A Comprehensive Guide to IBM WebSphere Host Publisher Version 3.5

594 IBM WebSphere Host Publisher Version 3.5

19.1 Cloning

Cloning is a mechanism provided by the WebSphere Application Server (WAS)

administration system that allows for the creation of multiple copies of an object

such as an application server. Cloning is the process of taking a server that you

have set up and creating a model based upon that setup. Once you have a

model, you can create clones of that server.

With extra clones running, you can improve the performance of your server.

However, you should keep in mind that there is a point of diminishing returns,

where the clones that you add will actually slow you down because of the extra

maintenance and traffic they generate and their management.

In brief, the system administrator creates a model for an application server, and

from this model may create any number of copies or clones. The model is a

logical representation of the application server that exists only as information

managed by the WAS administration system. It has the same structure and

attributes as a real application server: it may contain servlet engines, EJB

containers, servlets, EJBs, and so on, and allows the administrator to view and

modify any properties of these logical objects. However, it is not associated with

any node, nor does it correspond to any real server process running on any

node. The clones created from this model, on the other hand, represent real

application server processes running on real nodes. They are identical in every

way to the model from which they were created, except for some clone-specific

attributes which must be set on a per-clone basis. Furthermore, if the system

administrator makes changes to the model, these changes will be automatically

reflected to all the clones.

Note: Several clones from the same model may be instantiated on multiple

nodes, and it is also possible to instantiate multiple clones on the same node.

WebSphere Application Server (WAS) Version 3.5 Advanced Edition supports

multiple JVMs (application servers). These JVMs can be clones of each other

containing the same EJBs and the same Web applications by processing the

same URL. These clones can be on the same machine or can be distributed

across different machines. In WAS, when the clones are on the same machine,

we refer to

vertical cloning and when the clones are distributed across many

machines, we refer to

horizontal cloning. In addition, there are different

scenarios when you use vertical and horizontal cloning.

Warning: Some restrictions apply when cloning Host Publisher. See

Section 19.8, “Restrictions” on page 626 for details.