Design an online ticket booking system
Company: Microsoft
Role: Software Engineer
Category: System Design
Difficulty: medium
Interview Round: Technical Screen
## System Design: Online Ticket Booking System
Design an online ticket booking system that allows users to discover events and book tickets.
Assume the product supports:
- Browsing/searching events (by city, venue, date, artist/category)
- Viewing seat maps (for seated venues) or selecting quantity (for general admission)
- Reserving seats during checkout to prevent double-sell
- Payment and confirmation
- Cancellations/refunds (optional but discuss)
### Requirements
#### Functional
1. Search and list events.
2. Show event details, pricing tiers, and seat availability.
3. Create an order:
- For seated events: choose specific seats.
- For GA: choose quantity.
4. Prevent overselling (strong consistency for inventory).
5. Support payment, then issue a ticket/QR code.
6. Send confirmation notifications (email/SMS/push).
#### Non-functional
- High read traffic (browsing) and bursty write traffic at on-sale time.
- Low latency for seat selection (e.g., p95 < 200–500ms for key APIs).
- High availability; graceful degradation when demand spikes.
- Strong correctness for inventory (no double booking).
- Auditability (payments, order state transitions).
### Scale assumptions (you may pick)
- Peak: 200k concurrent users during major ticket drops.
- Inventory per event: up to 100k seats.
Quick Answer: This question evaluates a candidate's proficiency in system design and distributed systems concepts, including scalability, availability, concurrency control, inventory consistency, low-latency API design, and operational concerns like payment auditability.