We present our work on modeling distributed ensembles of virtual appliances (DEVAs) on Infrastructure as a Service (IaaS) clouds. Designing solutions on IaaS providers require a good under standing of the underlying details such as the software installation or the network configuration. We propose the use of DEVAs, a modeling approach built on top of the notion of virtual appliances, that allows easy-to-compose and ready-to-use cloud application architectures that are IaaS-agnostic, and that abstract away unnecessary details for web application developers. In this paper, we extend the definition of a DEVA from previous work by presenting an underlying metamodel and how that metamodel can be transformed to an actual deployment. We also present a case study where we model a web application architecture and we discuss how we can instantiate it in an IaaS cloud. We argue that the DEVA modeling approach is suitable for typical cloud use cases.