Short note: Design patterns in deployment

(Interpreted as the effect of using design patterns when the system is implemented and deployed.)

Design patterns are proven solutions to recurring design problems. Their use has these effects on development and deployment:

1. Better structure and quality. Patterns such as Facade, Layers and Factory give a clean architecture; the system is loosely coupled, so components can be installed, replaced or upgraded independently.
2. Easier distribution and deployment. Patterns like Proxy, Broker, Facade and Data Access Object separate the client from the server or database, so tiers (presentation, business, data) can be deployed on different nodes with little change in code.
3. Flexibility and configuration. Strategy, Factory and Abstract Factory allow behaviour or the database/driver to be chosen by configuration at deployment time without recompiling.
4. Scalability and performance. Singleton, Flyweight, Object Pool and Cache reduce resource use; Observer/Publisher-Subscriber supports distributed updates.
5. Maintenance and communication. Because patterns are well-known, deployed systems are easier to understand, test and maintain; documentation uses a shared vocabulary.
6. Possible costs. Misuse adds extra classes, indirection and a performance overhead, and increases complexity for small systems.

 Client --> [Proxy/Facade] --> [Business tier] --> [DAO] --> DB
   (node 1)       (node 2)          (node 3)       (node 4)