For starters, here is a very basic example demonstrating the separation between the code and the deployment of an application and also showing the simplicity with which the deployment can be modified.

As shown in the diagram below, in the first step, The application is just composed of two primitive components distributed into a single Java Virtual Machine.

Now, in order to use two separate Java Virtual Machine, in the deployment descriptor file, the line:

      <host id="localhost" os="unix" hostCapacity="1"
      vmCapacity="2">
    

is changed to:

      <host id="localhost" os="unix" hostCapacity="2"
      vmCapacity="1">
    

Before changing the line, the deployment descriptor indicates that there will have 1 Java Virtual Machine with 2 nodes inside the JVM.

Then, once the changed made, the deployment descriptor specifies that it must have 2 Java Virtual Machines with 1 node per JVM:

All the source files are available at the end of the part in Chapter 31, Annex.