The server creates one instance, called server at the time of installation. You can delete the server instance and create a new instance with a different name if you prefer.
Each instance has its own Java configuration, Java resources,
application deployment
areas, and server configuration settings. Changes to one instance have
no
effect on other instances.
For many users, one instance meets their needs. However, depending upon your environment, you might want to create one or more additional instances. For example, in a development environment you can use different instances to test different configurations, or to compare and test different application deployments. Because you can easily add or delete an instance, you can use them to create temporary “sandbox” areas to experiment with while developing.
In addition, for each instance you can also create virtual servers. Within a single installed server instance you can offer companies or individuals domain names, IP Addresses, and some administration capabilities. For the users, it is almost as if they have their own web server, without the hardware and basic server maintenance. These virtual servers do not span instances. For more information about virtual servers, see To configure the JVM settings.
In operational deployments, for many purposes you can use virtual servers instead of multiple instances. However, if virtual servers do not meet your needs, you can also use multiple instances.
An instance is not started automatically. Once you start an instance, the instance runs until you stop it. When you stop an instance, it stops accepting new connections, then waits for all outstanding connections to complete. If your machine crashes or is taken offline, the server quits and any requests it was servicing may be lost.
See also: To View Server Instance Information.