Answer.

Clean Architecture is an approach to designing complex software systems that ensures the independence of business logic from frameworks, databases, user interfaces, and other external factors. It is based on the separation of code into layers, which allows for minimal mutual influence.

In classic Clean Architecture, we see inner layers (Use Cases, Entities) and outer layers (Frameworks, Gateways, Controllers). Dependency inversion occurs only inwards, allowing easy configuration, modification, and testing of systems without the risk of disrupting critical business logic.

Example code (in Python):

# Entity
class Order:
    def __init__(self, id, total):
        self.id = id
        self.total = total

# Use Case
class CompleteOrderUseCase:
    def __init__(self, order_repository):
        self.order_repository = order_repository
    def execute(self, order_id):
        order = self.order_repository.get_by_id(order_id)
        order.completed = True
        self.order_repository.save(order)

Key features:

• Independence of business logic from infrastructure and user interface
• Ability to make easy changes and testing due to weak coupling of layers
• Ensuring extensibility and support for automation strategies

Trick questions.

Can all layers of Clean Architecture be implemented as separate services?

Not necessarily. Sometimes separating each layer into its own service is impractical due to high coupling or overhead from communication. Layers represent logical separation; physical isolation is only necessary when justified.

Can the direction of dependencies rule in Clean Architecture be violated if it speeds up development?

No, as even a short-term time savings leads to increased complexity in future maintenance. The direction of dependencies is a core principle of Clean Architecture, and violating it results in losing the structure's advantages.

Must business rules always be implemented exclusively at the inner layer?

Yes, all important business rules should reside in the inner layer (Entities or Use Cases) so that changes in external dependencies do not affect business logic.