The microkernel core of the server is a simple, flexible, nested container framework defined in this package.

The container model consists of three primary participants:

- Service - A well-known Java object defined by a Java interface. Code running in the server should be organized into services that perform logical (and limited) blocks of work. These services can then be exposed as a Java interface and obtained using the ServiceLookup service. Although most services will be local to the container, some may use RMI, web services, XMPP, or other remote procedure call technologies to provide services across the network.
- Module - The smallest server deployment unit. A module has a well-defined life cycle that is managed by its hosting container. A module may contain zero or more services and client code that accesses these services. Modules can be deployed and configured individually, allowing the easy implementation of server plugins and on the fly reconfiguration of the server.
- Container - A special module that hosts server modules including other containers. Hosting involves life cycle management of child modules, configuration of child modules, and providing access to shared resources. Containers also provide their own configurable security managers and custom classloaders that extend the classpath to automatically include module classes and jar files located in well defined locations (e.g. similar to WEB-INF/lib and WEB-INF/classes in a J2EE web-app/WAR).

The nesting nature of containers allows a tree-like server architecture with a root 'bootstrap container' with core modules, and child containers with their own modules. Child containers by default inherit and extend the bootstrap container's classpath and services while being protected from implementation details of any modules, containers, or services in layers above them. In some cases, child containers may have restricted views or access to upper levels of the tree (e.g. a user plug-in container that allows users to add arbitrary server extensions).