Software >> Middleware >> Weblogic >> 11gR1 >> What is the minimum server instance needed in a domain

A domain is the basic administration unit for Oracle Weblogic Server.  It consists of one or more Oracle Weblogic Server instances and logically related resouces and services that are managed collectively as one unit.
 

A domain can have one server instance only, in which case it will function both as the administration and managed server