WebSphere Application Server V7.0: Concepts ... - IBM Redbooks

7.2.1 Scaling overview
Note: In order to be scalable you need a scalable application. If an application
is not designed to be scalable, the scalability options are limited.
Consider additional hardware resources as a step for improving system
performance. There are two ways to improve performance when adding
hardware:
► Vertical scaling
Vertical scaling means increasing the throughput by adding resources inside
the server and operating system image to handle more requests in parallel.
From a hardware perspective, we can, for example, increase the number of
processors for a server. By upgrading the system hardware with additional
processors, the server can potentially gain a higher throughput. This concept
is relatively easy to implement and can apply to any server in an environment.
Examine vertical scaling at every potential bottleneck in your architecture.
► Horizontal scaling
Horizontal scaling means adding additional separated resources to handle
additional load. This applies to multi-tier scenarios and can require the use of
additional components like a load balancer that sits in front of the duplicated
servers and makes them appear as a single instance.
Note: Adding resources usually affects the dynamics of the system and
can potentially shift the bottleneck from one resource to another. Therefore
it is important to have a balanced system.
In a single tier scenario, the Web application and database servers are all
running on the same system. Creating a cluster and spreading application
servers across systems should improve the throughput. But at the same time,
additional systems introduce new communication traffic and load to the database
server. Ask yourself the following questions:
► How much network bandwidth will this server configuration consume?
► What will the performance improvement by adding more systems be?
Because of these questions, we recommend that you always perform a
scalability test to identify how well the site is performing after a hardware change.
Throughput and response time can be measured to ensure that the result meets
your expectations.
232 WebSphere Application Server V7.0: Concepts, Planning, and Design