Architecture Patterns

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

Given: a service boundary or module to architect. Produces: layered structure with clear dependency rules, interface definitions, and test boundaries.

When to Use This Skill

• Designing new backend services or microservices from scratch
• Refactoring monolithic applications where business logic is entangled with ORM models or HTTP concerns
• Establishing bounded contexts before splitting a system into services
• Debugging dependency cycles where infrastructure code bleeds into the domain layer
• Creating testable codebases where use-case tests do not require a running database
• Implementing domain-driven design tactical patterns (aggregates, value objects, domain events)

Core Concepts

1. Clean Architecture (Uncle Bob)

Layers (dependency flows inward):

• Entities: Core business models, no framework imports
• Use Cases: Application business rules, orchestrate entities
• Interface Adapters: Controllers, presenters, gateways, translate between use cases and external formats
• Frameworks & Drivers: UI, database, external services, all at the outermost ring

Key Principles:

• Dependencies point inward only; inner layers know nothing about outer layers
• Business logic is independent of frameworks, databases, and delivery mechanisms
• Every layer boundary is crossed via an abstract interface
• Testable without UI, database, or external services

2. Hexagonal Architecture (Ports and Adapters)

Components:

• Domain Core: Business logic lives here, framework-free
• Ports: Abstract interfaces that define how the core interacts with the outside world (driving and driven)
• Adapters: Concrete implementations of ports (PostgreSQL adapter, Stripe adapter, REST adapter)

Benefits: