The hexagonal architecture, or ports and adapters architecture, is an architectural pattern used in software design. It aims at creating loosely coupled application components that can be easily connected to their software environment by means of ports and adapters. This makes components exchangeable at any level and facilitates test automation.
Each component is connected to the others through a number of exposed “ports”. Communication through these ports follow a given protocol depending on their purpose. Ports and protocols define an abstract API that can be implemented by any suitable technical means (e.g. method invocation in an object-oriented language, remote procedure calls, or Web services).
The granularity of the ports and their number is not constrained:
- A single port could in some case be sufficient (e.g. in the case of a simple service consumer);
- Typically, there are ports for event sources (user interface, automatic feeding), notifications (outgoing notifications), database (in order to interface the component with any suitable DBMS), and administration (for controlling the component);
- In an extreme case, there could be a different port for every use case, if needed.
Adapters are the glue between components and the outside world. They tailor the exchanges between the external world and the ports that represent the requirements of the inside of the application component.