An administrative domain (or simply domain) is a group of server instances that are administered together. A server instance belongs to a single administrative domain. The instances in a domain can run on different physical hosts.
You can create multiple domains from one installation of the Application Server. By grouping server instances into domains, different organizations and administrators can share a single Application Server installation. Each domain has its own configuration, log files, and application deployment areas that are independent of other domains. Changing the configuration of one domain does not affect the configurations of other domains. Likewise, deploying an application on a one domain does not deploy it or make it visible to any other domain. At any given time, an administrator can be authenticated to only one domain, and thus can only perform administration on that domain.
A domain has one Domain Administration Server (DAS), a specially-designated application server instance that hosts the administrative applications. The DAS authenticates the administrator, accepts requests from administration tools, and communicates with server instances in the domain to carry out the requests.
The administration tools are the asadmin command-line utility and the browser-based Admin Console. The Application Server also provides a JMX-based API for server administration. The administrator can view and manage a single domain at a time, thus enforcing secure separation.
Since the DAS is an application server instance, it can also host J2EE applications for testing purposes. However, do not use it to host production applications. You might want to deploy applications to the DAS, for example, if the clusters and instances that will host the production application have not yet been created.
The DAS keeps a repository containing the configuration of each domain and all the deployed applications. If the DAS is inactive or down, there is no impact on the performance or availability of active server instances, however administrative changes cannot be made. In certain cases, for security purposes, it may be useful to intentionally stop the DAS process; for example to freeze a production configuration.
Administrative commands are provided to backup and restore domain configuration and applications. With the standard backup and restore procedures, you can quickly restore working configurations. If the DAS host fails, you must create a new DAS installation to restore the previous domain configuration. For instructions, see Recreating the Domain Administration Server in Sun Java System Application Server Enterprise Edition 8.2 Administration Guide.
Sun Cluster Data Services provides high availability of the DAS through failover of the DAS host IP address and use of the Global File System. This solution provides nearly continuous availability for DAS and the repository against many types of failures. Sun Cluster Data Services are available with the Sun Java Enterprise System or purchased separately with Sun Cluster. For more information, see the documentation for Sun Cluster Data Services.