Aggregate Downstream Services with Explicit Failure Policies

A frontend request reaches service A, which calls services B and C and returns an aggregate result. Design the request-handling and failure behavior, including when to fail open, when to fail closed, and how to retry. ### Constraints & Assumptions The source omits the detailed business semantics of B and C. Treat failure policy as a per-dependency decision based on its role; do not declare every downstream failure optional or every failure fatal. ### Clarifying Questions Which downstream results are required? Are calls reads or side effects? Can they run concurrently? What end-to-end deadline and partial-result contract apply? Is stale data acceptable? ### What a Strong Answer Covers Deadline propagation, bounded concurrency, cancellation, classified errors, safe retries, circuit breaking, and explicit partial-result semantics. ### Follow-up Questions Would you fail open for an authorization dependency? What if a side-effecting call times out after committing? How do retries across several service layers amplify load?