Design an online ticket booking system

Q: Design an online ticket booking system

This is a System Design interview question from Microsoft for Software Engineer roles. View the full question and solution on PracHub.

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Question

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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

Search and list events.
Show event details, pricing tiers, and seat availability.
Create an order:
- For seated events: choose specific seats.
- For GA: choose quantity.
Prevent overselling (strong consistency for inventory).
Support payment, then issue a ticket/QR code.
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.