Design a Food Delivery Cart
Company: Uber
Role: Software Engineer
Category: System Design
Difficulty: medium
Interview Round: Onsite
Design the cart subsystem for a food delivery platform similar to Uber Eats.
The cart should let users:
- add, update, and remove items
- choose item customizations and add-ons
- apply promotions or coupons
- see taxes, fees, and subtotal updates
- persist the cart across mobile and web sessions
- proceed to checkout with a consistent cart snapshot
Assume a cart usually contains items from only one restaurant at a time. The system should also handle menu changes, item unavailability, restaurant open or closed status, and price revalidation during checkout.
Discuss functional requirements, APIs, data model, storage choices, caching, consistency, scaling, and failure handling.
Quick Answer: This question evaluates competency in designing stateful, user-facing subsystems including data modeling, API design, session persistence, caching, consistency, transactional integrity, scaling, and failure handling for cart and checkout workflows.