The layers architecture is often confused with the N-Tier architecture, and vice versa. Despite the similarities between the two patterns, layers and tiers are conceptually different: a layer is a logical boundary, whereas a tier is a physical boundary. All layers in the layered architecture are bound by the same lifecycle: they are implemented, evolved, and deployed as one single unit. On the other hand, a tier is an independ‐ ently deployable service, server, or system. For example, consider the N-Tier system in Figure 8-7.

Figure 8-7. N-Tier system

The system depicts the integration between physical services involved in a web-based system. The consumer uses a browser, which can run on a desktop computer or a mobile device. The browser interacts with a reverse proxy that forwards the requests to the actual web application. The web application runs on a web server and commu‐ nicates with a database server. All of these components may run on the same physical server, such as containers, or be distributed among multiple servers. However, since each component can be deployed and managed independent of the rest, these are tiers and not layers.

Layers, on the other hand, are logical boundaries inside the web application.