This enhancement request, although is geared towards a use case in Eclipse Virgo, should be useful in other circumstances.

Eclipse Virgo has a capability, called medic, that allows OSGi bundles to define their own logback.xml. To configure loggers and appenders.

Appenders, though, need to be fragments. Fragments to logback, though, need to be applied within the Eclipse Virgo "kernel region" whereas the application bundles are in the "user region" and this presents a configuration challenge as one now needs to muck with the Virgo configuration files.

A more dynamic method of registering appender implementations could be supported if logback provided a mechanism to define an appender factory implementation. Given a class name the factory (which itself could be a generic fragment attached to the logback bundle in the kernel region) could look up any registered appender implementations, instantiate and return the appender.

Happy to discuss the motivation and ideas further...