Module 12 Activity

Scenario

Make the boundaries you do not control fail in ways your callers can act on.

What you build

Per-request sessions, mapped boundary failures, timeouts everywhere and bounded retries.

Steps

1. Make the database session a per-request dependency using yield and finally, and prove every session opened is closed.
2. Map every boundary exception to a specific status. Confirm none reaches the client as a 500.
3. Set an explicit timeout on every outbound call, shorter than any gateway in front of you.
4. Bound your retries, add jitter, and confirm no 4xx is retried.
5. Confine every query to the repository layer and confirm services import no driver.
6. Test one service with a fake repository and no database at all.

Evidence to hand in

• The session dependency with the open/close proof.
• The exception-to-status map.
• Timeouts on every outbound call.
• The retry policy with jitter and the retryable set.
• The service test with a fake repository.

Review checklist

• Every session is closed, including on the error path.
• No boundary failure reaches the client as a 500.
• Every outbound call has an explicit timeout.
• No 4xx is retried, and retries carry jitter.
• At least one service is tested with no database.

Mark complete