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
Scalability
Scalability the ability to support the required quality of service requirement as the load on the system increases
There are two types of scaling: horizontal and vertical scaling.
Vertical scaling increases the capacity of the system, but can have a negative impact on reliability
and availability, as the impact of the single point of failure increases.
Horizontal scaling increases the reliability, availability
and performance of the system, but it also increases the complexity.
This has a negative impact on the manageability of the system.
Effects
1 tier:
Very Limited
2 tier:
Hard
n tier:
Good. Horizontal and vertical scaling can both be achieved. (Resource pooling, adding hardware, etc.)
J2EE:
J2EE supports vertical scaling by means of automatic lifecycle management. Increased capacity means that the server can manage more components.J2EE supports horizontal scaling by means of clustering and load-balancing.
Vertical scaling
Vertical scaling is achieved by adding more capacity (such as disks, memory, CPUs) to existing servers.
It requires few to no changes to the existing architecture, so it is easily achieved. Vertical scaling is usually cheaper than horizontal scaling.
Horizontal scaling
Horizontal scaling is achieved by adding more servers to the existing system.
It has a high impact on the architecture of a system, so it is not easiliy achieved.