The central piece is the Configuration Admin Service, that beside implementing the OSGi specification it is itself dynamically assembled from the installed configuration providers, persisters and selectors. And does all of this in a dynamic way meaning that you can add/remove/update any of them at runtime triggering system re-configuration. The provider themselves are also dynamic as for example in the case of File System Provider when a modification of a configuration file will trigger an update of the configuration for the targeted managed service (factory).
Configuration Provider
Configuration providers are the source of configuration properties for the registered ManagedService and ManagedServiceFactory.
Configuration Persister
Configuration persisters, as you may guessed, store created / updated configurations.
Configuration Selector
As there can be more configurations available at the same time for the same configuration target (same persistent identifier = PID), configuration selector role is to select / choose the one to be considered active. The default selector will select configurations by their time stamp.
Properties Adapters
The role of properties adapters is to transform divers sources of configuration properties into a simple Map of property names -> values.