Capstone: a resilient service

P38.services.02 · Audience: guest, it-ml, language-pro · Prerequisites: APIs & service design, Monolith vs microservices & distributed basics

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A real service never gets to practise one skill at a time: the request that needs a clean seam to test against is the same request that must survive a retry and a flaky dependency. That is why this capstone asks for all of P38 at once. You'll build a small order service that is well-architected (its store arrives as an injected port), correct under retries (idempotent by key), and resilient (it retries a flaky dependency with backoff). It's the kind of service you'd package (P35), gate in CI (P36), and make observable (P37) — the whole pillar converging on one artefact.

Step 1 / 2 — Three ideas, one service
ⓘ Concept: Architected + idempotent + resilient
The service depends on a persistence port (injected, not constructed) — that's the architecture. It's idempotent by key, so a retried request creates one order. And it retries the store's transient failures with backoff, surfacing a permanent failure rather than dropping it. Each is a P38 idea; together they're a service you can trust.

Why it matters — Real services need all three at once: a clean seam to test against, exactly-once effects under retries, and survival of transient failures — this is where they combine.

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🎓 Practice ladder

1 graded rung · ~40 min

Build a resilient, idempotent order service over an injected store — graded by hidden tests and a design rubric.

Capstone — a resilient service (project)

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That's the production discipline in miniature — architected, correct, and resilient. The remaining track zooms out to where these services live: distributed systems.

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Capstone: a resilient service — TransformerLab