software-architecture

SOLID principles—Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, and Dependency Inversion—create modular, flexible code by isolating concerns and managing dependencies. Each principle targets a specific design problem: SRP keeps classes focused, Open/Closed allows extension without modification, Liskov ensures substitutable subtypes, Interface Segregation prevents fat interfaces, and Dependency Inversion decouples high-level from low-level modules. Applying them incrementally reduces technical debt and improves maintainability.

Clean Architecture organizes code into four concentric layers—Domain (business logic), Application (use cases), Interface Adapters (controllers, presenters), and Frameworks (databases, web servers)—ensuring dependencies point inward only. This layering isolates domain logic from external concerns, making systems testable, scalable, and resilient to framework changes. Structure your TypeScript project with each layer in separate directories, inject dependencies downward, and keep business rules independent of delivery mechanisms.

Design patterns solve recurring structural problems. Repository abstracts data access, allowing you to swap persistence layers without changing business logic. Factory centralizes object creation, reducing coupling to concrete classes. Strategy encapsulates interchangeable algorithms, letting you select behavior at runtime. Use them when you encounter repeated patterns—avoid premature abstraction. Choose based on the specific coupling or complexity they resolve in your codebase.

Architecture Decision Records (ADRs) capture significant design choices—the context, decision, and consequences—creating a searchable history. Document decisions when choosing between patterns, technology trade-offs, or structural changes. Store ADRs as markdown files in your repository; reference them during code review and onboarding. ADRs prevent repeated debates, clarify rationale for future maintainers, and reduce technical debt by making reasoning explicit.

Yes. Refactor incrementally by identifying responsibilities, extracting domain logic into separate modules, and inverting dependencies. Start with one layer or one principle—separate a god class following SRP, introduce interfaces to decouple modules, reorganize folders to reflect layers. This gradual approach prevents breaking changes and lets your team adopt patterns progressively while delivering value.

Architectural patterns (Clean Architecture, layered, microservices) organize entire systems and define how major components interact and communicate. Design patterns (Factory, Strategy, Observer) solve localized problems within code—object creation, algorithm selection, or event handling. Architectural patterns set system structure; design patterns implement that structure. Both enforce separation of concerns, but at different scales.