How does a three-tier architecture improve application reliability during failures?

A three-tier architecture enhances application reliability during failures by allowing only the specific portion of the application that fails to be unavailable. In this design, the application is divided into three distinct layers: the presentation layer (user interface), the application layer (business logic), and the data layer (database). Each layer functions independently, so if one layer encounters an issue, it doesn't necessarily impact the others.

For instance, if there is a failure in the application layer (where the business logic occurs), users can still access the presentation layer and, to some extent, the data layer may remain operational. This isolation means that the overall system can continue to serve its purpose, maintaining a level of accessibility and functionality, while issues are resolved within the affected layer.

The other options present scenarios that would not contribute to reliability during failures, as they suggest broader impacts that could hinder the entire application's availability, which runs counter to the intended benefits of a three-tier architecture.