Virtual Appliances are a relatively new phenomenon, and expectations vary widely on their use and precise benefits. This paper details some usage models, how requirements vary depending on the environment the appliance runs in, and the challenges connected to them. In particular, appliances for the enterprise have to fit into already existing infrastructure and work with existing sitewide services such as authentication, logging, and backup.
Appliances can be most simply distributed and deployed as binary images; this requires support in existing tools and a metadata format to describe the images. A second approach, basing appliances entirely on a metadata description that includes their setup and configuration, gives users the control they need to manage appliances in their environment.