E-commerce Integration Architecture: Orders, Stock, Shipping, and COD

Integration design starts with ownership. Which system owns the customer, which owns available stock, and where may order status change? Without these answers, the connection becomes a chain of conflicting copies.

When an order is created, the business system needs a unique channel reference, items, quantities, prices, discounts, address, and payment method. Receipt does not mean acceptance; there must be an explicit state for invalid items, prices, addresses, or duplicates.

Inventory synchronisation needs a rule that prevents overselling without flooding channels with unnecessary updates. Available stock is normally published after reservations, with defined latency and retry behaviour.

Shipping introduces picked, packed, handed-over, delivered, failed, and returned states. Every system needs clear authority over the states it can change and the way proof of delivery or failure reasons return.

For COD, delivery is not final collection. Reconciliation should connect shipment, collected amount, fee or difference, and transfer date. Otherwise revenue appears while cash has not arrived.

Test exceptions before the happy path: duplicate order, insufficient stock, invalid address, failed delivery, partial return, and COD difference. That is where architecture quality becomes visible.