architecture-patterns

Implement proven backend architecture patterns for maintainable, testable, and scalable systems. 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. Layers (dependency flows inward): Key Principles: Components: Benefits: Strategic Patterns: Tactical Patterns: Dependency rule in one sentence: every import statement in domain/ and use_cases/ must point only toward domain/ ; nothing in those layers may import from adapters/ or infrastructure/ . The hallmark of correctly applied Clean Architecture is that every use case can be exercised in a plain unit test with no real database, no Docker, and no network: Business logic has leaked into the infrastructure layer. Move all database calls behind an IRepository interface and inject an in-memory implementation in tests (see Testing section above). The use case constructor must accept the abstract port, not the concrete class.