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Architecture Patterns

Master proven backend architecture patterns including Clean Architecture, Hexagonal Architecture, and Domain-Driven Design to build maintainable, testable, and scalable systems.

When to Use This Skill

• Designing new backend systems from scratch
• Refactoring monolithic applications for better maintainability
• Establishing architecture standards for your team
• Migrating from tightly coupled to loosely coupled architectures
• Implementing domain-driven design principles
• Creating testable and mockable codebases
• Planning microservices decomposition

Core Concepts

1. Clean Architecture (Uncle Bob)

Layers (dependency flows inward):

• Entities: Core business models
• Use Cases: Application business rules
• Interface Adapters: Controllers, presenters, gateways
• Frameworks & Drivers: UI, database, external services

Key Principles:

• Dependencies point inward
• Inner layers know nothing about outer layers
• Business logic independent of frameworks
• Testable without UI, database, or external services

2. Hexagonal Architecture (Ports and Adapters)

Components:

• Domain Core: Business logic
• Ports: Interfaces defining interactions
• Adapters: Implementations of ports (database, REST, message queue)

Benefits:

• Swap implementations easily (mock for testing)
• Technology-agnostic core
• Clear separation of concerns

3. Domain-Driven Design (DDD)

Strategic Patterns:

• Bounded Contexts: Separate models for different domains
• Context Mapping: How contexts relate
• Ubiquitous Language: Shared terminology

Tactical Patterns:

• Entities: Objects with identity
• Value Objects: Immutable objects defined by attributes
• Aggregates: Consistency boundaries
• Repositories: Data access abstraction
• Domain Events: Things that happened

Clean Architecture Pattern

Directory Structure

app/
├── domain/           # Entities & business rules
│   ├── entities/
│   │   ├── user.py
│   │   └── order.py
│   ├── value_objects/
│   │   ├── email.py
│   │   └── money.py
│   └── interfaces/   # Abstract interfaces
│       ├── user_repository.py
│       └── payment_gateway.py
├── use_cases/        # Application business rules
│   ├── create_user.py
│   ├── process_order.py
│   └── send_notification.py
├── adapters/         # Interface implementations
│   ├── repositories/
│   │   ├── postgres_user_repository.py
│   │   └── redis_cache_repository.py
│   ├── controllers/
│   │   └── user_controller.py
│   └── gateways/
│       ├── stripe_payment_gateway.py
│       └── sendgrid_email_gateway.py
└── infrastructure/   # Framework & external concerns
    ├── database.py
    ├── config.py
    └── logging.py