Layered / N-tier

Layered architecture groups code by responsibility. A common direction is presentation → application → domain, with infrastructure serving outer layers. Use it when the responsibilities are stable and a feature-oriented structure would not be clearer.

src/app/
├── presentation/
├── application/
├── domain/
└── infrastructure/

Complete Configuration

deply:
  paths: ["."]
  exclude_files:
    - '.*/\.venv/.*'
    - '.*/tests?/.*'
    - '.*/migrations/.*'
  layers:
    - name: presentation
      collectors:
        - type: directory
          directories: ["src/app/presentation"]
    - name: application
      collectors:
        - type: directory
          directories: ["src/app/application"]
    - name: domain
      collectors:
        - type: directory
          directories: ["src/app/domain"]
    - name: infrastructure
      collectors:
        - type: directory
          directories: ["src/app/infrastructure"]
  ruleset:
    domain:
      disallow_layer_dependencies: [presentation, application, infrastructure]
      disallow_external_imports: [django, fastapi, flask, sqlalchemy, requests]
    application:
      disallow_layer_dependencies: [presentation, infrastructure]
    infrastructure:
      disallow_layer_dependencies: [presentation]

This enforces inward source dependencies. It does not require every request to pass through every layer. If application code intentionally uses concrete infrastructure, remove that one restriction rather than introducing empty interfaces.

Validate

deply validate --config=deply.yaml
deply analyze --parallel --config=deply.yaml

Reference: Patterns of Enterprise Application Architecture.