The container package is responsible of building a hierarchy of containers. Each service will then be registered in one container or the other according to the XML configuration file it is defined in. It is important to understand that there can be several PortalContainer instances that all are children of the RootContainer.

The behavior of the hierarchy is similar to a class loader one, hence when you will lookup a service that depends on another one, the container will look for it in the current container and if it cannot be found, then it will look in the parent container. That way you can load all the reusable business logic components in the same container (here the RootContainer) and differentiate the service implementation from one portal instance to the other by just loading different service implementations in two sibling PortalContainers.

Therefore, if you look at the Portal Container as a service repository for all the business logic in a portal instance, then you understand why several PortalContainers allows you to manage several portals (each one deployed as a single war) in the same server by just changing XML configuration files.

The default configuration XML files are packaged in the service jar. There are three configuration.xml files, one for each container type. In that XML file, we define the list of services and their init parameters that will be loaded in the corresponding container.