Cloud patterns are described as good solutions to recurring design problems in a cloud context. These patterns are often inherited from Service Oriented Architectures or Object-Oriented Architectures where they are considered good practices. However, there is a lack of studies that assess the benefits of these patterns for cloud applications. In this paper, we conduct an empirical study on a RESTful application deployed in the cloud, to investigate the individual and the combined impact of three cloud patterns (i.e., Local Database proxy, Local Sharding-Based Router and Priority Queue Patterns) on Quality of Service (QoS). We measure the QoS using the application's response time, average, and maximum number of requests processed per seconds. Results show that cloud patterns doesn't always improve the response time of an application. In the case of the Local Database proxy pattern, the choice of algorithm used to route requests has an impact on response time, as well as the average and maximum number of requests processed per second. Combinations of patterns can significantly affect the QoS of applications. Developers and software architects can make use of these results to guide their design decisions.