Kerrosarkkitehtuuri

Kerrosarkkitehtuuri, known in English as layered architecture, is a software architecture pattern in which components are organized into discrete layers arranged in a hierarchical order. Each layer provides services to the layer above it and relies only on the abstraction of the layer below, enabling modular separation of concerns. The pattern is widely used in enterprise application design, operating systems, middleware, and larger distribution systems like Internet of Things deployments.

Typical layers include a user interface layer, a business logic or application layer, a domain or service layer, a data access layer, and a persistent storage or database layer. However, the exact number of layers and their responsibilities can vary according to the domain and the desired level of abstraction. In many cases, the pattern is expressed with a horizontal slicing of responsibilities into tiers: presentation, domain, infrastructure. The most common justification for using kerrosarkkitehtuuri is the reduction of coupling between components, making systems easier to test, evolve, and replace parts without affecting others.

The main strengths of the model are clear separation of concerns, facilitate understanding of system structure, improved testability, and the ability to replace implementations within a layer. Weaknesses include potential performance overhead due to added indirection, risk of over‑engineering and excessive layering, and challenges in maintaining strict boundaries if mature best‑practice guidelines are not followed.

Kerrosarkkitehtuuri is often contrasted with other styles such as monolithic, microkernel, microservices, and event‑driven architectures. Its adoption is typically determined by organizational standards, legacy integration needs, or performance constraints that require well‑defined interfaces and encapsulation. In practice, successful implementations of kerrosarkkitehtuuri rely on consistent naming conventions, thorough documentation of layer interfaces, and disciplined adherence to well‑defined architectural contracts.