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7.1.3.1: Selecting a topology

7.1.3.1: Selecting a topology

A variety of factors typically are considered when you are deciding on the best topology for deploying a WebSphere application. The major factors for picking a topology include:

  • Security. Some security concerns can be addressed by physically separating the Web server from the application server by using firewalls.
  • Performance. To maximize performance, the response time for transactions needs to be as short as possible. Two topologies can be used to improve transaction performance:
  • Throughput. To process as many transactions as possible within a given time period, application server clones can be created to increase the number of concurrent transactions that the application can perform. These application server clones can be added through vertical or horizontal scaling.
  • Availability. To avoid a single point of failure and maximize the system's availability, the topology must have some degree of process redundancy. High-availability topologies typically involve horizontal scaling across multiple machines. (Vertical scaling can improve availability by creating multiple processes, but the machine itself becomes a point of failure.) A Network Dispatcher server can direct client HTTP requests to the available Web servers, bypassing any that are offline; it can also be backed up by another server to eliminate it as a single point of failure. Workload management of application servers and administrative servers also improves availability and failover support.
  • Maintainability. The system's topology affects the ease with which its hardware and software can be updated. For instance, using multiple WebSphere domains or horizontal scaling can make a system easier to maintain because individual machines can be taken offline for hardware and software upgrades without interrupting the application. However, sometimes maintainability conflicts with other topology considerations. For example, limiting the number of application server instances makes the application easier to maintain but can have a negative effect on its throughput, availability, and performance.
  • Maintaining session state between client HTTP requests. This does not apply if your application runs on a single application server instance or is completely stateless. However, session state is an important consideration for stateful applications and applications that run on multiple machines or application server instances. A session can be shared between multiple application server processes (clones) by saving the session state to a database. In addition, the configuration of an HTTP redirector such as Network Dispatcher affects how the session state is maintained.

Inform.gif (183 bytes) Whichever topology you decide on, a best practice is to partition your testing and production acceptance environments in exactly the same way as your production environment. This helps you recognize and address problems with your application before it is actually deployed.

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