I jumped straight into the physical stuff, like how many floors, spot types, sensors.
Start by clarifying requirements and scale, then design the data model for spots, reservations, and payments, and finally architect the system for high availability and consistency. Focus on trade-offs between consistency and availability, and how to handle concurrency and payment reliability.
Pro tip: Emphasize idempotency and exactly-once processing for payments, and discuss how you would handle edge cases like double-booking or payment failures with compensating transactions.
Ask about expected number of spots, daily transactions, peak load, and whether reservations are for specific spots or just guaranteed entry. Clarify payment methods, refunds, and integration with physical hardware.
Define entities: Garage, Spot, Reservation, Payment, User. Consider relationships, indexes, and how to represent availability and time slots. Discuss SQL vs NoSQL trade-offs.
Outline services: Reservation Service, Payment Service, Spot Management, Notification. Choose databases, caching, and message queues. Address scalability, fault tolerance, and consistency.
Explain how to prevent double-booking using optimistic locking, distributed locks, or transactions. Discuss consistency models (strong vs eventual) and their impact on user experience.
Detail the payment process: authorization, capture, refunds. Ensure idempotency, retries, and reconciliation. Discuss integration with external payment gateways and handling failures.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.