Answer Key: Idempotency Patterns

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Exercise 1: Implement Idempotency

Question: Implement idempotency for an API. What pattern?

Answer

Idempotency Pattern: - Idempotency keys: Client generates unique keys - Key storage: Server stores processed keys - Deduplication: Check key before processing - TTL: Expire keys after TTL

Answer: Use idempotency keys, store processed keys, check before processing, expire after TTL.

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Exercise 2: Handle Duplicates

Question: Your system receives duplicate requests. How do you handle them?

Answer

Duplicate Handling: 1. Extract key: Extract idempotency key from request 2. Check storage: Check if key already processed 3. Process or return: Process if new, return cached if duplicate 4. Store result: Store result for duplicate requests

Answer: Extract key, check storage, process or return cached result, store for duplicates.

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Exercise 3: Design Keys

Question: Design idempotency keys for a payment system. What's the format?

Answer

Key Design: - Format: {client_id}:{request_id}:{timestamp} - Uniqueness: Ensures uniqueness per client - Context: Includes request context - TTL: 7 days (payment retention period)

Answer: {client_id}:{request_id}:{timestamp} format, unique per client, 7-day TTL.