##### Question Pick one of your recent, non-trivial projects and conduct a deep, end-to-end technical review. The interviewer will probe each layer, so be ready to whiteboard the system and defend your decisions. Address all of the following: 1. **Architecture diagram.** Draw the end-to-end architecture: components, data stores, and the interfaces (REST/gRPC/streaming/WebSocket) between them. 2. **Data flow and invariants.** Explain the major data flows and state the key correctness invariants the system must preserve (e.g. "exactly one active assignment per order"). 3. **Read and write paths.** Walk through the concrete read path and write path step by step, including caching, idempotency, and the latency budget for each. 4. **Data and storage.** Describe the schema design and justify your storage choices (relational vs. NoSQL vs. cache vs. time-series/cold store), including partition/shard keys and indexes. 5. **Design decisions and trade-offs.** Justify your major technology choices and call out the trade-offs you accepted (consistency vs. availability, push vs. poll, write-through vs. write-behind, etc.). 6. **Scalability, bottlenecks, and capacity planning.** Give back-of-the-envelope numbers (QPS, message rates, storage), identify the bottlenecks, and explain how you'd capacity-plan for them. 7. **Consistency and reliability.** Explain your consistency model, delivery guarantees, and reliability strategies (retries, idempotency, sagas, circuit breakers, DR/RPO/RTO). 8. **Security and access controls.** Cover authN/authZ, service-to-service security, encryption in transit/at rest, PII handling, and compliance. 9. **Observability and SLAs/SLOs.** Describe your logs, metrics, and traces, and define concrete SLIs/SLOs and the alerts/runbooks that back them. 10. **A significant incident or trade-off you handled.** Describe a real production incident or hard trade-off decision, the root cause, and how you mitigated it. 11. **Two concrete improvements for a 10× traffic increase.** Propose two specific changes that would let the system absorb 10× traffic, and quantify why they work. 12. **What you would redesign today and why.** With hindsight, what would you change about the original design? Use concrete numbers and real examples from your project; avoid hand-waving.