Design a Rotating Workplace Food-Ordering Service

Scenario

Design an internal food-ordering platform for corporate campuses (similar to services like Fooda or Cater2.me). Each corporate office features a rotating lineup of external partner restaurants every business day. Employees can browse menus, customize dishes (e.g., dressings, protein choices), and place orders before a daily cutoff window. Orders must handle company meal subsidies alongside personal payment methods, while preventing race conditions when limited inventory items sell out during checkout.

Requirements

Functional Requirements

• Daily Vendor Rotation: Admins schedule partner restaurants to office locations days or weeks in advance. Employees can only view and order from vendors active at their assigned office for a selected date.
• Customizable Menus: Items support modifier groups (e.g., choice of protein, extra toppings, dressing on the side), where each modifier can alter the base price and item availability.
• Inventory & Safe Checkout: Certain items or modifiers have strict quantity caps per day. The system must prevent overselling when multiple employees check out simultaneously.
• Split Payment & Subsidies: The system applies an employer-provided daily stipend (e.g., $15/day). If the order total exceeds the stipend, the user's secondary payment method covers the remainder.
• Order Aggregation & Cutoff: Orders lock at a defined cutoff time (e.g., 10:30 AM), after which consolidated batch orders are dispatched to the restaurants.

Non-Functional Requirements

• Consistency over Availability at Checkout: Inventory reservation and payment processing must be strongly consistent to avoid overselling.
• High Read Availability: Menu browsing should have low latency (< 100ms p95) and survive temporary backend spikes right before cutoff.
• Fault Tolerance: Third-party payment failures or timeouts must leave order states clean and release reserved inventory.

Scale & Assumptions

• 50 corporate office locations; 50,000 daily active users (DAUs).
• Peak traffic: 70% of orders occur in the 60 minutes prior to the 10:30 AM cutoff (~10 orders/sec average, peaking at 50-100 orders/sec).
• Each office hosts 3 to 5 rotating restaurants per day, with each restaurant offering 20 to 40 items.

Key Deliverables

1. Data Model: Entities for offices, rotating schedules, menus, modifiers, inventory stock, and orders.
2. API Design: Key endpoints for fetching daily menus, reserving cart items, and completing checkout.
3. Concurrency & Inventory Management: Strategy to prevent double-allocation of limited meals during checkout surges.
4. Payment Flow: Handling two-phase payment (subsidy deduction + credit card charge) with proper rollback mechanics.