springboot-microservices

Microservices Included:

• api-gateway
• discovery-server
• product-service
• inventory-service
• order-service
• notification-service
• k8s

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Database Selection: MongoDB for Product Service, MySQL for Inventory & Order Services

Why MongoDB for Product Service?

• Schema Flexibility: Allows storing varied product attributes (color, size, specifications, images) without strict schema constraints.
• High Read Performance: Optimized for product browsing and searching with fast querying and indexing.
• Scalability: Scales horizontally to handle large product catalogs efficiently.

Why MySQL for Inventory & Order Services?

• Relational Structure: Ensures ACID-compliant transactions, crucial for inventory and orders.
• Joins & Relationships: Handles relationships between users, products, and transactions effectively.
• Data Integrity & Consistency: Prevents stock inconsistencies and overselling with strict transactional support.

Hybrid Database Architecture Benefits

✅ Scalability & Flexibility: NoSQL (MongoDB) for unstructured product data, SQL (MySQL) for structured transactional data. ✅ Performance Optimization: MongoDB for fast product catalog queries, MySQL for transactional integrity. ✅ Consistency vs. Availability: MySQL prioritizes consistency (inventory/orders), MongoDB prioritizes availability (products).

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API Gateway

An API Gateway acts as a single entry point for routing client requests to backend services, offering load balancing, security, and monitoring.

Why Use API Gateway?

• Routing: Directs requests to appropriate microservices.
• Security: Manages authentication & authorization.
• Load Balancing: Distributes requests among instances.
• Rate Limiting: Prevents excessive API usage.
• Monitoring & Logging: Captures request/response data.
• Protocol Translation: Supports REST, WebSocket, and other protocols.

Advanced Features of Spring Cloud Gateway

• Authentication & Authorization: Integration with Spring Security or JWT.
• Rate Limiting: Controls request frequency.
• Circuit Breaker: Uses Resilience4j for fault tolerance.
• Service Discovery: Integrates with Eureka for dynamic routing.

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Discovery Server (Eureka)

Role in Microservices Architecture

• Eureka Server: Acts as a service registry for dynamic service discovery.
• Eureka Client: Registers services and discovers other services dynamically.

Benefits of Service Discovery

• Eliminates hardcoded service URLs.
• Enables dynamic scaling of microservices.
• Improves fault tolerance and resiliency.

URL Differences with Eureka

Scenario	URL Used in Order Service
Without Eureka	http://localhost:8082/api/inventory
With Eureka	http://inventory-service/api/inventory

Key Benefit: With Eureka, service URLs remain unchanged even if the service moves to another port or machine.

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Product Service

Database Used: MongoDB

• Stores product data efficiently with a flexible schema.
• Optimized for read-heavy operations.

Key Properties Stored:

• id
• name
• description
• price

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Inventory Service

Database Used: MySQL

• Ensures transactional integrity for inventory stock management.
• Supports relational queries for inventory tracking.

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Order Service

Database Used: MySQL

• Guarantees ACID compliance for order transactions.
• Supports complex relationships between users, products, and transactions.

Fault Tolerance with Resilience4j

• Circuit Breaker: Prevents system failures by falling back to an alternative method.
• Time Limiter: Ensures time-bound execution.
• Retry Mechanism: Automatically retries failed requests.

Kafka Integration

• Uses Kafka for event-driven communication.
• Sends order placed events to a notificationTopic.

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Monitoring & Health Checks

Actuator Prometheus Endpoint

• Enables Prometheus endpoint for monitoring application metrics.
• Exposes system metrics like memory usage, CPU load, and request count.

Health Management Properties

• Enables circuit breaker health monitoring.
• Configures endpoint exposure for system monitoring.