9b7da9f2d2
Enabling a plugin could not make its routes live. Flask refuses
register_blueprint once the app has served a request, and each gunicorn worker
holds its own app object, so registering in the worker that served the toggle
would leave the others answering 404 for the same URL.
Worse, the window before the restart was a window in which workers disagreed
about reality. Four defects, all of which answered 200 while going wrong:
- Enabling a not-yet-installed plugin ALWAYS 500'd on a running app:
install_plugin ran the migrations, updated the registry, and only then called
register_blueprint and hit Flask's assertion. The toggle half-applied and
reported failure.
- Enabling one plugin could hang the entire site. @jwt_required does SELECT
users, so the request's transaction sits open holding a shared metadata lock;
the plugin's migration runs on its own Alembic connection and needs an
EXCLUSIVE lock on users for a foreign key. Each waits on the other, and MySQL
grants metadata locks in request order, so every later login queued behind the
pending exclusive. Observed twice as a total outage from one plugin toggle.
- Each worker rewrote the WHOLE registry file from a snapshot taken at boot, so
concurrent enables erased each other: seven enables persisted three, with
HTTP 200 for all seven.
- Dependency checks read that same stale snapshot, refusing a plugin whose
dependency another worker had just enabled.
Routes still require the process to restart; what changes is who initiates it.
Each worker fingerprints instance/plugins.json at boot and exits gracefully when
it changes, and the supervisor replaces it. That is the primitive gunicorn's own
--reload uses. Recycles are staggered per worker so the pool rolls rather than
dropping at once, and the exit is scoped to gunicorn: on Windows sys.exit() in a
daemon thread ends the thread rather than the process, so IIS keeps the manual
restart until that path is proven on the Windows VM.
The registry now merges under an exclusive lock and replaces atomically, saves
only the entry being changed, and re-reads before any decision is made from it.
ADR-020 records the decision; ADR-013 is amended where it said the UI must tell
the operator to restart. The restart requirement and the honesty requirement
both stand - only the manual step is removed, and only where it is proven.
(cherry picked from commit 9d6342b3ab)
Architecture Decision Records
An ADR captures one decision: the context, the decision, the consequences and the alternatives. ADRs are immutable once accepted. A superseded ADR stays in this folder, marked at the top, pointing forward.
Read the index, not the folder. Find the one line that matches your question, open that ADR, and skip the rest. Nothing here is a prerequisite for anything else.
Which decision governs your question
| ADR | The question it answers | Holds? |
|---|---|---|
| 001 | What may a plugin depend on? What is the versioned platform surface? | In force |
| 002 | How is that surface versioned, and what does a plugin's core_version mean? |
In force |
| 003 | How does a plugin reach a site - bundled, or from its own repo? | In force. ADR-013 added the catalog, artifact and signing on top |
| 004 | One instance per site, or one multi-tenant instance for all sites? | In force, except its "Migration strategy" section, replaced by ADR-008 |
| 005 | Are metrology instruments a separate asset class from machinery? | Superseded by 018. Answer reversed |
| 006 | How does a plugin accept data pushed in from outside? | In force |
| 007 | What version is the PRODUCT, as distinct from the plugin contract? | In force |
| 008 | Whose Alembic chain owns a plugin's tables? | In force |
| 009 | What happens when someone opens a URL belonging to a disabled plugin? | In force |
| 010 | How does a plugin add UI without editing core Vue files? | In force |
| 011 | Why is the code called machines and what happened to machinetypes? |
In force |
| 012 | Does ShopDB own GE-Enforce manifests, and does it own the engine? | Record only on this line. The plugin it decided is not bundled here; ADR-013 and the API-token resource scopes trace back to it |
| 013 | How does a site ship only the plugins it chose, and how is plugin code trusted? | In force |
| 014 | Does a lean site still create tables for plugins it never installed? | In force |
| 015 | Where may one site's hostnames, shares and defaults live? | In force |
| 016 | How does a bay get a controller credential without a cleartext file on a share? | Superseded by 019, and never built. Do not build against it |
| 017 | How does the floor map hold more than one floor and more than one building? | In force |
| 018 | Where do CMMs and vision systems live now that measuringtools is retired? |
In force, and this line is the one it describes: there is no measuring-tool asset class |
| 019 | How does the server know WHICH PC is calling, and what replaced the fleet-wide key? | In force |
| 020 | How does enabling a plugin take effect without the operator restarting the app? | A worker fingerprints plugins.json at boot and exits when it changes; the supervisor replaces it. Amends 013 |
Related decisions that are not ADRs, kept as records of why something was built: docs/proposals.
Status vocabulary
The Status: line at the top of each ADR uses these, and nothing else:
- PROPOSED - drafted, awaiting decision.
- ACCEPTED - in effect.
- SUPERSEDED by ADR-NNN - replaced. The link forward is part of the status, and the superseded ADR carries a note at the top saying not to build against it and what changed.
- DEPRECATED - no longer in effect, with no replacement.
Authoring
- Copy the most recent ADR as a template and increment the number.
- Start the file with a
docmetacomment, before the H1. ADRs arepurpose: explanation. - Add a row to the table above: the QUESTION it answers, not its title.
- Add it to docs/INDEX.md too - under "Decisions" while it is
current, under "Archive" once it is superseded. It has to be a table ROW
with its real line count, not a mention in a paragraph:
tests/test_docs_index.pyfails on an ADR no row routes to, and on a row whose line count is stale. - Never edit an accepted ADR's decision. Supersede it with a new one, and mark the old one at the top - ADR-005 and ADR-016 are the worked examples.