FastAPIVới app nhỏ, layer đơn giản như routers/services/repositories đủ dùng. Với app lớn, nên tổ chức theo feature/domain để giảm coupling: mỗi domain có router, schemas, service, repository và tests riêng.
Quan trọng là route handler mỏng: parse request, gọi service/use-case, trả response. Business logic không nên nằm dày trong handler vì khó test và khó reuse cho worker/message consumer.
For small apps, simple layers such as routers/services/repositories are enough. For large apps, organize by feature/domain to reduce coupling: each domain owns its router, schemas, service, repository and tests.
The route handler should stay thin: parse request, call a service/use-case and return a response. Business logic should not be dense inside handlers because it becomes hard to test and reuse from workers/message consumers.