cloud computing, scalability, horizontal scalability, vertical scalability, systematic mapping.

Cloud computing has gained popularity in the industry due to the expansion of data generation from various domains such as physics, sciences, business and so on. Scalability can play an essential role in clouds and can improve their performance. The importance of scalability lies in its ability to cope with the increasing workloads by adding additional resources when demand increases. Typically, there are two types of scalability, namely horizontal scalability and vertical scalability. Hence, there are different classifications of scalability in the literature. This thesis is intended to be a comprehensive survey covering all available scalability techniques in cloud including different classifications based on different criteria. This study basically investigated vertical and horizontal scalability methods. In addition, it explores the used technologies for both of them. Moreover, it determines the amount of research publications related to scalability from different perspectives. To reach the specified goal, a systematic mapping study has been done about scalability.