Onion Architecture

Onion Architecture is a software design pattern that organizes an application into concentric layers, with the core domain logic at the center and dependencies pointing inward. It emphasizes separation of concerns, testability, and maintainability by decoupling the business logic from external concerns like databases, user interfaces, or frameworks. This architecture is often used in domain-driven design (DDD) to create clean, scalable applications.

Also known as: Onion Pattern, Clean Architecture, Hexagonal Architecture variant, Ports and Adapters, Layered Architecture with Dependency Inversion

Why learn Onion Architecture?

Developers should use Onion Architecture when building complex, enterprise-level applications where business logic needs to be isolated from infrastructure details, such as in microservices or long-lived systems. It is particularly beneficial for improving testability, as the core domain can be tested without external dependencies, and for facilitating changes to external components without affecting the business rules. This makes it ideal for projects requiring high maintainability and adherence to SOLID principles.

Learning Resources

• docs: Onion Architecture: Part 1 - Introduction
• tutorial: Implementing Onion Architecture in ASP.NET Core
• video: Onion Architecture Explained - YouTube
• book: Clean Architecture by Robert C. Martin