Start by clarifying requirements and scale, then design the API endpoints and data models. Walk through the core flows: joining a waitlist, detecting inventory availability, and notifying users. Emphasize fairness, concurrency, and scalability trade-offs.
Pro tip: Use a FIFO queue with idempotency keys for join requests, and consider a two-phase notification system (soft hold then confirm) to avoid race conditions when inventory opens.
Ask about expected traffic, listing/date cardinality, notification channels, and fairness guarantees. Establish read/write ratios and latency requirements.
Define RESTful endpoints for joining, leaving, and checking waitlist status. Model entities: WaitlistEntry, Listing, DateInventory, and Notification.
Select a datastore (e.g., Redis sorted sets for FIFO, or DynamoDB with composite keys). Explain how to maintain per-listing, per-date ordering and handle idempotency.
Use atomic operations or distributed locks to prevent double-booking. Design a notification service with retries and a soft-hold mechanism to manage inventory release.
Discuss sharding by listing/date, caching, and asynchronous processing. Compare push vs. pull notifications and explain consistency vs. availability trade-offs.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.