architecture-patterns

# 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 mechanism...