Design a booking system
Company: Airbnb
Role: Software Engineer
Category: System Design
Difficulty: medium
Interview Round: Onsite
Design an online booking system (e.g., for hotel rooms, meeting rooms, or appointment slots).
### Requirements
Cover the following in your design:
- **Core flows**: search availability, create booking (reserve), confirm, cancel, modify.
- **Correctness**: prevent double-booking under high concurrency.
- **Scale**: support many users and a large inventory (properties/rooms/slots).
- **Latency**: fast availability queries.
- **Reliability**: handle retries, partial failures, idempotency.
### Clarifications to address
- What consistency guarantees are needed for availability and booking creation?
- Do you need a “hold” (temporary reservation) with expiration?
- How do you model inventory (per day, per time slot, per resource)?
Provide APIs, data model, and a high-level architecture, and discuss tradeoffs.
Quick Answer: This question evaluates system design skills including distributed systems, data modeling, concurrency control, consistency models, API design, scalability, low-latency querying, and reliability for transactional booking flows.