Chapter 10.1☕ 14 min read

Microservices Architecture Intro

In the real world, enterprise applications grow too large to fit in a single codebase. If the "Payment" module crashes, it shouldn't take down the "User Profile" module. <strong>Microservices</strong> break a giant app into small, independent services.

01The Concept: Monolith vs Microservices

The HITEC City IT Park Analogy:

Imagine a single massive building in HITEC City where all companies share the same electricity, water, and elevators. If a pipe bursts in the kitchen of Company A, Company B and C also get flooded and can't work. This is a Monolith.

Instead, the IT park is divided into separate buildings (Microservices). Building A handles Payments. Building B handles Users. They have their own electricity (databases). If Building A catches fire, Building B keeps working. They communicate by sending letters to each other over the road (Network API calls).

02Technical Explanation

Monolith: One big Spring Boot JAR containing all code and sharing one database.
Microservices: Multiple small Spring Boot apps. Each has its own database and runs on its own port.
Spring Cloud Config Server: A centralized server that holds application.properties for all microservices, so you don't hardcode passwords in every service.
Spring Cloud Release Train: For Spring Boot 3.2/3.3, you must use Spring Cloud 2023.0.x (Leyton). Old Netflix components like Zuul and Ribbon are completely removed.

03Full Working Code: The Microservices POM Setup

To build microservices, your parent pom.xml must import the correct Spring Cloud Bill of Materials (BOM).

pom.xml (Parent POM snippet)

<properties>
    <java.version>17</java.version>
    <spring-cloud.version>2023.0.1</spring-cloud.version>
</properties>

<dependencyManagement>
    <dependencies>
        <!-- Import the Spring Cloud BOM -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-dependencies</artifactId>
            <version>${spring-cloud.version}</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

In a real enterprise app, you would create separate projects: user-service (port 8081) and payment-service (port 8082).

04Why It Matters

Interview Question: "What are the main advantages and disadvantages of Microservices?"

Answer:
Advantages: Independent deployment (if payment fails, users still log in), independent scaling (scale only payment during a sale), and technology flexibility.
Disadvantages: High complexity (managing 10 servers instead of 1), network latency (services must talk over HTTP instead of in-memory method calls), and distributed debugging is hard.

05Interview Note

Enterprise Note: Never start a new project with microservices. Start with a well-structured Monolith. Only break it into microservices when the development team grows too large and the monolith becomes too slow to build/deploy.

Key Takeaways

✅ Microservices are independent services with their own databases, communicating via network
✅ Spring Cloud BOM (Bill of Materials) manages dependency versions across all services
✅ Spring Cloud 2023.0.x (Leyton) is the correct version for Spring Boot 3.x
✅ Netflix Zuul, Ribbon, and Hystrix are deprecated — do not use them

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