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Microservices

Microservices architecture is a software design approach where an application is structured as a collection of small, independent services that communicate over well-defined APIs. Each service is focused on a specific business capability and can be developed, deployed, and scaled independently.

Key Characteristics of Microservices Architecture​

  1. Independently Deployable Services: Each microservice is self-contained and can be deployed without affecting others.
  2. Decentralized Data Management: Every service has its own database or data source to prevent data coupling.
  3. Technology Agnostic: Different services can be written in different languages and use different data stores.
  4. Service Communication via APIs: Services communicate with each other using lightweight protocols like HTTP/REST or messaging queues (e.g., RabbitMQ, Kafka).
  5. Domain-Driven Design (DDD): Services are modeled around business domains (bounded contexts).
  6. Scalability and Resilience: Individual services can scale horizontally, and if one fails, others continue to function.
  7. DevOps & CI/CD Friendly: Microservices enable continuous integration and deployment because services are small and isolated.

Architecture Diagram​

   [ API Gateway ]
        /   |   \
 [User Service] [Product Service] [Order Service]
       |            |                 |
   [User DB]   [Product DB]       [Order DB]

Example​

  1. User Service

    • Handles registration, login, profile.
    • Owns UserDB.
    • Exposes APIs like:
      • POST /users/register
      • GET /users/{id}

  2. Product Service

    • Manages products, categories, inventory.
    • Owns ProductDB.
    • Exposes APIs like:
      • GET /products
      • POST /products/add

  3. Order Service

    • Handles orders, checkout, payments.
    • Owns OrderDB.
    • Exposes APIs like:
      • POST /orders/create
      • GET /orders/{userId}

  4. API Gateway

    • Entry point for clients (web/mobile).
    • Routes requests to the appropriate service.
    • Can handle authentication, rate-limiting, and logging.

How It Works Together​

  1. A user registers via the API Gateway, which forwards the request to the User Service.

  2. The user adds items to a cart (frontend logic), and when checking out:

    • Product Service is queried for item availability.
    • Order Service processes the order and stores it in OrderDB.
    • Payment is handled via a third-party or separate Payment Service.

Advantages of Microservices Architecture​

  • Scalability: Scale services independently.
  • Resilience: Failure in one service doesn't crash the whole system.
  • Flexibility: Use best-fit technologies for each service.
  • Faster Development: Teams can work on services in parallel.
  • Easier Maintenance: Smaller codebases per service.

Challenges​

  • Complex Deployment: Managing many services is harder than a monolith.
  • Data Consistency: Harder to maintain ACID properties across services.
  • Distributed Debugging: Tracing bugs across services can be tough.
  • Network Latency & Failures: Inter-service calls introduce overhead.

Technologies Commonly Used​

  • Service Communication: REST, gRPC, GraphQL, Kafka, RabbitMQ
  • Service Discovery: Eureka, Consul, Kubernetes DNS
  • API Gateway: NGINX, Kong, AWS API Gateway
  • Containerization: Docker, Kubernetes
  • Monitoring: Prometheus, Grafana, ELK Stack
  • CI/CD: Jenkins, GitHub Actions, GitLab CI