The Kernel startup follows a well-defined sequence to load configuration files. The objects are initialized in the container only after the whole loading sequence is done. Hence, by placing your configuration in the upper location of the sequence, you can override a component declaration by yourself. You will typically do this when you want to provide your own implementation of a component, or declare custom init-params.
The external-component-plugins declarations are additive, so it is NOT possible to override them.
Configurations for the RootContainer are loaded first, and then for the PortalContainers.
Services default RootContainer configurations from JAR files: /conf/configuration.xml.
External RootContainer configuration will be found at $exo.conf.dir/configuration.xml.
Services default PortalContainer configurations from JAR files: /conf/$PORTAL/configuration.xml.
Web applications configurations from WAR files /WEB-INF/conf/configuration.xml.
External configuration for services of the portal will be found at $exo.conf.dir/portal/$PORTAL/configuration.xml.
$exo.conf.dir is a system property which points to the folder containing external configuration files on the file system. It is passed to the JVM in the startup script like -Dexo.conf.dir=gatein.
$PORTAL is the name of the portal container. By default, the name "portal" is unique.