A domain is a group of instances that are administered together. However, an application server instance can belong to just one domain. In addition to administration boundary, domain provide a basic security structure whereby different administrators can administer specific groups (domains) of application server instances. By grouping the server instances into separate 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. If the configuration is changed for one domain, the configurations of other domains are not affected.
The Sun Java System Application Server installer creates the default administrative domain (named domain1). It also creates an associated domain administration server (named server). You must provide the administration server port number. The default administration server port is 4849. The installer also queries for the administration username and password. After installation, additional administration domains can be created.