E-commerce Microservices Backend

Project roadmap

1. 01

   Define the service boundaries

   ~2h

   Write ARCHITECTURE.md: each service's responsibility, its own database (services never share tables), its REST endpoints, and the flow for placing an order, including what happens when reserving stock fails. Create a multi-module Maven or Gradle project with catalog-service, inventory-service, order-service, discovery-server and api-gateway. Done when: the document is complete, and every module builds.

2. 02

   Build the three services

   ~3h

   Catalog: CRUD for products (sku, name, price). Inventory: GET stock by sku and POST /reservations to reserve quantities for an order, refusing when there isn't enough stock, done in one transaction. Order: POST /orders with items, stored with a status. Give each service its own PostgreSQL database (or H2 during development) and validate the input. Done when: each service works on its own when called directly.

3. 03

   Add service discovery

   ~1.5h

   Create the discovery-server with @EnableEurekaServer. Register the three services as Eureka clients using their spring.application.name. Done when: the Eureka dashboard lists all three services, and starting a second copy of a service shows two instances.

4. 04

   Call between services

   ~2.5h

   In the order service, call the catalog to get current prices and the inventory to reserve stock, using a load-balanced WebClient or RestClient with service names (http://inventory-service) instead of addresses. Save the order as CONFIRMED when the reservation succeeds and REJECTED with the reason when there isn't enough stock. Set timeouts on every call. Done when: placing an order reduces the stock, and ordering too much is rejected.

5. 05

   Add the API gateway

   ~1.5h

   Configure Spring Cloud Gateway routes /api/products/** to catalog, /api/inventory/** to inventory and /api/orders/** to orders, using lb:// service names. Add a filter that attaches a request id header, logged by every service so one request can be followed across services. Done when: every endpoint works through the gateway's port, and logs show the same request id in each service.

6. 06

   Add a circuit breaker

   ~2h

   Wrap the order service's calls to inventory with a Resilience4j circuit breaker (through Spring Cloud CircuitBreaker) with a timeout and limited retries. When inventory is down or slow, fail quickly and return 503 with a clear message instead of making customers wait. Expose the breaker's state through Actuator. Done when: stopping inventory makes orders fail fast, and they work again automatically after it restarts.

7. 07

   Run everything with Docker

   ~2h

   Write a Dockerfile for each service and a docker-compose.yml running all of them plus their databases, with health checks and start-up order. Write an end-to-end test script: create a product, add stock, place an order through the gateway and check the stock decreased. Done when: docker compose up starts the whole system, and the script passes.

Resources

• DocsSpring Cloud Netflix (Eureka) reference
• DocsSpring Cloud Gateway reference
• DocsResilience4j CircuitBreaker
• ArticleMicroservices patterns (microservices.io)
• DocsDocker Compose documentation