The Domain Administration Server (DAS) in versions of GlassFish Server prior to version 2.1.1 did not allow multiple applications to be deployed using the same web context root, even if those applications were targeted for different GlassFish Server instances.
This behavior was changed in GlassFish Server 2.1.1 and has been carried forward to version 3.0.1. The GlassFish Server DAS now supports the deployment of applications using the same context root as long as those applications are deployed to different GlassFish Server instances. However, this new DAS support is not sufficiently documented.