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## What & why S-19b-1. A write to the Objecten API now produces a **delivered** notification on the `objecten` kanaal in Open Notificaties. ADR-0028 switched Objecten's notifications off on purpose — there was no broker, worker, kanaal or abonnement, so wiring only the client side would have dropped every message on the floor. This slice builds the real path and turns it back on. - `objecten-celery` worker (mirrors `oz-celery`) + `CELERY_BROKER_URL`/`RESULT_BACKEND` on objecten-redis db 1 (db 0 is already the cache). `notifications_api_common` only *queues* the send; without a worker every register write is silently undelivered. - `nrc` service + `notifications_config` in Objecten's `setup_configuration`, reusing the `big-reference-seed` credential OpenZaak publishes with (NRC authorizes it via OpenZaak's AC, which grants it `heeft_alle_autorisaties` — no second credential needed). - The `objecten` kanaal in NRC's `setup_configuration`. The name is fixed by the Objects API (`NOTIFICATIONS_KANAAL`), not chosen here; publishing to an unregistered kanaal is exactly what the red check reported first. - `NOTIFICATIONS_DISABLED: "false"` in both compose files. - Writers address Objecten as `objecten.local` — see *Notes for reviewers*. - `make verify-objecten-notifications` — registers an abonnement on `objecten` pointing at a throwaway sink, writes a `RegisterRecord` exactly as the ACL does on approval, asserts the delivery. One assertion covering the whole chain: Objecten -> objecten-celery -> NRC -> nrc-beat -> callback. Wired into the CI `verify-stack` job and the summary table. **ADR-0029** records the decisions; ADR-0028's ceiling now points at it. Closes #152 ## Definition of Done - [x] Linked Gitea issue (above). - [x] Failing test committed before the implementation (dc9ca2c, red at the first hop: `NRC POST /api/v1/abonnement -> 400 "Kanaal met deze naam bestaat niet."`). - [x] Implementation makes the test pass (4488962, + two fixes found by CI, below). - [x] Conventional Commits referencing the issue (`refs #152`). - [x] CI green — all six jobs ona5fd47e, including `verify-stack` end to end (e2e included). - [x] `docker compose up` from a fresh clone reaches green health checks within 3 minutes (`verify-stack`'s bring-up step). - [x] Docs updated — ADR-0029 added, ADR-0028's ceiling annotated, BACKLOG.md split. - [x] ADR added in `docs/architecture/`. - [x] Demo note in `docs/demo-script.md` if user-visible — n/a, infrastructure only; nothing consumes the kanaal until S-19b-2 (#153). ## Notes for reviewers **The one genuinely non-obvious bit: writers address Objecten as `objecten.local:8000`, not `objecten:8000`.** NRC types a notification's `hoofdObject`/`resourceUrl` as DRF `URLField`, so Django's `URLValidator` runs on them — and it rejects a **single-label** host. Objecten fills both from the object url DRF built with `request.build_absolute_uri`, i.e. *the Host the caller used*. Writing via the plain service name returns 201 and then fails every publish in the background, forever, with ``` 400 {"hoofdObject":["Voer een geldige URL in."],"resourceUrl":["Voer een geldige URL in."]} ``` So the `objecten` service carries an `objecten.local` network alias and every writer uses it — `Acl__Objecten__BaseUrl`, `ObjectenGatewayIntegrationTests`, this slice's verify driver. An alias rather than a bare dotted `SITE_DOMAIN` so the host still *resolves*: a subscriber following `resourceUrl` reaches the record, which S-19b-2 will do. Readers keep the plain name. Same class of constraint as ADR-0028's Objecttypen base-URL rule. **Ceiling, stated in the ADR:** nothing enforces the alias — a future writer using `objecten:8000` gets a 201 and silently no notification. If a second writer ever appears, rename the compose service rather than adding a lint. **Two CI-only failures on the way here**, both worth knowing: 1. `SITE_DOMAIN` was my first guess at the mechanism and is simply not what builds those URLs — dropped ind76abf2. 2. The check correlated the delivery on the `reference` inside the record it wrote. An NRC notification carries `kanaal`/`resource`/`kenmerken`/`hoofdObject`/`resourceUrl` and **never the record data**, so it correlates on the object URL now (a5fd47e). **Cost:** one more long-running container on the memory-tight runner. It inherits the capped `UWSGI_PROCESSES: "1"` env, which the celery command ignores; if `verify-stack` gets tight again, celery concurrency is the next knob. **Follow-up:** S-19b-2 (#153) sources the projection from these events. Nothing subscribes to the `objecten` kanaal in the product yet — only the verify check does.Reviewed-on: #154
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ADR-0028: Objecten holds the register, OpenZaak holds the process
- Status: Accepted
- Date: 2026-08-14
- Deciders: Respellion engineering
- Slice: S-19a (#149), first of the S-19 (#20) split
Context
Until this slice the register existed only as a derived thing: the read projection rows the Event Subscriber builds from NRC zaak notifications (ADR-0008). There is no system anywhere that holds "who is registered" as a first-class record — drop the projection database and the only way back is to replay ZGW history and re-derive it.
That is the wrong shape for a register. A BIG registration is a fact about a person
that outlives the case that produced it: it is looked up, corrected, superseded, and
retained on its own schedule. The zaak that produced it is a process record — it
opens, moves through statussen, and closes. Storing the fact inside the process record
(as zaak eigenschappen, the v1 placeholder PRD §"Registration" mentions) welds the two
lifecycles together: the register can then never be read, retained, or corrected without
going through the case system that happened to create it.
S-18 stood up Objecten + Objecttypen and registered the public-safe RegisterRecord
objecttype (ADR-0027). The open question this ADR closes: where the authoritative
register record lives, and who writes it.
Decision
The register record lives in the Objecten API as a RegisterRecord object. OpenZaak
keeps only the process. On approval the ACL writes both: the ZGW eindstatus, then the
register record.
Not zaak eigenschappen
Eigenschappen are per-zaaktype, untyped strings, and readable only by walking the zaak. They inherit the zaak's lifecycle and its archiving regime, and they give the public register no queryable surface of its own. Objecten gives a JSON-schema-validated record (ADR-0027 makes that schema the disclosure boundary), a queryable collection, and a lifecycle the zaak cannot drag around with it.
The ACL writes it, not the domain or the Event Subscriber
CLAUDE.md §8.1 keeps upstream Common Ground modules behind the ACL. Objecten is such a
module, so the same rule applies: ObjectenGateway is the only code that talks to it,
and the domain keeps handing the ACL nothing but a zaak URL. The alternative — having the
Event Subscriber write the record when it sees the status notification — would make the
register a second derived artefact of ZGW, which is exactly the coupling this ADR
removes.
Two writes, converging rather than transactional
Approval is now two writes across two modules, so it cannot be atomic. Both are made idempotent instead:
- a ZGW status is an append-only log entry, so re-setting the eindstatus is harmless;
- the register write is an upsert keyed on the zaak id — search Objecten for an
existing object with that
id, then PATCH it or POST a new one.
A caller that retries a half-failed approval therefore converges. This is the same eventual-consistency posture as everywhere else in the system (CLAUDE.md §2.2, §8.6), not an exception carved out for this path.
The objecttype is resolved by name, lazily
The objecttype URL and version number are assigned by Objecttypen at seed time, so they
cannot be pinned in config — the ACL resolves them by the configured name
(Acl__Objecten__ObjecttypeName), taking the highest published version. This is the
same reasoning as ADR-0021 for zaaktypen.
Resolution happens on the first approval, not at startup, so the ACL needs no depends_on
on Objecten and will not crash-loop when it boots ahead of the seed. A failed resolution
is not cached, so it is retried on the next approval.
- ponytail ceiling: the resolution is memoised per gateway instance, and the gateway is a
transient typed
HttpClient— in practice one extra GET per approval against a neighbouring container. - Upgrade path: lift it into a singleton cache (as
CachedZaaktypeCatalogdoes for ZGW) if approvals ever get hot enough for that GET to matter.
The objecttype's UUID is pinned, not server-assigned
Objecten refuses to store an object whose objecttype it has not been configured with
(ObjectType with url=… is not configured), and its configuration identifies an
objecttype by UUID — supplied through a static setup_configuration file applied
when the container starts, before the registerrecord-init one-shot has run.
Rather than thread a seed-time UUID from one container into another's config, the UUID is
pinned: infra/objecttypen-registerrecord/register.py creates the objecttype with a
fixed UUID (the Objecttypen API accepts a client-supplied one), and
infra/objecten/setup_configuration/data.yaml declares that same UUID. Both sides are
declared up front, both stay idempotent, and neither has to wait for the other.
The cost is a constant duplicated across two files that must be kept in step; each carries a comment pointing at the other.
The ACL must reach Objecttypen at the URL Objecten knows it by
Objecttypen builds the url it returns from the request's own Host header, and Objecten
matches an incoming object's type against the api_root it was configured with. So an
ACL that reads Objecttypen at http://localhost:8020 gets back a localhost objecttype
URL that Objecten then rejects as "not one of the available choices" — even though it is
the same objecttype.
Acl__Objecten__ObjecttypenBaseUrl must therefore match Objecten's configured
api_root (http://objecttypen:8000/api/v2/). This is the same class of constraint as
ADR-0006's "point the ACL at OpenZaak's container IP", and it is why the Objecten
integration tests only pass from inside the compose network.
Objecten's notifications are off for this slice
Objecten publishes to a Notificaties API on every write, and notifications_api_common
raises rather than skipping when that configuration is absent — so with no NRC wiring,
every POST /api/v2/objects returns 500 after creating and rolling back the object.
Objecten → NRC is not wired: there is no broker, no Celery worker, no objecten kanaal and
no abonnement for it. Configuring only the client side would make writes succeed while
every message was dropped on the floor — a delivery path that looks wired and isn't. So
NOTIFICATIONS_DISABLED is set for Objecten in both compose files instead.
- ponytail ceiling: Objecten emits no notifications, so nothing downstream can react to a register write yet.
- Lifted by ADR-0029 (S-19b-1, #152): broker, worker,
objectenkanaal and notifications config now exist, andNOTIFICATIONS_DISABLEDisfalse.
Consequences
Positive
- The register is a first-class record with its own schema, lifecycle and query surface, independent of the case that produced it.
- The disclosure boundary is enforced by Objecten's schema validation (ADR-0027), not by discipline in projection code.
- The read projection can become a cache of Objecten rather than a re-derivation of ZGW (S-19b, #150).
Negative / costs
- Approval writes to two modules and is eventually consistent; a failure between them leaves a zaak in eindstatus without a register record until the approval is retried. Nothing repairs that automatically yet.
- One more upstream module on the approval path, and one more dev credential
(
Acl__Objecten__Token) in compose. - Two new hand-kept constants: the pinned objecttype UUID (two files) and the objecttype
name (compose +
register.py). - Until S-19b lands, the public register is still read from the NRC-derived projection, so the register record is written but not yet read — the two must agree.
Coupling rules touched (CLAUDE.md §8)
None bent. §8.1 is extended in spirit — the ACL is the only code that talks to Objecten, exactly as it is the only code that talks to ZGW. The domain still passes only a zaak URL, and no service reaches Objecten's database.
Verification
The end-to-end assertion lives in the Playwright happy path
(tests/e2e/registration.spec.ts, run by verify-e2e): after the behandelaar approves and
the openbaar register shows INGESCHREVEN, it asserts Objecten holds exactly one
RegisterRecord for that reference, with status INGESCHREVEN and no field outside the
public-safe schema.
It belongs there and not in verify-domain, which looks like the obvious home: that check
completes the Beoordelen task straight through Flowable REST (deliberately — it exists to
exercise the Workflow Client's REST contract), which bypasses the domain decide path that
calls the ACL. The e2e is the only check that drives a real approval.
ObjectenGatewayIntegrationTests (Category=Integration, so it runs under verify-acl
inside the compose network) drives the real gateway against a live Objecten + Objecttypen
pair: two writes for the same id leave exactly one object, carrying the second write's
status and nothing outside the public-safe schema.
All three findings above — the pinned UUID, the notifications block, and the base-URL constraint — came out of running the gateway against those live modules while writing the slice, not out of CI.