Spring Boot Microservice Starter - Kafka + Hexagonal + Jooq

Project Title Options:

1. Kotlin Microservices & Hexagonal Architecture: A Hands-On Learning Project
2. Master Modern Backend Development: Spring Boot, Kafka, Jooq & Hexagonal Design
3. The Complete Microservice Starter: Kotlin, Kafka, Jooq & Hexagonal Architecture
4. Build & Deploy Scalable Microservices: A Practical Guide with Kotlin & Kafka

Project Description:

Unlock the power of modern backend development with this comprehensive, hands-on starter project! Dive deep into building two interacting microservices (product-backend and category-backend) using a cutting-edge stack: Kotlin, Spring Boot, Kafka for event-driven communication, Jooq for type-safe SQL with PostgreSQL, and the robust Hexagonal (Ports and Adapters) Architecture. This isn't just code; it's a launchpad for understanding and implementing real-world microservice patterns.

Who Is This For?

• Aspiring Backend Developers: Get a practical introduction to building sophisticated services.
• Java Developers: Transition smoothly to Kotlin and modern Spring Boot practices.
• Software Engineers: Learn or solidify knowledge of microservices, hexagonal architecture, and event-driven systems.
• Students & Self-Learners: Bridge the gap between theory and practical application with a well-structured project.
• Architects & Tech Leads: Explore a clean, maintainable, and scalable architectural template.
• Anyone curious about:
  • Implementing Hexagonal Architecture in a Spring Boot application.
  • Using Jooq for database interactions in Kotlin.
  • Integrating Kafka for asynchronous messaging between services.
  • Building and running multi-service applications with Docker Compose.

What Learners Will Gain:

This project provides a rich learning experience, enabling you to:

1. Master Hexagonal Architecture (Ports & Adapters):
   • Understand the "Why": Grasp the benefits of separating business logic (domain) from application (use cases) and infrastructure concerns (adapters for API, DB, Kafka).
   • Practical Implementation: See how to structure domain, usecase, and adapter layers in a real Kotlin Spring Boot project.
   • Dependency Inversion: Learn how ports (interfaces in the domain) define contracts, and adapters provide concrete implementations.
   • Testability: Appreciate how this architecture facilitates easier unit and integration testing.
2. Develop with Kotlin & Spring Boot:
   • Modern Kotlin: Leverage Kotlin's conciseness, null safety, and functional features for backend development.
   • Spring Boot Best Practices: Set up Spring Boot applications, manage dependencies, and configure core components.
   • RESTful API Design: Implement CRUD (Create, Read, Update, Delete) APIs with Spring Web.
3. Integrate Kafka for Event-Driven Communication:
   • Producer Implementation: Learn to publish events (e.g., ProductCreatedEvent) to a Kafka topic from a Spring Boot service.
   • Asynchronous Processing: Understand the basics of decoupling services using an event bus.
   • Configuration: Set up Kafka producers within a Spring Boot context.
4. Utilize Jooq for Type-Safe Database Interaction:
   • Jooq Code Generation: Learn to generate Jooq classes from your PostgreSQL schema.
   • Fluent SQL Building: Write type-safe, readable, and maintainable SQL queries in Kotlin.
   • Repository Pattern: Implement data access layers using Jooq within the hexagonal architecture.
   • Database Migrations with Flyway: Manage database schema evolution effectively.
5. Build and Manage Microservices:
   • Service Decomposition: Understand how to break down a larger system into smaller, independent services (Product and Category).
   • Inter-Service Communication: Implement synchronous API calls between services (Product service calling Category service).
   • Configuration Management: Handle service-specific configurations (ports, database connections, Kafka brokers).
6. Containerize with Docker & Docker Compose:
   • Environment Setup: Easily spin up a complete development environment (PostgreSQL, Zookeeper, Kafka) using Docker Compose.
   • Service Orchestration: Understand how Docker Compose manages multiple containers.
7. Practical CRUD Operations:
   • Implement the fundamental building blocks of most applications for both Product and Category entities.
8. Understand Project Structure & Modularity:
   • Learn to organize code effectively in a microservice project, promoting clarity and maintainability.

Technical Stack & Highlights:

• Languages & Frameworks: Kotlin, Spring Boot 3+
• Architecture: Hexagonal (Ports and Adapters)
• Database: PostgreSQL
• Database Access: Jooq (with Flyway for migrations)
• Messaging: Apache Kafka
• API: RESTful APIs (Spring Web)
• Build Tool: Gradle (Kotlin DSL)
• Containerization: Docker, Docker Compose
• Key Features:
  • Two independent microservices: product-backend & category-backend.
  • Full CRUD operations for Products and Categories.
  • Synchronous API call from Product service to Category service (e.g., to validate category existence).
  • Asynchronous event publishing to Kafka when a product is created.
  • Clear separation of concerns following Hexagonal principles.
  • Ready-to-run Docker Compose setup for all infrastructure.

Prerequisites:

• Basic understanding of Kotlin (or Java, with a willingness to learn Kotlin syntax).
• Familiarity with Spring Boot fundamentals.
• Basic knowledge of REST APIs.
• Docker and Docker Compose installed.
• JDK 17 or higher.

Why This Project is a Great Learning Investment:

• Practical, Not Just Theoretical: Go beyond blog posts and tutorials with a working, multi-component system.
• Modern & Relevant Stack: Learn technologies highly in demand in the industry.
• Clean Architecture: Understand principles that lead to maintainable and scalable software.
• Save Time: Skip the boilerplate and dive straight into learning core concepts with a well-structured foundation.
• Extendable: Use this as a base to add more features, implement consumer logic for Kafka, add security, or explore other patterns.