Design a food ordering and delivery system

Design a backend system for a food ordering + delivery platform (like a marketplace that connects customers, restaurants, and delivery couriers).

Core user flows

1. Customer:
   • Browse/search restaurants and menus
   • Add items to cart, place an order, pay
   • Track order status (prep, picked up, arriving)
2. Restaurant:
   • Receive order, accept/reject, update prep status
3. Courier:
   • Receive delivery offers, accept, pickup, deliver

Requirements

Functional

• Restaurant/menu discovery (basic search/filter is enough)
• Order creation and payment intent
• Reliable order state machine (created → accepted → preparing → ready → picked_up → delivered/cancelled)
• Dispatch: assign courier to an order
• Real-time-ish tracking and status updates to customer

Non-functional

• High availability (avoid single points of failure)
• Consistent order state (no double-deliver, no lost orders)
• Handle peak traffic (lunch/dinner bursts)
• Observability: metrics, logs, tracing

Deliverables

• APIs (high level)
• Data model (high level)
• Architecture and major components
• Approach to scaling, reliability, and failure handling (explicitly call out single points of failure)
• Consistency model choices and trade-offs