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Design an Event Booking System

MicrosoftSoftware Engineer · Onsite
MediumSoftware EngineerOnsiteSystem Design

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This question tests the ability to design a high-concurrency booking system, focusing on preventing double-bookings, managing seat availability, and ensuring atomic transactions.

Problem Statement

Design a scalable Event Booking System (e.g., for concerts or theater tickets) that allows users to browse events, select specific seats, and complete purchases.

Functional Requirements

  • Users can view a list of events and their corresponding venue maps.
  • Users can reserve specific seats for a limited time (e.g., 10 minutes) before completing the payment.
  • Users can complete the purchase to finalize the booking.
  • Once a seat is purchased, it must be marked as unavailable to other users.

Non-Functional Requirements

  • High availability and scalability during peak traffic (e.g., ticket drops).
  • Strong consistency for seat inventory: no two users should be able to book the same seat.
  • Low latency for seat selection and checkout processes.

Deliverables

  1. High-level architecture diagram (describe the components).
  2. API design for seat selection and booking.
  3. Data model (schema overview for Events, Seats, and Bookings).
  4. Concurrency strategy: How do you handle the 'race condition' when two users click 'Book' on the same seat at the same time?
  5. Failure handling: What happens if a user abandons the checkout process?

Hints

Hint 1

Consider using a distributed locking mechanism or optimistic concurrency control on the database row to prevent overbooking.

Hint 2

Decouple the seat reservation from the actual payment processing to ensure the system remains responsive under heavy load.

Hint 3

Implement a TTL (time-to-live) mechanism, such as a background task or a cache expiry, to release held seats if payment is not finalized.

Follow-up questions

  • How would you handle a sudden traffic spike where 100,000 users are trying to book 5,000 seats simultaneously?
  • If the payment gateway API is down, how do you ensure the system remains consistent and provides a good user experience?
  • How would you implement a 'Waiting Room' or queueing system to manage traffic during high-demand event releases?