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Design a coffee ordering system

SalesforceSoftware Engineer · Technical Screen
MediumSoftware EngineerTechnical ScreenSystem Design

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This question evaluates system design competency, focusing on order lifecycle modeling and state-machine enforcement, idempotency and data consistency, event-driven integration, real-time status propagation, and scaling across stores.

System Design: Coffee Ordering System

Design a system for a coffee shop (or chain) that supports ordering drinks.

Core use cases

  • Customer browses menu and places an order (pickup or in-store).
  • Customer customizes items (size, milk type, add-ons) and sets quantity.
  • System calculates total price (including tax/discounts).
  • Payment can be processed (or order marked as pay-at-store).
  • Baristas see a queue of incoming orders and update status: PLACED → PAID (optional) → IN_PROGRESS → READY → COMPLETED/CANCELLED.
  • Customer can see order status updates.

Constraints / scale (assume)

  • Start with one store, then extend to many stores.
  • Peak: thousands of orders/min across all stores.
  • Status updates should feel near-real-time to customers.

What to cover

  • APIs (or events) for placing orders and status updates.
  • Data model for menu, orders, payments.
  • High-level architecture and major services.
  • Consistency, idempotency, and failure handling (e.g., retries, duplicate submits).
  • How you would scale to many stores.