restart-after-backup, off-site reconstitution, and every restore path.

So an upgrade can happen with nobody pressing anything — measured, spike §2 variant 1c-ii, where a boot reconciliation started an app on a newer image at 17:55:44Z.

1.4 One fear is measured SMALLER than it was stated

A plain power cut does not upgrade anything. Docker's own restart: unless-stopped puts the existing containers back on the OLD image, so the boot reconciler finds no orphan and never runs up -d — it says so in its own words: no boot-orphaned apps (nothing to start) (spike §2, variant 1c, a positive observable and not an absent log line).

The unattended upgrade needs the narrower precondition: "and the app did not come back." Saying so is more useful than leaving the scarier version standing.

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2. What was chosen, and by whom

Manager.RestartStack (internal/stacks/manager.go:1161) carries this comment, and it predates the whole arc:

"Use up -d instead of bare restart so that env vars from app.yaml are injected and any template changes (new images, healthchecks) are picked up. Plain docker compose restart only sends SIGTERM+start to existing containers without re-reading the compose file or env."

So the restart behaviour was chosen, deliberately, and written down. A design decision is not a defect. What was never decided — and is recorded nowhere — is what happens once the catalog syncer moves the file underneath a deployed app, and whether the choice was meant to extend to the thirteen unattended call sites. That gap is R-438, and it stays open: this document records the mechanism; it does not change it.

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3. The operator decisions

These are rulings, not proposals. Anything specced against a different assumption is wrong.

2026-09-02

1. The safety copy is a verified recent backup as a PRECONDITION — not a new copy invented for the update path. The guest-snapshot alternative is to be spiked before anything is designed around it. Context: the existing safety machinery (Manager.writeSafetyDump, internal/backup/offbox_reconstitute.go:207) is database-only, which is the headline of spike §6 — the file half was never priced, and demo-hp is too young a box to price it.

2. The support window runs on HOW FAR BEHIND THE CATALOG a box is, not on how old its version is. A customer on the newest version is supported however old that version is. This is why catalog_since exists and why no version string is shown.

3. Updates are automatic WITHIN a major, never ACROSS one. The cross-major case needs a human, because §4 says it cannot be undone.

2026-09-06 — Option 1: freeze the version, keep the fixes flowing. SHIPPED, v0.235.0

4. An app's version is frozen to what the customer has, and only a deliberate Update moves it — while corrections to its definition keep arriving on the 15-minute cycle exactly as they do today.

   This is the ruling R-447 was blocked on, and it was blocked for a good reason: §2 establishes that RestartStack's use of up -d to pick up template changes was chosen and written down in its own comment. Reversing a chosen behaviour is a decision, not a bug fix.

   What the ruling looked at, and why it is not simply "stop the syncer touching deployed apps". The old behaviour had two halves and only one of them was unwanted:

   half	verdict
   a restart/repair silently changes the app's VERSION	unwanted — nobody chose it, nobody is told, and §4 says it cannot be undone
   template CORRECTIONS reach a deployed app, and a broken definition heals itself within 15 minutes	worth keeping — both measured in the spike §3

   So the ruling keeps the second and removes the first. In the operator's own words: while the catalog is offering the same version you are running, its fixes flow to you; the moment it moves to a newer version, you are frozen at what you have until you choose to update.

   It does NOT make the Update button safer. That is slice 4 (R-448), and it is where the backup precondition goes. Slice 3 only stops the other twelve paths from doing the update's job.

2026-09-13 — the database engine finishes its own conversion, and the upgrade test goes wide

5. DBs should be updated when the app moves, with proper precautions, tests and backoff plans — the operator's own words, ruling on SPIKE-r459-mariadb-upgrade-2026-09-06.md. SHIPPED in the catalog the same day: every mariadb: sidecar (bookstack-db, kimai-db, nextcloud-db, romm-db) carries MARIADB_AUTO_UPGRADE=1; MARIADB_DISABLE_UPGRADE_BACKUP stays unset. Not an image change, so catalog_since does not move. The three precautions, because they are the real content of the ruling:

   1. Proven before it ships — upgrade-test.py re-ran E3 and E3b on the changed template and the engine-state field shows the conversion RAN (mariadb_upgrade_info reads the new version, the engine's own check says nothing further is needed, the entrypoint no longer prints skipped due to $MARIADB_AUTO_UPGRADE), with the seeded data reading back after. C3 still returns failed. Evidence: audits/r459-close-2026-09-13/.
   2. Watched as it lands — the change travelled the real 15-minute cycle to demo-hp: the live compose gained the setting, the sync recreated nothing, and one deliberate restart logged MariaDB upgrade not required with the app serving (same evidence directory).
   3. A rule until Slice 4 is built — the Update button still takes no backup, so no template may move a database-engine image across a major version until R-448 ships. Catalog CLAUDE.md states it; scripts/check-engine-major.py enforces it in the pre-push hook (the CI half cannot, R-452); its removal is tracked as R-469 so it is a deliberate act. The setting is inert until an engine major moves, and precaution 3 keeps it that way.

6. The upgrade test goes as wide as possible, through the nightly unattended sessions — the ruling on STATUS.md item 11. Not "the ~25 database apps first": all of them, as the nightly rotation reaches them, one fixture per app through the app's own interface. Browser-only apps become reachable when CC runs on the operator's Windows workstation with Chrome — the claude-in-chrome route that DooPlex does not have — so an app recorded inconclusive for want of a headless seed route (bookstack's file half, R-460) is deferred to that venue, not faked.

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4. The vocabulary ruling — "rollback" is struck

App data CANNOT be rolled back. Measured on Nextcloud (spike §7): once a migration has actually run, putting the old image tag back produces a container that refuses to start —

"the version of the data (32.0.9.2) is higher than the docker image version (31.0.14.1) and downgrading is not supported"

with a positive control proving the data is intact, only unreachable by the old version (§7 6d).

So "rollback" must not appear in any spec for this arc. The two shapes actually available are:

shape	when it applies	what it does
ABORT	before anything migrated	stop, put the old image back, the app runs again
RESTORE FROM A COPY	after a migration ran	the data restore is the whole remedy

There is no third.

4.1 MEASURED 2026-09-06 — and the abort turns out to be a property of the APP, not of upgrades

SPIKE-upgrade-test-2026-09-06.md upgraded three real apps with real data in them and then attempted the abort on each. All five real catalog upgrades kept the customer's data. The abort did not behave the same way twice:

app	abort	why
docmost 0.25.3→0.95.0	REFUSES	the old code finds migration ledger entries it does not know: "corrupted migrations: previously executed migration 20260213T085259-notifications is missing", then "Failed to run database migration. Exiting program."
privatebin 1.7.5→2.0.5	works	file-backed, no database, no schema — a major version moves no data
bookstack app+engine	works, misleadingly	only because the MariaDB datadir upgrade was skipped and never happened — see R-459

This puts TWO independent measurements behind the ruling above, by two unrelated mechanisms: Nextcloud refused on an explicit version comparison; docmost refuses on its migration ledger. The word "rollback" was already struck; it is now struck on evidence rather than on one case.

And it adds a distinction this document did not have: there is no single answer to "can this update be undone". There are apps where it can and apps where it cannot, and the only way to know which is to MEASURE THAT APP. Any design that assumes one answer for all 53 is designing against a fact that was checked and is false.

Per §5 below, a restore's image-level undo used to have a ≤15-minute half-life because the syncer overwrote it (R-441) — closed in v0.235.0.

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5. The shape, as SHIPPED in v0.235.0

The live docker-compose.yml is DERIVED from a pin recorded in app.yaml — the one file the syncer never touches. The catalog proposes; app.yaml decides; the compose file is an output rather than an input, and the thirteen unattended up -d paths stop being able to change a version by accident.

5.1 Nothing was added to the thirteen call sites, and that is deliberate

They are made safe by removing the reason, not by gating them. The most important of them are REPAIRS — the boot reconciler (bootrecon.go:269), the drive-return gate (intermediary.go:222), the app-stop guard (appstop_marker.go:283). A repair path that refuses to repair leaves a customer's app down, which is worse than the problem this slice solves. Since the file they act on no longer changes version, every one of them became safe without being touched.

5.2 The pin, and what it is not

AppConfig.PinnedImages (app.yaml, pinned_images:), service → image ref.

It is NOT InstalledImages. That field is an OBSERVATION — what containers report. This one is a DECISION — what should run. Letting an observation feed a decision would make a bad reading become a bad deployment, which is the category error desired_state exists to avoid (R-166), one field over. They will normally agree; when they disagree that is a signal, not a bug to paper over.

Absent means UNPINNED, and unpinned means the app behaves exactly as it did before v0.235.0.

Beside it, applied-compose.yml in the stack directory stores the exact definition that pin came from. Syncer.copyTemplates copies exactly docker-compose.yml and .felhom.yml, so that name is safe from the catalog, and keeping it beside the app means it travels with every path that already moves a stack dir.

5.3 The four writers — the only acts entitled to move a version

writer	pin source
the deploy path (runComposeDeploy)	the template just deployed from
UpdateStack	the catalog's current template, written BEFORE the pull
the restore (stackAdapter.RecreateStackDefinitionFromUnit)	the recovery unit's captured compose — this closes R-441
Manager.AdoptPins	the observation, once, and only when complete AND matching

UpdateStack's ordering is load-bearing, not stylistic. compose pull and up -d act on the file on disk, so the catalog's definition has to BE that file before either runs. A pin set afterwards would pull the frozen version and change nothing — while reporting success, and a button that lies is worse than a button that refuses. A failed pin write REFUSES the update, which is the opposite of recordInstalledImages and for the same reason desired_state refuses: this field is intent.

5.4 The render table, complete

app state	result
not deployed / protected / seam not wired	the catalog template — today's behaviour
deployed, unpinned	the catalog template + one DEBUG
deployed, pinned, catalog images equal	the catalog template — fixes flow, self-healing works
deployed, pinned, catalog images differ	the stored applied definition — frozen WHOLE
pinned, differ, nothing stored	the catalog template + one WARN. We cannot freeze what we do not have and must not invent it
mid-deploy	the compose file is left alone this cycle

.felhom.yml is copied verbatim in every case — it carries no image, and it carries catalog_since, which the badge needs. See §8.5.

The frozen branch writes a WHOLE file and never a substitution. Taking the new template and putting the old refs back creates a third state nobody chose: wger 2.6 needs a full DB configuration the older template cannot supply, so an old image under a new template is broken in a way neither version is.

And this is not "skip deployed apps". That option was considered and rejected: it also stops health-check fixes, memory limits and new deploy fields, and it destroys the self-healing measured in the spike §3 — both halves the ruling explicitly kept.

5.5 Adoption, and why the startup order matters

AdoptPins runs once at boot, immediately after BackfillInstalledImages, and pins every deployed app to what it is already running. It reads and writes files only — no container is started, stopped or touched. It skips, loudly, when the observation is incomplete or when the app runs something the current template no longer offers; those apps keep pre-v0.235.0 behaviour rather than receive a guessed pin.

syncer.Start() was moved to after adoption. It fires an immediate sync; at its previous position that first sync ran while every app was still unpinned, copied the catalog over a deployed app, and handed the next restart a version change — the exact behaviour this slice removes, once per boot.

5.6 The trap this slice set for the previous one

Stack.TemplateImages is read from the app's live compose file — which is now the RENDERED one. On a frozen app that file names the OLD version, so web.compareInstalledToTemplate would find installed == template and answer „Naprakész" on exactly the apps that are behind — with every test still green, because the new field has the same type and shape. The badge now reads Stack.CatalogImages, taken from the syncer's own git clone. A feature that silently inverts an earlier feature is the failure mode to look for whenever a file changes meaning.

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6. The seven slices

#	slice	status
1	The box records what it actually installed — app.yaml.installed_images, per compose service, ref + digest + first-seen.	SHIPPED, controller v0.233.0 (2026-09-02)
1b	Seed the record for apps nobody touches — a startup backfill, so the label is not restricted to apps that happen to get restarted.	SHIPPED, controller v0.234.0 (2026-09-03)
2	One badge says whether the app is current — „Naprakész" / „Frissítés elérhető — N napja", from catalog_since. No version number.	SHIPPED, controller v0.233.0 + catalog 69761cf (2026-09-02)
3	The compose file becomes DERIVED — the pin in app.yaml wins; the syncer renders instead of copying.	SHIPPED, controller v0.235.0 (2026-09-06) — operator ruling §3.4
4	A guarded update — verified-backup precondition, abort-on-failure, and the truth at the moment of action rather than 5m16s later (R-443).	OPEN — R-448
5	An upgrade test that runs again — a harness that upgrades a real app with real data in it and asks the app for the data back.	SHIPPED, app-catalog/scripts/upgrade-test.py (2026-09-06) — 7 edges, 3 apps; see §4.1 and §10
6	A version sequence — updates automatic within a major, a human across one; an engine change gets its own edge.	OPEN — R-450
7	A fleet sweep pipeline — the operator can see, and move, how far behind every box is.	OPEN — R-451

The verdict record — the contract Slice 6 carries

Decided here rather than invented twice. The harness writes one of these per edge, beside its evidence; Slice 6 puts the same shape in the catalog.

{"harness_version": 1, "app": "bookstack",
 "from": {"bookstack": "…:25.02.2", "bookstack-db": "mariadb:11.6"},
 "to":   {"bookstack": "…:26.05.2", "bookstack-db": "mariadb:12.3"},
 "verdict": "proven | failed | inconclusive",
 "seed_read_before": true, "seed_read_after": true, "healthy_after": true,
 "migration_observed": "verbatim log line, or null",
 "abort": "starts-and-serves | refuses | starts-data-gone | not-attempted",
 "abort_detail": "the refusal quoted verbatim, or null",
 "duration_s": 0, "measured_at": "RFC3339", "evidence": "relative path"}

inconclusive is a first-class verdict and must never be collapsed into failed. "We could not measure it" and "it does not work" are different facts, and only one of them is about the app. migration_observed is a quoted line, never an inference from timing — the value of both the Nextcloud and the docmost findings was the exact sentence the app printed.

Database engines under an upgrade — MEASURED 2026-09-06

The arc's standing rule that an engine change gets its OWN edge now has measured evidence behind it, and the evidence is stronger than the rule's original argument. The rule was justified by "two migrations behind one edge is an unreadable failure when it breaks" — a readability argument. What was measured is that an engine change can be applied and silently NOT happen, which the app-half edge cannot produce and which no amount of readability would have surfaced:

• SPIKE-upgrade-test-2026-09-06.md §4 — MariaDB 12.3 starts on an 11.6 datadir, logs that the conversion it requires was skipped, and serves. Assigned to the engine half by decomposition: the app half alone produces no such line.
• SPIKE-r459-mariadb-upgrade-2026-09-06.md — it is stable but never self-resolving (5 of 5 restarts, no degradation, and the engine says Check required! every time, forever). Converting properly succeeds, costs 7 s, takes its own system-database backup, and does not cost the ability to abort. The trade that was expected here does not exist.
• 2026-09-13 — the setting is in the catalog. All four mariadb: sidecars carry MARIADB_AUTO_UPGRADE=1 (operator ruling, §3 decision 5), and upgrade-test.py's engine-state field now shows the conversion RUNNING on the bookstack edges. And a gate holds the engines inside their major until Slice 4: app-catalog-felhom.eu/scripts/check-engine-major.py (R-469).

Two rules for anything this arc builds around a database engine:

1. Ask the engine, not the log. MariaDB's entrypoint prints MariaDB upgrade not required on an unsupported downgrade; mariadb-upgrade --check-if-upgrade-is-needed names it exactly (R-464). A cheap instrument built on the log line would report "fine" for the broken case.
2. The two engines fail in opposite directions, so one check will not do. MariaDB starts anyway and skips quietly; PostgreSQL refuses to start on a datadir from an older major, and the image performs no pg_upgrade. Eleven templates carry PostgreSQL and eight sit on postgres:16-alpine (R-463).

And an engine-state field belongs BESIDE a verdict, never inside it. upgrade-test.py reports engine_state_after next to verdict, because an unconverted datadir is not known to be a failure and a verdict that said so would encode an unproven judgement.

The rule slice 6 inherits, recorded now while it is cheap: an engine change gets its own edge, never bundled with an app version bump. bookstack moved the application and MariaDB 11.6 → 12.3 in one commit (0b73e5e); that is two migrations behind one edge, and an unreadable failure when it breaks.

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7. What slices 1 and 2 actually built

7.1 The record (slice 1)

Manager.recordInstalledImages (felhom-controller/controller/internal/stacks/installed.go) runs after a successful compose up from StartStack, RestartStack, UpdateStack and runComposeDeploy, and writes app.yaml:

installed_images:
  web:
    ref: lscr.io/linuxserver/bookstack:26.05.2
    digest: sha256:…              # "" if the image was never pulled from a registry
    at: "2026-09-02T18:41:03Z"    # when this ref+digest was FIRST seen for this service

Three rules, each with its reason:

• It reads the CONTAINER, never docker-compose.yml. §1.2 is why: that file is the value that has already moved. A record built from it would answer "what will happen next time something runs up -d", which is a different question.
• A failed write NEVER refuses the action — deliberately the opposite of SetDesiredState. Intent refused, observation logged. Refusing to start a customer's app because we could not write down which version it is trades a real outage for a bookkeeping gap.
• It is NOT called from StartStackServices — the R-47 DB-only restore window would overwrite a complete record with a partial one.

Seeded at startup (v0.234.0). Manager.BackfillInstalledImages runs once at boot, beside the desired-state backfill and before the boot reconciler, and records what every deployed app is ALREADY on. It only READS containers. This was not a refinement — without it the feature did not reach a quiet box at all: see §8.3, which was written as a known limitation on 2026-09-02 and was a defect by the next morning.

Two admission rules, and the second is the design:

• It never overwrites an existing record. The bring-up paths own updates; this fills gaps only.
• It refuses to seed a PARTIAL observation. §7.2's comparison reads a service-count mismatch as BEHIND, so a degraded or crash-looping app seeded from its visible containers would render „Frissítés elérhető" over an app that is perfectly current. The bring-up paths may write a partial because they follow a SUCCESSFUL up -d, where a gap is real news and is logged; a backfill meets a box in whatever state it is in. Same field, two writers, two different admission rules — that is deliberate and must not be "made consistent".

Nothing reads it to take a decision. Slice 2 reads it to render a label.

7.2 The label (slice 2)

web.updateBadge (internal/web/updatebadge.go) compares the recorded reference per service against what the current template pins, and renders through the existing meta_badge partial — no new markup, no new CSS.

Absent means UNKNOWN and never means current. Every app.yaml written before v0.233.0 has no record, so a fall-through to „Naprakész" would have told the whole fleet their months-old apps were current. This is the R-166 lesson applied to an observation instead of an intent, and it is pinned by a test with a companion red-proof.

No version number reaches the customer (operator ruling: a household cannot act on 26.05.2). Version strings stay in the logs, the API and the hub.

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8. Known limitations, stated plainly

1. „Naprakész" can be FALSE for the 23 floating pins. The comparison is reference-to-reference and queries no registry — a customer's box must not depend on reaching eight upstream registries to render a page. For postgres:16-alpine, mariadb:11.6 and 21 others the reference can be identical while the image behind it has moved. Measured, not theorised: spike §5 found mariadb:11.4 and mariadb:12.3 had both already moved upstream, with two fully-pinned controls holding. Digest-level comparison needs a registry query and is deferred — R-446.
2. Nothing enforces catalog_since. A commit that moves an image: line and forgets the date under-reports how far behind a box is. The gates runner fetches at --depth 1 and has no parent commit to diff against, so the gate needs a deeper fetch — R-452.
3. The record only appears after the next lifecycle action. CLOSED in v0.234.0, and the way it closed is worth keeping. This was written on 2026-09-02 as an accepted limitation — "the fleet view fills in gradually". The operator looked at demo-felhom the next morning and found OpenGist, up 15 hours, running exactly the catalog pin, showing nothing at all. On a quiet box "gradually" means "never", and a feature that fills itself in on an event nobody triggers is, on the quiet installations, not shipped. BackfillInstalledImages now seeds the absences at startup by reading containers (§7.1). The residue that stays: the seed happens at controller START, so a box between upgrade and its next restart still shows nothing — bounded by one restart rather than unbounded.
4. A frozen app is frozen WHOLE. While the catalog is ahead, no template correction reaches that app — not even one unrelated to the version. That is the direct consequence of §3.4 and of the wger 2.6 hazard, and it is the right trade: a new template around an old image is a third broken state. Recorded so it is a choice, not a surprise.
5. .felhom.yml keeps flowing while the compose file is frozen — the deliberate asymmetry in §5.4. So a frozen app can receive a health check written for a NEWER version and read as degraded. The failure direction is a false alarm, never data loss, and freezing .felhom.yml would break the update badge by withholding catalog_since. R-458.
6. The Update button is still unguarded. It takes no backup, has no rollback, and can still attempt a multi-major jump the app will refuse (R-40). Slice 3 did not change that and must not be read as having done so — the precondition is slice 4 (R-448).
7. An engine major can be applied without its datadir upgrade, and nothing notices. CLOSED 2026-09-13 for MariaDB (R-459): every mariadb: sidecar carries MARIADB_AUTO_UPGRADE=1, and the harness shows the conversion running on the E3/E3b edges (§3 decision 5). What stays true: the PostgreSQL half (R-463) has no equivalent — the image performs no pg_upgrade — and the engine-major rule (§3 precaution 3, R-469) is what keeps both engines inside their major until Slice 4 gives the Update button a backup.
8. Only three of 53 apps have ever had an upgrade measured, and one of them (bookstack) can only be half-proven headlessly (R-460). The widening is R-462, costed with real numbers.
9. The hub does not record image tags at all. Its report's container payload carries name, state, CPU and memory, and no image field (spike §5). So the fleet view of §6 slice 7 needs a hub-side change; it is not derivable from what is already reported.

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9. Where the rest lives

what	where
the measurements this document rests on	audits/SPIKE-app-update-2026-09-01.md
the work	backlog/OPEN-ITEMS.md — R-438..R-445, R-446..R-452
the syncer, described accurately but without the consequence	architecture/02-controller-module-map.md
what the lifecycle actions are proven to do	architecture/00-capability-map.md
the implementation	felhom-controller/controller/README.md §"What is installed, and is it current?"