Many approaches have been developed for modeling the functional aspects of Web applications, but there is a lack of a modeling language for their architectural concerns. This paper proposes such a modeling language defined as a UML 2.0 profile, which allows the specification of domain-specific models for the architectural view of Web applications. The profile is part of the Web Software Architecture (WebSA) approach, which follows the Model Driven Architecture (MDA) principles. The modeling elements proposed for each WebSA model (subsystem, configuration and integration models) are both represented graphically and formalized by means of the profile and the metamodel, respectively. In this article we will focus on the Configuration model and how it is used to model the well-known Petstore example.