Designing an E-Commerce Platform

An e-commerce platform needs to handle product browsing, cart management, checkout, payments, and order fulfillment.

Services

┌─────────────────────────────────────┐
│           API Gateway               │
└────┬──────┬──────┬──────┬───────────┘
 Product  Cart  Order  Payment  User
  Svc     Svc   Svc    Svc     Svc

Product Catalog

• Storage: Elasticsearch (fast search + filters)
• Images: S3 + CDN
• Cache: Redis for top 10K products

Shopping Cart

• Store in Redis (fast, TTL = 7 days)
• Schema: cart:{user_id} → {product_id: qty, ...}

Inventory Management

Critical: Prevent overselling.

SOLUTION: Optimistic Locking
UPDATE inventory
SET quantity = quantity - 1
WHERE product_id = ? AND quantity > 0

For flash sales: Use Redis atomic DECR.

Checkout Flow

1. Reserve inventory
2. Create order (Pending)
3. Process payment
4. Confirm order
5. Release/deduct inventory
6. Notify user

Use Saga pattern to handle failures at each step.

Payment Processing

• Never store card data (PCI compliance)
• Integrate Stripe/PayPal via API
• Idempotency keys prevent double charges

Search

Elasticsearch with faceted filters:

• Category, price range, brand, ratings

Conclusion

E-commerce requires ACID transactions for payments, eventual consistency for catalog/reviews, and Redis for cart/inventory under high load.