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Top1. Introduction
Cloud computing is a paradigm that has emerged and attracted particular attention in recent years. The National Institute of Standards and Technology (NIST) defines this paradigm as a model that allows access over a network in a simple way and on demand to a set of shared and configurable computer resources like networks, servers, storage, applications and services. In just over a decade, the cloud has become one of the fastest-growing IT markets with the best margins. Since it is more flexible and less expensive than traditional computing, more and more companies are using the cloud to run their applications, use online software, store or analyze their data. Customers who use “public clouds” like Amazon, Google, or Microsoft pay according to the amount of storage or power used. If the company wants to keep control of its entire system, it can create a “private cloud”, entirely customized, which will be dedicated to it alone, but will be more expensive. Indeed, Cloud improves the flexibility and agility of a company. IT resources are flexible and can be defined precisely according to the fluctuation of needs related to the activity. The implementation of new applications is fast and cheap. Several companies are outsourcing more and more parts of their global IT infrastructure to a private or public cloud. Using a cloud service is associated with a multitude of benefits; a particularly high computing power is offered by allowing delocalization of data processing and thus takes advantage of all the possibilities and performances made available to them by the cloud server. Constant monitoring of the development of resources allocated to the Cloud service and real-time information on the use of the Cloud platform are allowed. Furthermore, Cloud computing represents a very significant cost saving, it allows companies to reduce their heavy investments in hardware and software solutions especially small companies who pay only the storage space they need. As a result, cloud computing will become ubiquitous in the lives of most companies. Since Cloud usage is growing rapidly and users are becoming more demanding in terms of Quality of Service (QoS), data storage capacity on the cloud has grown exponentially. Cloud storage providers are starting to deploy more data centers with greater storage capacity and must be able to dynamically adjust their hosting capabilities in response to changing workload and QoS requirements. Cisco (Bernstein et al, 2009) proposed a solution to overcome the limitation of resources and satisfy user requirements and defined a new cloud vision called “Cloud of Clouds” by introducing the concept of “Inter-Clouds”. Cloud actors can benefit from different Inter-Cloud models that differ in initiator and degree of collaboration, among these models: Hybrid Clouds, Multi-Clouds and Cloud Federations. Many companies in fact need a “hybrid” system, combining the cost, power and flexibility of the public “cloud” and the security of the private “cloud”. Some draw from different public cloud providers: for example, Amazon for infrastructure or Google for data analysis. Several recent works (Rebai, 2017; Ferrer 2012) have suggested different inter-cloud architectures for interoperability and cooperation between clouds, providers can freely allocate their charges between separate clouds to meet requirements, while users can easily migrate their services to appropriate providers whenever needed. According to the initiator of the inter-Clouds, two use scenarios can be distinguished, Cloud federation and Multi-Cloud (Grozev et al, 2012). While resource aggregation is initiated and managed by end users in multi-cloud scenarios, Cloud federation is a heterogeneous set of interconnected clouds (Assis et al, 2016), it is referred to as provider-centric interoperability (Rebai, 2017) and the cooperation between providers is voluntary and based on previous trade agreements. Till now, the number of properties that must be present in a cloud federation is not determined. The authors in (Assis et al, 2016) consider the integrity of the environment, the Federation Level Agreement (FLA), and the voluntary aspect of federation members as the minimal subset of properties that distinguishes cloud federation from other inter-cloud organizations. However, in the literature, no cloud federation architecture presents the cloud federation management aspect or implements this minimal subset of properties.