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

Note: IBM HTTP Server for z/OS offers the unique feature of a scalable mode.
This allows the server to start additional instances of itself to offer vertical
scalability if the performance goals are not met.
DMZ secure server
The DMZ secure proxy provides horizontal and vertical scaling capabilities
besides the scaling activities on a per server basis. When scaling vertically, make
sure that you have sufficient resources. Also, be aware that this provides only
limited high availability. In any scaling scenario you need an IP sprayer like the
Edge Components to spread the incoming traffic across all proxy servers.
WebSphere containers
Scaling at the application server layer can be done with vertical or horizontal
scaling, or both. Vertical scaling at the application server layer can be done
physically or logically. WebSphere Application Server is a Java application itself
and can take advantage of additional processors or memory in the machine.
WebSphere Application Server applications can be clustered vertically, providing
multiple copies of the same application on the same physical machine.
WebSphere Application Server also supports horizontal cloning of applications
across multiple machines, which do not need to be identical in terms of physical
resources.
Default messaging
With the messaging engine and the service integration bus, WebSphere offers
the ability to scale messaging resources more efficiently. Using a cluster as a
service integration bus member, you can create partitioned destinations. This
enables a single logical queue to spread across multiple messaging engines. In
this scenario, all messaging engines are active all the time. For n cluster
members, the theory is that each receives an nth of the messages. This allows
for greater scalability of messaging resources across the cell. One key factor to
consider in this design is that message order is not preserved. That may or may
not be significant, depending on the nature of the application.
Multiple messaging engines for a cluster bus member is not the default setting.
For workload management, you must take steps to add additional messaging
engines. To make sure that the messaging engines are really running on different
servers you must configure proper high availability policies. WebSphere
Application Server V7 features a wizard for high availability policy setup which
can be used for most topologies.
234 WebSphere Application Server V7.0: Concepts, Planning, and Design