Domain mode breakdown

Managing the application server in the domain mode means, in a nutshell, controlling multiple servers from a centralized single point of control. The servers that are part of the domain can span across multiple machines (or even across the cloud) and they can be grouped with similar servers of the domain to share a common configuration. To make some rationale, we will break down the domain components into two main categories:

• Physical components: These are the domain elements that can be identified with a Java process running on the operating system
• Logical components: These are the domain elements that can span across several physical components

Domain physical components

When you start the application server through the domain.sh script, you will be able to identify the following processes:

• Host controller: Each domain installation contains a host controller. This is a Java process that is in charge of starting and stopping the servers that are defined within the host.xml file. The host controller is only aware of the items that are specific to the local physical installation such as the domain controller host and port and the JVM settings of the servers or their system properties.
• Domain controller: One host controller of the domain (and only one) is configured to act as a domain controller. This means basically two things: keeping the domain configuration (in the domain.xml file) and assisting the host controller with managing the servers of the domain.
• Servers: Each host controller can contain any number of servers which are the actual server instances. These server instances cannot be started autonomously. The host controller is in charge of starting and stopping single servers when the domain controller commands them.

If you start the default domain configuration on a Linux machine, you will see that the following processes will show in your operating system:

As you can see, the process controller is identified by the [Process Controller] label, while the domain controller corresponds to the [Host Controller] label. Each server shows in the process table with the name defined in the host.xml file. You can use common operating system commands such as grep to further restrict the search to a specific process.

Domain logical components

A domain configuration with only physical elements in it would not add much to a line of standalone servers. The following components can abstract the domain definition, making it dynamic and flexible:

• Server Group: A server group is a collection of servers. They are defined in the domain.xml file, hence they don't have any reference to an actual host controller installation. You can use a server group to share configurations and deployments across a group of servers.
• Profile: A profile is an EAP configuration. A domain can hold as many profiles as you need. Out of the box the following configurations are provided:

  * default: This configuration matches with the standalone.xml configuration (in standalone mode), hence it does not include JMS, IIOP, or HA

  * full: This configuration matches with the standalone-full.xml configuration (in standalone mode), hence it includes JMS and OpenJDK IIOP to the default server

  * ha: This configuration matches with the standalone-ha.xml configuration (in standalone mode), so it enhances the default configuration with clustering (HA)

  * full-ha: This configuration matches with the standalone-full-ha.xml configuration (in standalone mode), hence it includes JMS, IIOP, and HA