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7.1: Using WebSphere Application Server in a multimachine environment
7.1: Using WebSphere Application Server in a multimachine environment
The basic single machine WebSphere configuration can be extended by distributing the
application over multiple machines and by making more efficient use of the processing
power of each machine in the configuration. Some of the reasons for creating WebSphere
Application Server applications that run on multimachine systems include:
- Scalability. Increasing processing power by adding more machines
enables the system to handle a higher client load than that provided by the basic,
single-machine configuration. Ideally, it is possible to handle any given load by adding
more servers and machines. Each additional machine must process its fair share of client
requests. (That is, a share of the total system load that is proportional to its
processing power.)
- Security. Multimachine configurations can use firewalls to protect
sensitive resources from unauthorized access.
- Shared data access. Placing back-end resources such as databases on
different machines can enable these resources to be shared more easily.
- Availability and failover support. In a single-machine configuration,
any failure means that the entire system is unavailable. However, in multimachine
configurations, the system continues to operate if any one machine or server in the system
fails for any reason. Failover support distributes client requests to the remaining
servers, which ensures continued client access without significant interruptions. (In
practice, failover is not entirely transparent to clients.)
- Fault isolation. Configurations that provide simple failover support
are concerned only with individual server failures that have no effect on the performance
of other servers. However, in some situations a malfunctioning server can create problems
for other servers that are otherwise functioning normally. For example, it can consume
more than its share of system and database resources, preventing other servers from
gaining adequate access to these resources. A configuration that provides more robust
failover support includes a degree of fault isolation, reducing the potential for the
failure of one server to affect other servers. WebSphere Application Server can be
configured to provide fault isolation between different parts of a system.
- Dynamic changes to configurations. Administrators can modify the
system's configuration without interrupting its operation. For instance, they can add or
remove clones of servers to handle variations in the client load, change server
characteristics and propagate the changes to its clones, temporarily stop servers for
maintenance, and so forth. This enhances the manageability and flexibility of the system.
- Mixed application server configurations. Some multimachine
configurations allow multiple versions of an application server to be deployed
simultaneously. Applications can be deployed in stages and the system's hardware and
software can be easily upgraded. When combined with the ability to make dynamic changes to
the configuration, a mixed server configuration can be used to upgrade an application
without any interruption of service.
Note: The ability to run different versions of an application server in a
configuration applies only if the application servers are running under the same version
of the application code. You cannot run application servers under different versions of
WebSphere Application Server in the same administrative domain.
This section describes how you can achieve these goals in multimachine configurations.
It is an overview of the various ways that you can use to scale up the basic,
single-machine WebSphere system to meet the needs of your organization, and is not
intended to be an exhaustive discussion of WebSphere configurations.
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