Which pattern can enhance performance by caching frequently accessed configuration settings from an external system?

The pattern that enhances performance by caching frequently accessed configuration settings from an external system is the Proxy or Decorator pattern. This pattern acts as an intermediary for another object to control access to it, allowing for functionalities such as lazy loading, access control, and caching.

By implementing caching through a Proxy, the application can store frequently accessed configuration settings in memory after retrieving them from the external system. This reduces the number of calls made to the external system, thereby minimizing latency and improving response times. When subsequent requests for the same configuration settings are made, the Proxy can serve the cached version instead of fetching it again from the external source, leading to more efficient use of resources and better overall performance.

Additionally, the Proxy pattern allows for flexibility in managing how and when data is retrieved and cached, providing opportunities for additional enhancements like updating configurations or refreshing cached data when necessary without disrupting the underlying system.

The other patterns listed do not focus specifically on the concept of caching configurations. The Observer pattern is more about establishing a subscription-based model to notify changes, the Factory pattern focuses on object creation, and the Strategy pattern involves selecting an algorithm at runtime, none of which directly deal with caching configuration settings for performance enhancement.