Microservices Architecture for E-commerce Flow

1. Identified Microservices

For the given e-commerce user flow, the following microservices are identified based on core domain responsibilities, separation of concerns, and future scalability. Each microservice encapsulates a bounded context with its own data store and business logic.

1.1 Auth Service

• Responsibilities:

  • Validates user login credentials.
  • Mocks token/session generation.
  • Provides user identity to other services.

1.2 Product Service

• Responsibilities:

  • Maintains the catalog of products.
  • Allows querying products by name or category.
  • Provides detailed product information.

1.3 Cart Service

• Responsibilities:

  • Manages user shopping cart.
  • Adds/removes items and retrieves cart content.

1.4 Order Service

• Responsibilities:

  • Initiates order placement.
  • Validates cart contents.
  • Orchestrates inventory check and mock payment.
  • Manages order status transitions.

1.5 Inventory Service

• Responsibilities:

  • Maintains inventory stock levels.
  • Supports reserving and releasing stock.

1.6 Notification Service

• Responsibilities:

  • Sends/logs notifications based on order events.
  • Supports logging for audit purposes.

API Gateway

• Responsibilities:

  • Acts as the single entry point for external clients.
  • Routes requests to respective services.
  • Handles cross-cutting concerns (rate limiting, caching, load balancing).

---

2. API Endpoint Definitions

Auth Service

POST /auth/login
{
  "username": "john_doe",
  "password": "mock123"
}
Response:
{
  "token": "mock-jwt-token"
}

Product Service

GET /products?name=shoes&category=sports
Response: [ { product } ]

GET /products/{productId}
Response: { product }

Cart Service

• User id will be retrieved from access token provided in request header

POST /cart/add
{
  "productId": "prod-001",
  "quantity": 2
}
Response: { "message": "Product added to cart" }

GET /cart/
Response: { "userId": "user-123", "items": [ ... ] }

Order Service

POST /orders
{
  "cartId": "cart-123"
}
Response (success): { "orderId": "order-987", "status": "confirmed" }
Response (failure): { "status": "cancelled" }

Inventory Service

POST /inventory/check
{
  "productId": "prod-001", "quantity": 2
}

Notification Service (Internal)

I am using message broker for notification

publish events
{
  "userId": "user-123",
  "type": "order_success",
  "message": "Order confirmed."
}

---

3. Inter-Service Communication Approach

Style

• RESTful HTTP: All services communicate via RESTful HTTP APIs.
• Synchronous communication: Order Service calls Inventory and Notification services directly using http client.

Flow Example (Placing Order):

1. User adds product to cart via Cart Service.

2. User places order via Order Service:

   • Order Service calls Cart Service to get cart items.
   • Calls Inventory Service to check items availability.
   • Mocks payment logic.
   • If successful: creates order and calls Notification Service.
   • If failed: calls Notification Service with cancellation.

Assumptions:

• Authentication JWT based access
• Inventory system holds product ID and stock only (no full product info).
• Notification system is a logger (no real email/SMS integration).
• No orchestration tool like Saga or choreography; Order Service drives the transaction.
• Each microservice has its own database (In-memory).

---

4. High-Level Architecture Diagram (Textual Representation)

                       +-------------------+
                       |   API Gateway     |
                       +--------+----------+
                                |
       +------------------------+------------------------+
       |                        |                        |
+---------------+    +------------------+     +-------------------+
|  Auth Service |    | Product Service  |     |  Cart Service     |
+---------------+    +------------------+     +-------------------+
                                                   |
                                                   v
                                          +-------------------+
                                          | Order Service     |
                                          +-------------------+
                                           /         \
                                          v           v
                             +----------------+  +--------------------+
                             | Inventory Svc  |  | Notification Svc   |
                             +----------------+  +--------------------+

---

Docker images used

• GatewayService
• UserService
• ProductService
• CartService
• OrderService
• InventoryService
• PaymentService
• NotificationService

---

Boot Application

docker compose -f prod.docker-compose.yml up

Stop Application

docker compose -f prod.docker-compose.yml down

SEQ UI (Logging & Distributed Tracing)

Open http://localhost:8081

TODOS:

• Need to clear cart after order created
• Need to update inventory after payment successful
• Need to update order status after payment [success / failure]