Hexagonal Architecture
Hexagonal Architecture, also known as Ports and Adapters, it is used in software design to create a clear separation between the core logic of an application and its external dependencies (input/output mechanisms). The business logic doesn't depend in any way on the external dependencies (where any dependency can be easily replaced without affecting the core/domain logic).
Avoid hexagonal architecture when the application is small or simple, as it can add unnecessary complexity.
Key Concepts
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Ports: Interfaces that define how the application interacts with the outside world. They are abstractions that allow the core logic to communicate with external systems.
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Adapters: Implementations of the ports that connect the core logic to external systems. They translate the data and calls between the domain entities and the external systems. It is the application layer, explaining how the pieces fit together and how the flow is orchestrated.
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Domain Layer: Focus on the what, it is the central part of the application that contains the business entities, rules and logic. It is independent of any external systems or frameworks and focuses on the application's functionality.
In a nutshell, hexagonal architecture is designed by layers. The application layer from the request coming (Driving adapter), goes to the domain layer, and keep going through other infrastructure layer to the final destination (Driven adapter). This division into layers gives the flexibility to make changes on the adapters easily. For example, you can swap out Oracle by SQL Server (or Mongo), or enable easily an additional entry point for a new consumer.
Technical aspects belongs to the application layer (adapters), while business logic belongs to the domain layer. This way, the domain layer is not affected by changes in the external systems. Rule of thumb: if you swap an external system for a different one, and the core logic is affected, then the architecture is not hexagonal.
Benefits
- Separation of Concerns: The core logic is isolated from external systems, making it easier to maintain and test.
- Testability: The core logic can be tested independently of external systems, allowing for easier unit testing and mocking of dependencies.
- Developers can work independently on different adapters without affecting the core logic.
- Flexibility: External systems can be changed or replaced without affecting the core logic. Each adapter gather all code related to a specific external system, allowing developers to optimize the performance of each adapter independently.
- Stability: The core logic remains stable even as external systems evolve or change, reducing the risk of introducing bugs or breaking changes. It is important to avoid tight coupling between the core logic and external systems so breaking changes are minimized.