Hexagonal architecture example with Python

Example of a microservice designed following the definition of hexagonal architecture. Depending on the size of our system, there may be more sub-layers within the application, domain or infrastructure. So it is requested to take it as a base.

Let's explain architecture

• Principal layers:
  • Domain
  • Application
  • Infrastructure
  • Test

Domain:

• In this layer we place all the business logic, such as:
  • Entities with business rules.
  • Interfaces or ports that define the behavior of use cases, repositories or events that are then implemented by the application and infrastructure layers.
  • It is important to highlight that in this layer we should not use 3rd party technologies

Application:

• In this layer we put all the functionality that is related to our application, for example:
  • Services which implement the use cases defined in the domain layer
  • Data validations that allow verifying if the input data is correct, such as character lengths.

Infrastructure:

• In this layer we place the input and output adapters, which implement the interfaces defined for the repositories or business events. For example:
  • Repository that stores the data in a database.
  • Events that communicate with some queuing engine.
  • Handlers that serve as the entry point and that call the application services.
  • In this layer we can implement any 3rd party library.

Test:

• In this directory we will place all the tests of our application.

• Structure

├── app
│   ├── application 
│   │   ├── validators # Validation logic for input data
│   │   └── services # Implement the use cases
│   ├── domain
│   │   ├── entities # Entities with business logic
│   │   ├── events # Interface that defines how an event behaves
│   │   ├── repositories # Interface that defines how a data repository behaves
│   │   ├── use cases # Interface that defines the use cases of the application
│   │   └── exceptions # Domain exceptions
│   ├── infrastructure
│   │   ├── events # Implements the domain event interface
│   │   ├── handlers # Application entry point
│   │   ├── repositories # Implements the domain repository interface
│   │   ├── schemas # Data structures used as input and output
│   │   └── container # Dependency injector
└───└── test

Technologies

• python
• fastapi
• dependency-injector
• pytest
• pydantic
• docker
• make

Commands

$ make build #Create docker images

$ make up #Run the docker container

$ make down #Stop the docker container

References

• https://alistair.cockburn.us/hexagonal-architecture/
• http://wiki.c2.com/?HexagonalArchitecture