Cloud computing is emerging as a major trend in the ICT industry. While most of the attention of the research community is focused on considering the perspective of the Cloud providers, offering mechanisms to support scaling of resources and interoperability and federation between Clouds, the perspective of developers and operators willing to choose the Cloud without being strictly bound to a specific solution is mostly neglected. We argue that Model-Driven Development can be helpful in this context as it would allow developers to design software systems in a cloud-agnostic way and to be supported by model transformation techniques into the process of instantiating the system into specific, possibly, multiple Clouds. The MODA-CLOUDS (MOdel-Driven Approach for the design and execution of applications on multiple Clouds) approach we present here is based on these principles and aims at supporting system developers and operators in exploiting multiple Clouds for the same system and in migrating (part of) their systems from Cloud to Cloud as needed. MODACLOUDS offers a qualitydriven design, development and operation method and features a Decision Support System to enable risk analysis for the selection of Cloud providers and for the evaluation of the Cloud adoption impact on internal business processes. Furthermore, MODACLOUDS offers a run-time environment for observing the system under execution and for enabling a feedback loop with the design environment. This allows system developers to react to performance fluctuations and to redeploy applications on different Clouds on the long term.

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Cloud Platform as a Service (PaaS) is a rapidly growing IT paradigm which enables software developers to deploy applications without the burden of software platform maintenance. Currently, the PaaS market is dominated by a few providers that promote incompatible standards. This introduces adoption barriers that prevent the interoperability between heterogeneous PaaS offerings, so software developers are not able to manage distributed applications spanning multiple public/private clouds. In this paper we present a multi-PaaS application management solution as a result of the Cloud4SOA European project that addresses these challenges. To clarify this approach a distributed deployment and cloud bursting scenarios are used.

Abstract.We present the open reference architecture of the SeaClouds solution. It aims at enabling a seamless adaptive multi-cloud management of complex applications by supporting the distribution, monitoring and reconfiguration of app modules over heterogeneous cloud providers. Motivation and Objectives of SeaCloudsCloud computing is a model for enabling convenient and on-demand network access to a shared pool of configurable computing resources that can be rapidly provisioned and released with minimal management effort or service provider interaction. Many private and public clouds have emerged during the last years, offering a range of different services at SaaS, PaaS levels aimed at matching different user requirements. Current cloud technologies suffer from a lack of standardization, with different providers offering similar resources in a different manner, which results in the vendor lock-in problem. This problem affects all stages of the cloud applications' lifecycle, ranging from their design to their operation. Application developers must know the features of the services to be used, and have a deep knowledge of the providers' API. To reduce the need of using deep knowledge, we can find solutions based on the use of standards, such as OASIS CAMP or OASIS TOSCA , DMTF CIMI , unified APIs, such as jClouds 5 , or solutions like Docker 6 . These solutions are indeed very different, for example, whereas jClouds provides a cloud agnostic API library to provision and configure secure communications with cloud virtual machines, container-based solutions like Docker allow describing and deploying applications and their dependencies through containers on machines with the corresponding engine. Furthermore, different vendors (e.g., Dell, BMC, Abiquo) are currently commercialising tools for This work has been partly supported by the EU-FP7-ICT-610531 SeaClouds project. 5 https://jclouds.apache.org 6 https://www.docker.com

Cloud Platform as a Service (PaaS) is a novel paradigm that enables software developers to create (develop or integrate), deploy, execute, and manage business applications, using a service provided by a third party. The diversity and heterogeneity of the existing PaaS offerings raises several interoperability challenges. The actual Platform as a Service market is still quite young, chaotic and highly fragmented, dominated by a few providers which use and promote incompatible standards and formats. This introduces adoption barriers due to the lock-in issues that prevent the portability of data and software from one PaaS to another. Moreover, software developers do not only need to deploy applications into a specific Cloud platform, but also to migrate applications from one Cloud platform to another, and to manage distributed applications spanning multiple PaaS. In this paper, we present a multi-cloud PaaS management as a result of the Cloud4SOA European project that addresses these challenges.