Used for applications that can be organized into a hierarchy of layers. Each layer provides services to the layer above and uses services from the layer below.
Components
- Layers: Each layer groups components at an abstraction level (domain, data, infra, etc)
- There is dependancy between layers
- Connectors are method (or RPC) calls across layer boundaries behind interfaces
- Communication happens between adjacent layers
Pros and Cons
Pros:
- Since each layer is decoupled, it is possible to swap implementations within a layer if the contracts are kept.
- The system is easy to understand due to abstraction Cons:
- Abstractions can add overhead, and performance requirements could force coupling
- Not all systems map cleanly to these structures
Variants
Allowing non-adjacent layer communication
- This just allows a higher layer to call a lower layer directly but things like this tend to erode boundaries. An important example here is the architecture of UDP