  A Geant4-based simulation framework for rare event searching experiments with
germanium detectors named SAGE is presented with details. It is designed for
simulating, assessing background distribution, and investigating the response
of the germanium detectors. The SAGE framework incorporates its
experiment-specific geometries and custom attributes, including the event
generators, physics lists and output format, to satisfy various simulation
objectives. Its docker image has been prepared for virtualizing and
distributing the SAGE framework. Deployment of a Geant4-based simulation will
be convenient under this docker image. The implemented geometries include
p-type point contact and broad energy germanium detectors with environmental
surroundings, and these hierarchical geometries can be easily extended. Users
select these custom attributes via the JSON configuration files. The
aforementioned attributes satisfy the simulation demands and make SAGE a
generic and powerful simulation framework for the CDEX experiment.
