# Model-Driven Approach to Cloud-Portability Issue
## 1 Introduction  
In today's world of information technology (IT) we encounter virtualization in several ways. Whether it is the virtualization of operating systems (OSs), network elements, development platforms or applications. Virtualization of this type is particularly beneficial for service providers because they can provide services to multiple users on one physical device without these services colliding with each other. Virtualization is a way to optimize the usage of physical resource capacities with scalability and flexibility in their allocation. From the end user's point of view, virtualization has virtually no influence on the service itself, because the virtual service has the same behavior as the service that would be executed directly on a physical device. Many times, users do not even notice using a service that is being virtualized. With the evolution of virtualization, we came to a state called Cloud Computing (CC). CC is a relatively new IT industry and has not yet been fully unified and standardized. Currently, several standardization groups are trying to unify the use of CC environments from the perspective of users and providers. We can divide standardization organizations into two groups. In the first group, there are organizations that deal with business relationships between individual participants. We can mention the European Commission and its working groups the Cloud Select Industry Group (C-SIG) and the European Commission Expert group on Cloud Computing Contracts [1, 2]. Another organizationis the European Telecommunications Standards Institute (ETSI) and its Cloud Standard Coordination group [3]. In the second group there are organizations dealing mainly with the technological aspects of CC. We will focus on the three best-known standardization organizations, NIST (National Institute of Standards and Technology), ITU-T (International Telecommunication Union-Telecommunication Standardization Sector) and ISO (International Organization for Standardization). In NIST SP-500-291 [4], CC is defined as a model that enables ubiquitous, practical, network-accessible and on-demand computing resources (such as networks, servers, storage, applications and services) with minimal effort and without interaction with the provider of these resources. This model is composed of five basic features, three service models and four deployment models. The ITU-T in Y.3500 Recommendation defines CC as a paradigm that allows access to a set of shared physical or virtual resources via a network. These resources are scalable and managed by users. This paradigm is composed of key features, user roles, deployment models and cross-sectional CC aspects. A text identical text to Y.3500 was published by ISO as standard ISO/IEC 17788:2014 [5]. Nowadays, CC environments are increasingly being used, mainly at corporate environments. According to [6; 7; 8; 9; 10; 11; 12], more than 80 percent of enterprises and small businesses are using some type of CC. This is mainly Infrastructure as a Service (IaaS) and container technologies. Reasons are different, but one of them could be that CCs significantly save resources or open up new opportunities in providing IT services. With the wider availability and knowledge of CC, users and providers are aware of CC benefits. On the one hand, CC saves resources for providers, because the optimized use of physical devices can meet the requirements of a far greater number of users than on physically dedicating devices. On the other hand, CCs save resources for users who are not forced to buy, operate and manage hardware or software. Providers mostly use the so-called \"pay-as-you-go\" model, where users pay only for those calculating resources that they actually consume. Such a solution is particularly beneficial for larger organizations. They are not forced to manage their own data center and are able to dynamically increase and reduce leased computing power on demand. This can ultimately save a lot of money when properly managed.