Designing Microservices Architecture With a Custom Spring Boot Starter and Auto-Configuration Framework

Spring Boot has  Java development with its embedded servers, auto-configuration, and convention-over-configuration philosophy. Among its many features, one of the most powerful — but often underused — is the ability to create custom Spring Boot starters. These components enable development teams to package and reuse common configuration and boilerplate logic, making microservices more modular, maintainable, and consistent across a large-scale enterprise platform.

This article explores how to build and use custom Spring Boot starters with auto-configuration to centralize concerns such as database access, authentication, and WebSocket communication, especially valuable in environments like loan servicing and trading platforms that operate with numerous microservices.

Why Use a Custom Starter?

In any microservices-based system, many functional concerns repeat across services:

• Database connectivity
• Security configurations (e.g., JWT, OAuth2)
• Exception handling
• WebSocket communication
• Health checks and monitoring

Traditionally, developers either duplicate configuration files or share utility libraries to handle these recurring needs. However, this approach leads to fragmented configurations and tightly coupled services.

Custom Spring Boot starters allow you to extract and modularize this functionality. Instead of duplicating setup logic, you can include a starter dependency and configure only what’s unique to the microservice. The benefits include:

• Cleaner codebase: Each microservice focuses purely on business logic.
• Faster onboarding: New services go live with minimal setup.
• Consistency: Uniform application of security, logging, and monitoring policies.
• Centralized maintenance: Updates to shared logic are propagated via version bumps.

Project Structure

To illustrate, let’s assume you’re designing a loan servicing and trading platform. Here's how you might structure your Spring Boot-based framework:

loans-framework/

│

├── loans-starter-db/          # Custom DB configuration starter

├── loans-starter-security/    # JWT and OAuth2 setup

├── loans-starter-websocket/   # WebSocket endpoints and config

├── loans-core-service/        # Sample microservice using above starters

Each module serves a clear purpose:

• loans-starter-db handles JPA configuration, datasource bean creation, and repository setup.
• loans-starter-security provides authentication filters, JWT decoding logic, and security context management.
• loans-starter-websocket manages message brokers, STOMP endpoints, and topic subscriptions.
• loans-core-service is a business-specific microservice that leverages the above starters for its infrastructure.

This separation enforces modular design and supports easy scaling as new services are added.

Creating a Custom Starter

Let’s walk through building loans-starter-db, a custom Spring Boot starter for JPA database access.

Step 1: Create the Starter Module

Define the Maven artifact:

<artifactId>loans-starter-db</artifactId>

<packaging>jar</packaging>

Include relevant Spring dependencies:

<dependency>

  <groupId>org.springframework.boot</groupId>

  <artifactId>spring-boot-starter-data-jpa</artifactId>

</dependency>

Do not hardcode versions — inherit from a parent POM to maintain alignment.

Step 2: Add Auto-Configuration

Create an auto-configuration class using Spring annotations:

@Configuration

@ConditionalOnClass(DataSource.class)

@EnableJpaRepositories(basePackages = "com.loans.common.repository")

public class DatabaseAutoConfiguration {

 

  @Bean

  @ConditionalOnMissingBean

  public DataSource dataSource(DataSourceProperties properties) {

    return DataSourceBuilder.create()

         .url(properties.getUrl())

         .username(properties.getUsername())

         .password(properties.getPassword())

        .build();

  }

}

• @ConditionalOnClass ensures the configuration is only applied if DataSource is available.
• @ConditionalOnMissingBean allows services to override this bean if needed.
• @EnableJpaRepositories automatically scans for JPA repositories in the specified package.

Step 3: Register the Configuration

In src/main/resources/META-INF/spring.factories, declare your config:

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\

com.loans.dbstarter.DatabaseAutoConfiguration

This file tells Spring Boot to pick up your auto-configuration during the application startup phase.

Using the Starter in a Microservice

In loans-core-service, include the dependency:

<dependency>

  <groupId>com.loans</groupId>

  <artifactId>loans-starter-db</artifactId>

</dependency>

Then, configure only the database credentials in application.yml: 

spring:

  datasource:

    url: jdbc:postgresql://localhost:5432/loans

    username: user

    password: secret

You no longer need to configure JPA manually — the starter handles everything.

Extending to Other Concerns

Following the same approach, you can build additional starters:

Security Starter (loans-starter-security)

• Configures a JWT filter chain.
• Loads public key for token validation.
• Provides global exception handling for security failures.

WebSocket Starter (loans-starter-websocket)

• Defines STOMP endpoints.
• Configures message brokers (e.g., RabbitMQ).
• Sets up channel interceptors and listeners.

These components keep your services clean and focused on business capabilities while offloading platform concerns to reusable, tested modules.

Platform-Wide Benefits

Best Practices

• One responsibility per starter: Don’t combine DB, security, and WebSocket logic into one.
• Use a parent POM: Align versions across all modules to avoid conflicts.
• Publish to a private repository: GitHub Packages or Nexus works well.
• Add logging in auto-config classes: This aids debugging when beans aren’t loading as expected.
• Document everything: Provide sample usage, config options, and default behaviors.

Testing Before Production

Before releasing a starter, create integration test services that:

• Verify that all beans load correctly.
• Confirm that service-level overrides still work.
• Ensure that properties are bindable and follow expected naming conventions.

Include documentation or onboarding guides so that internal teams can adopt starters with minimal friction.

Conclusion

Custom Spring Boot starters are essential for teams managing distributed microservices at scale. They encapsulate shared logic, enforce consistent practices, and enable rapid, reliable service creation. By investing in a modular, auto-configurable architecture, engineering teams can unlock both speed and quality in their software delivery process.

GitHub example: https://github.com/ggajwani9/loans-framework.