Sign in Get started

Distributed Systems for Backend Engineers · Capstone

Capstone: Multi-Region Inventory

Design inventory for a retailer selling in three regions.

Scenario

A retailer sells from warehouses in the US, EU and APAC. Product pages must load fast everywhere; overselling limited items (sneaker drops) is unacceptable; regular items can tolerate small oversell risk with backorders. A region outage must not stop sales in other regions.

Requirements

  • Fast reads globally
  • No oversell for limited items
  • Regional failure isolation
  • Accurate stock reporting

Constraints

  • Cross-region latency ≈ 100–200 ms
  • Drops: 50k users, 1k items, 2 minutes

Deliverables

  1. Choose consistency per operation and the data architecture.
  2. Explain failure behavior and reconciliation.

Draft each deliverable below before revealing the model answer and rubric.

Further reading: Designing Data-Intensive Applications

Deliverables

Choose consistency per operation and the data architecture.

Model answer

Stock is owned per warehouse region (home region per SKU-warehouse); reads served from local replicas/caches (eventual, fine for display). Regular items: reserve locally in the warehouse's region with conditional decrements; small oversell handled by backorders. Limited drops: route reservations to a single strongly consistent authority (one region or a distributed SQL table with serializable transactions) — users accept extra latency; virtual waiting room in front.

Rubric

Strong answers choose different consistency levels per operation and give limited items a single source of truth.

Explain failure behavior and reconciliation.

Model answer

Region outage: other regions keep selling their own warehouse stock; SKUs homed in the failed region show 'limited availability' (no cross-region writes without the owner) or fail over to a standby with RPO bounds. Events via outbox/CDC feed a global reporting view; nightly reconciliation compares warehouse counts with reservations; fencing tokens/leases if ownership moves between regions.

Rubric

Look for explicit partition-time behavior (CAP choice) and reconciliation.

Open in the app to mark lessons complete, take notes and track your progress.