Start by clarifying requirements and constraints (e.g., scale, consistency, supported payment methods) before diving into the design. Then propose a high-level architecture that abstracts upstream processors, ensuring idempotency, reliability, and security. Finally, discuss trade-offs and how you would handle failures and scaling.
Pro tip: Emphasize idempotency and exactly-once processing as critical for payment systems, and mention how you would handle partial failures and reconciliation with upstream processors.
Ask questions to understand scale, latency, consistency needs, supported payment methods, and compliance requirements. This ensures the design meets the actual needs.
Outline the main components: API gateway, payment service, processor adapters, database, and message queue. Explain how they interact to process a payment.
Detail the payment authorization, capture, and refund flows, including idempotency, retries, and error handling. Discuss how to ensure data consistency across services.
Discuss trade-offs between consistency and availability, choice of database, and how to scale horizontally. Mention monitoring, alerting, and reconciliation with upstream processors.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.