Start by clarifying the requirements and constraints, then propose a design centered on idempotency keys with a deduplication store that records request outcomes. Walk through the lifecycle of a request, covering key generation, storage, TTL, response replay, and concurrency control, and discuss trade-offs and failure modes.
Pro tip: Emphasize that idempotency is a contract between client and server: the client must generate and reuse keys, and the server must guarantee exactly-once side effects. Also, highlight the importance of handling partial failures and ensuring the dedup store is highly available and consistent.
Ask questions to understand the operations (payments, orders), expected retry patterns, consistency needs, and scale. Define what 'idempotent' means for the system and identify key constraints like latency and availability.
Explain how clients generate unique keys (e.g., UUIDs) and include them in requests. Discuss key format, validation, and how to handle missing or duplicate keys.
Choose a storage solution (e.g., Redis, DynamoDB) to store keys and associated responses. Describe the data model: key, status, response, timestamp, and TTL. Ensure atomic operations for check-and-set.
Use locks or conditional writes to prevent concurrent processing of the same key. Discuss how to handle out-of-order requests and ensure that only one request executes the side effect.
Set TTL based on business needs (e.g., 24 hours) to balance storage and retry window. On duplicate key, return the stored response (success or error) without re-executing. Discuss cleanup and monitoring.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.