Objective 2.1: Recognize the effect on each of the following characteristics of two tier, three tier and multi-tier architectures: scalability, maintainability, reliability, availability, extensibility, performance, manageability, and security
Objective 2.2: Recognize the effect of each of the following characteristics on J2EE technology: scalability, maintainability, reliability, availability, extensibility, performance, manageability, and security
Reliability
Reliability is the ability to ensure the integrity and consistency of the application and all of its transactions
This means that when the load on the system increases, the system should still process all requests accurately.
Reliability is achieved by applying horizontal scalability.
Increased reliability has a positive impact on availability.
Effects
1 tier:
Single point of failure but data consistency is fairly reliable.
2 tier:
Poor. Single point of failure, usually the database.
n tier:
Good when using fault tolerance and horizontal scaling.
J2EE:
J2EE facilitates reliability requirements through support for clustering and load-balancing.