.NET Core Architecture

House architecture conventions for .NET 8 backend services. This covers how a service is structured; for language-level conventions see the csharp skill.

Layering

Dependencies point inward only. Domain knows nothing about anything else, and Infrastructure is the one layer allowed to reference a database or an SDK — which is what lets the inner layers be tested without either.

Domain          entities, value objects, domain events, interfaces  → no dependencies
Application     use cases, CQRS handlers, DTOs, validators          → Domain
Infrastructure  EF Core, external APIs, implementations of Domain interfaces → Domain + Application
Api             endpoints, DI wiring, middleware                    → all of the above

The test that keeps this honest: if Domain compiles with no package references beyond the BCL, the boundary is intact.

Entities enforce their own invariants: private setters, a private parameterless constructor for EF Core's materialiser, and a static factory that validates. Public setters mean any layer can put the entity into an invalid state, and then "the domain guarantees X" is just a comment.