Hexagonal Architecture

A way to isolate business logic in code

Table of contents

• History
• Purpose
• Principles
• The separation of concerns
• Three Layers
• Inner layer isolation — dealing with dependencies
• Ports and Adapters
• Domain in isolation
• Direction of flow
• Ease of testing
• Sample with Spring and Kotlin
• Hexagonal vs Onion vs Clean
• Conclusion
• Reference

A bit of history

Published in a blog by Alistair Cockburn in 2005

The hexagonal architecture is synonym to “ports and adapters pattern”, but nowadays “hexagonal architecture” is better known. Moreover, it is a step further than the four (4) layered architecture that allows to separate the layers per responsibility. The hexagonal architecture on the other hand clearly suggests a focus on the domain isolation.

The term “hexagonal” comes from the graphical conventions that shows the application component like a hexagonal cell. The six borders represents the multiple interfaces that the component may expose to the external world.