System Design Overview

Architecture Components

• API Gateway: Exposes a REST endpoint (POST /orders) for order creation

• Order Service (Lambda): Validates input, calculates the total, and creates an order record

• SNS Topic (OrderEvents): Publishes order events to trigger subsequent processes

• Invoice Service (Lambda): Subscribed to the SNS topic; generates an invoice upon receiving an order-created event

• Billing Service (Lambda): Listens for invoice events and processes the payment via a 3rd-party provider

• Shipment Service (Lambda): Triggered after payment confirmation to arrange shipment and retrieve a tracking number

• Email Service (Lambda): Subscribes to various events to send customer notifications (order received, invoice issued, payment processed, shipment dispatched, etc.)

          +--------------+
          |   Customer   |
          +------+-------+
                 |
                 v
         +---------------+
         |  API Gateway  |  (POST /orders)
         +-------+-------+
                 |
                 v
       +-------------------+
       |   Order Service   |  (Lambda)
       | - Validate order  |
       | - Calculate total |
       | - Persist order   |
       +--------+----------+
                |
                v
       +-------------------+
       |     SNS Topic     | (OrderEvents)
       +--------+----------+
                |                  
   +------------------+---------------+----------------+
   |                  |               |                |
   v                  v               v                v
  +--------------+ +--------------+ +--------------+ +--------------+
  |   Invoice    | |   Billing    | |   Shipment   | |   Email      |
  |   Service    | |   Service    | |   Service    | |   Service    |
  |  (Lambda)    | |   (Lambda)   | |   (Lambda)   | |   (Lambda)   |
  +--------------+ +--------------+ +--------------+ +--------------+
  

Overview

The system is built as an event-driven microservices architecture using AWS Lambda and SNS. It decouples responsibilities into several services:

Order Service: Exposes a REST API via API Gateway that accepts order requests. It validates input, calculates totals, creates an order, and publishes an event (status: ORDER_CREATED) to an SNS topic.

• Invoice Service: Triggered by the order event, it generates an invoice and publishes an invoice event (status: INVOICE_CREATED).
• Billing Service: Listens for invoice events and simulates payment processing. On success, it publishes a payment event (status: PAYMENT_CONFIRMED); on failure, it publishes an error event (status: PAYMENT_FAILED).
• Shipment Service: Receives payment events. If the payment is confirmed, it simulates shipment creation (generating a tracking number) and publishes a shipment event (status: SHIPPED). If shipment fails, it publishes an error event ( status: SHIPMENT_ERROR).
• Email Service: Listens for various events (order, invoice, payment, shipment, or error events) and sends email notifications to the customer at each stage or in case of errors.