notandClaude Opus 5
fc843a419a
Records why the werkbak polls rather than being pushed to (proposal #163): nothing notifies the BFF either, so SSE/WebSockets would poll the domain inside the BFF for the same freshness plus connection state, a dependency and a stateful BFF. Names the ceiling (fixed 5s interval, per open page, keeps polling in a hidden tab) and the upgrade path (publish task events, then swap the interval for a stream). Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
80 lines
3.9 KiB
Markdown
80 lines
3.9 KiB
Markdown
# ADR-0032: The werkbak refreshes itself by polling, not by a pushed stream
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- **Status:** Accepted
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- **Date:** 2026-09-04
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- **Deciders:** Respellion engineering
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- **Slice:** #162 (proposal #163). The issue titles it S-26; that id already belongs to
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the self-service resume slice (#111), so #162 is the identifier that counts.
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## Context
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The werkbak (S-12) is a read of the open Flowable `Beoordelen` tasks: portal → BFF
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`GET /behandel/werkbak` → domain `Werkbak` query → workflow engine, each task enriched
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from its aggregate. A registration reaches `Beoordelen` **asynchronously**, only once the
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citizen supplies its documents and the DMN routes it (S-10a) — so it appears in a werkbak
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that is already open, and until now a behandelaar had to reload the page to see it.
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Three forces shape the mechanism:
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- **Nothing notifies anyone.** The trigger lives in Flowable. The domain does not publish
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task events, and there is no bus between the domain and the BFF.
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- **The BFF is stateless** and sits behind each portal's nginx.
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- **This is the repo's first live-updating view**, so the choice sets a precedent.
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## Decision
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**The werkbak page re-reads the existing BFF endpoint on a fixed interval
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(`WERKBAK_REFRESH_MS`, 5 s) while it is open. No new endpoint, dependency or server-side
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state.**
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The refresh is a *background* read: it leaves the rows and the loading/failure states
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untouched until it has an answer, so a tick never flashes a spinner over rows a
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behandelaar is reading and a single failed poll never swaps the list for the error alert.
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A read that comes back also clears an earlier failure, so the view recovers on its own —
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the same reload this slice set out to remove would otherwise be needed to escape a
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transient error. Only a foreground read (on open, after a decision) speaks for whether the
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werkbak is readable at all.
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### Why not SSE or WebSockets
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Neither buys freshness here, because **nothing notifies the BFF either**:
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- **SSE** (`text/event-stream`) would mean a new streaming endpoint whose handler polls the
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domain and forwards diffs — the same latency, plus connection lifecycle, nginx
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buffering, and auth on a long-lived connection.
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- **WebSocket/SignalR** adds a dependency (CLAUDE.md §13) and makes the BFF stateful and
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sticky-session-bound. A genuine push path would *also* need the domain to publish task
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events. Warranted by high-frequency, bidirectional or fan-out-heavy traffic; the werkbak
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is none of those.
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Polling meets the acceptance ("a registration can be seen in the werkbak once it is ready
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for review") in a handful of lines inside one component.
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- ponytail ceiling: a fixed 5 s interval, per open page, that keeps polling in a
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background tab. Each tick costs one Flowable task query plus a store read per open task.
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- Upgrade path: publish task events from the domain, then swap the component's `interval`
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for a stream. The endpoint contract and the component's rendering stay as they are;
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gate on `document.visibilityState` first if request volume is the concern.
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## Consequences
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**Positive**
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- The outcome is delivered with no new endpoint, dependency, or server-side state, and no
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service boundary moves.
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- Self-healing: a transient read failure no longer strands the view until a manual reload.
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- The e2e got *simpler* — the happy path waits for the werkbak row without reloading the
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page, which is itself the live-refresh assertion.
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**Negative / costs**
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- Staleness is bounded by one interval (≤5 s) rather than instant.
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- One `GET /behandel/werkbak` per open werkbak per interval, including in hidden tabs.
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- The precedent is polling; a future view with genuinely high-frequency updates will have
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to revisit this (see the upgrade path above).
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## Coupling rules touched (CLAUDE.md §8)
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None. The poll reuses the existing portal → BFF → domain read path: §8.3 (portals talk
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only to the BFF) and §8.2 (only the Workflow Client talks to Flowable) are unchanged.
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