# Build a Dual Fixed-Window Rate-Limiting Middleware Design FastAPI middleware that enforces both a global limit of 100 requests per minute and a per-domain limit of 3 requests per second. A request is accepted only when both counters have capacity. ### Constraints & Assumptions - Fixed windows use a server clock and deterministic window IDs. - Concurrent requests must not overshoot either limit. ### Clarifying Questions to Ask - Which request field defines the domain? - Do rejected requests increment counters? ### What a Strong Answer Covers - Atomic check-and-increment, keys, expiry, and response metadata. - Multi-worker correctness and boundary tests. ### Follow-up Questions - How would sliding windows differ? - How should dependency failure behave?