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Platform as a Service (PaaS) is a category of cloud computing services that provides a platform allowing customers to develop, run and manage Web applications without the complexity of building and maintaining the infrastructure typically associated with developing and launching an app. Although an standard definition of PaaS is not available, according to National Institute of Standards and Technology (NIST), PaaS is a system that provides the capability to the con- sumer to deploy onto the cloud infrastructure consumer languages, libraries, services and tools supported by the provider. The consumer does not manage or control the underlying cloud infra- structure including network, servers, operating systems, or storage, but has control over the de-

Questions for CloudTeams:

1. Which bug tracking software shall be connected with CloudTeams?

Questions for CloudTeams:

1. Does CloudTeams implement a specific development cycle

2. Does CloudTeams provide collaboration and social abilities to all points of a devel- opment cycle?

3. Are these Tools providing APIs in order to be encapsulated in CloudTeams? 4. Are the collaboration and social abilities of the selected tools sufficient?

Notable cases:

ployed applications and possibly configuration settings for the application hosting environment (Peter Mell, Timothy Grance. 2011).

In order to make the definition of PaaS clearer, we should briefly present the different cloud lay- ers. As presented in Figure 8, there are usually 3 layers that describe different approaches in cloud definition.

Figure 8: Cloud Layers

On the presented Figure 8, from bottom up, Infrastructure as a service (IaaS) refers to the under- lying hardware resources such as network, storage and compute resources, usually with some virtualization technology39. While the advent of IaaS opened new territory for businesses to bet- ter manage IT hardware costs, it put developers in a challenging situation. Developers on IaaS are responsible for more of the operational work during development and test. They have to de- velop skills to provision, configure, manage and update hardware resources that they would have never needed in a traditional model.

In a PaaS environment, the service provider not only is responsible for provisioning and manag- ing the lower level infrastructure resources, but also for providing a fully managed application development and deployment platform. PaaS provides the developers with the appropriate ver- sion of operating systems, databases, middleware, software tools and managed services, usually in a multitenant environment. The biggest added value of PaaS is that developers are completely abstracted from the lower-level details of the environment, so they can fully focus on what there are really good at (rapid development and deployment) and not worry about things like scalabil- ity, security and more that are fully managed by PaaS.

Finally, on the top, Software as a service (SaaS) refers to the actual functional applications con- sumable on-demand by application developers, usually made available through PaaS as a cata- logue or a marketplace40.

Thus, as PaaS abstract low level details of the environment, is the best option for developers that want to easily deploy applications for testing or production reasons. And also this makes PaaS platforms ideal for automated deployments, for a single developer or for development teams.

39 http://www.thoughtsoncloud.com/2014/02/what-is-infrastructure-as-a-service-iaas/ 40 http://www.thoughtsoncloud.com/2014/02/what-is-platform-as-a-service-paas/

PaaS platforms are reaching high levels of interest41 _{and conclude a market of continuous grows.}

Some of the major players on PaaS market are

•   CloudFoundry42 is an open source PaaS solution that provides a choice of clouds, frame- works and application services. As an open source project, there is a broad community both contributing and supporting Cloud Foundry.

•   IBM Bluemix43 is PaaS developed by IBM, and is based on Cloud Foundry. It supports sev- eral programming languages and services as well as integrated DevOps to build, run, deploy and manage applications on the cloud. BlueMix supports Java, Node.js, Ruby and can be extended to support other languages such as PHP, Python or Scala

•   Stackato44 is a commercially supported PaaS that is built on top of open source components such as Cloud Foundry and Docker that runs on top of different cloud infrastructures. Stack- ato automatically configures the required language runtimes, web frameworks, data and messaging services.

•   Red Hat OpenShift45 is an open source PaaS project that utilizes proven open source tech- nologies to deliver the benefits of efficiency and accelerated application delivery in a PaaS architecture. OpenShift Origin is developed by a community ecosystem including Red Hat, Accenture, PayPal, Cisco and others.

•   Heroku46 is a PaaS platform that provides the tools needed to iterate quickly and adopt the right technologies for users' projects. It allows developers to build modern, maintainable apps and instantly extend them with functionality from hundreds of cloud service providers without worrying about infrastructure.

•   AWS Beanstalk47 is a PaaS platform offered by Amazon that allows users to deploy and manage applications in the AWS cloud without worrying about the infrastructure that runs those applications. AWS Elastic Beanstalk reduces management complexity without re- stricting choice or control.

•   Microsoft Azure48 is a PaaS platform offered by Microsoft that enables developers to build and run highly available applications without focusing on the infrastructure. It provides au- tomatic OS and service patching, built in network load balancing and resiliency to hardware failure.

•   Apache Stratos49 is a polyglot, open source PaaS framework with ready-made cartridges that bring scalability, resource-sharing and self-service to Tomcat servers, MySQL and PHP containers.

•   CloudControl50 is a PaaS based in Germany that aims to serve the European tech communi- ty through offering of multi-language support and no vendor lock-in.

41 http://redmonk.com/sogrady/2013/09/19/paas-questions/ 42 http://www.cloudfoundry.org 43 http://www.ibm.com/cloud-computing/bluemix 44 http://www.activestate.com/stackato 45 http://openshift.redhat.com/ 46 https://www.heroku.com/ 47 http://aws.amazon.com/elasticbeanstalk/ 48 http://azure.microsoft.com 49 http://stratos.apache.org/ 50 https://www.cloudcontrol.com/

•   Google App Engine51 is Google's PaaS for deploying apps on Google infrastructure. Google offers automatic scaling, load balancing, persistent storage and integration with other Google cloud services. App Engine also offers a free SDK for multiple languages.

Extended analysis of popular PaaS platforms, on the basis of this table is provided in Annex IV in paragraph 5.4.

The selection of the best suited PaaS platform is not a trivial task, as the market is still relative young, with the PaaS platforms having key differentiations, both in terms of offered services and limitations or requirements. This raises the issue of interoperability between different PaaS plat- forms and the possibility of vendor lock in.

Interoperability refers to the ability of a collection of communicating entities to share specific

information and operate on it according to agreed-on operational semantics (Lisa Brownsword et al., 2004). The Use Case Cloud Computing Discussion Group defines Cloud computing interop- erability “as the ability to write code that works with more than one Cloud provider simultane- ously, regardless of the differences between the providers”. Interoperability is also considered as a synonym of integration “enabling products/software components to work with or integrate with each other seamlessly, in order to achieve a desired result. This is enabled by either integrating through standard interfaces or by means of a broker that converts one product interface to anoth- er (Nikolaos Loutas et al., 2011). However no common standards are used from PaaS platforms yet, some initiatives have proposed solution on portability on PaaS layer.

•   The Topology and Orchestration Specification for Cloud Applications (Tosca)52 is an OASIS project towards enhancing the portability of cloud applications and services. TOSCA provides a standard language to describe the topology of cloud based services, components, relationships and the processes that manage them as well as the lifecycle man- agement of these services (e.g., deploy, patch, shutdown).

•   Cloud Application Management for Platforms (CAMP)53 is a project aimed at defining the interoperability standard of managing applications in PaaS environments. CAMP defines the artefacts and APIs that should be offered by a PaaS offering for managing the building, run- ning, administration, monitoring and patching of applications in the cloud. By defining arte- facts and formats that can be used by any conforming PaaS, CAMP allows independent vendors to create tools and services that interact with any conforming PaaS using the de- fined interfaces.

•   Cloud4SOA54 is a completed FP7 project that focuses on resolving the interoperability and portability issues existing in current Clouds infrastructures and on introducing a user-centric approach for applications which are built upon and deployed using Cloud resources. Cloud4SOA has produced a Semantic Model that is used through project layers. The Cloud4SOA semantic model is an ontology designed to enable PaaS semantic compatibility and interoperability among the different and usually incompatible PaaS offerings, through the Cloud4SOA platform.In support of the Cloud4SOA ontology model, Cloud4SOA also created other classes, and some of them represent a common, harmonized API offering a seamless interconnection and management over the various PaaS offerings. Moreover, the

51 https://appengine.google.com/

52 http://docs.oasis-open.org/tosca/TOSCA/v1.0/os/TOSCA-v1.0-os.html 53 http://docs.oasis-open.org/camp/camp-spec/v1.1/camp-spec-v1.1.html 54 http://www.cloud4soa.com

API can be seen as a mediator between the PaaS offerings and Cloud4SOA system. The harmonized API is able to handle the heterogeneous provider APIs. Adaptors help to trans- late the functions between the harmonized API of the Cloud4SOA and the API of the PaaS vendors (Kamateri, Loutas, & Zeginis, 2013).

•   Another attempt for provision of Cloud interoperability and is made from PaaSport pro- ject55. PaaSport is an active project that continues the vision of Cloud4SOA and extends it with more functionalities, as it focuses on resolving the data and application portability is- sues that exist in the PaaS market through a flexible and efficient deployment and migration approach.

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