One important thing to understand concerns execution modes. There are only two modes:
Portal mode: The service runs embedded in the GateIn. In
this mode a PortalContainer is used.
Standalone mode: The service runs without the portal. For
example, the JCR service can run standalone, and also the eXo Portlet
Container. This mode is used by eXo developers for unit tests. As the
name suggests a StandaloneContainer is
used.