In this unit we are going to look at cloud computing. Cloud computing, also known as 'on-demand computing', is a kind of Internet-based computing, where shared resources, data and information are provided to computers and other devices on-demand. It is a model for enabling ubiquitous, on-demand access to a shared pool of configurable computing resources. Cloud computing and storage solutions provide users and companies with various possibilities for storing and processing their data in third-party data centers It relies on the sharing of resources to achieve coherence and economies of scale, similar to a utility (like the electricity grid) over a network

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Cloud computing is the delivery of computing as a service rather than a product. Computing processing power, shared resources, software, and data are provided to computers and other devices as a service over a network. Cloud computing provides scalable computation, software, data access, and storage resources without even the need for cloud users to know the location and other details of the computing infrastructure. End users access cloud based applications through a web browser or a light weight desktop or mobile app while the business software and data are stored on servers at a remote location. Cloud application providers try to give the same or better service and performance as if the software programs were installed locally on end-user computers.

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Cloud computing providers offer their services according to three fundamental models: • Software as a service (SaaS) • Platform as a service (PaaS), and • Infrastructure as a service (IaaS) IaaS is the most basic service and each of the higher model builds over the lower one abstracting its details and isolating the user from them.

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In the most basic cloud service model, cloud providers offer computers – either physical ones or more often virtual machines; raw (block) storage, firewalls, load balancers, and networks. IaaS providers supply these resources on demand from their large pools installed in data centers. To deploy their applications, cloud users then install operating system images on the machines as well as their application software. In this model, it is the cloud user who is responsible for patching and maintaining the operating systems and application software.

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In the PaaS model, cloud providers deliver a computing platform and/or solution stack which typically includes operating system, programming language execution environment, database, and web server. Application developers can develop and run their software solutions on a cloud platform without the cost and complexity of buying and managing the underlying hardware and software layers and without the burden of having to administer the operating systems and machines.

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In this model, cloud providers install and operate application software in the cloud and cloud users access the software from cloud clients. Wordpress.com, Gmail, Google drive or Office365 are examples of this model.

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Privacy Using a cloud service provider can complicate guaranteeing privacy of data because it is stored and replicated in remote servers whose location is unknown to the user. The cloud provider should guarantee that the privacy requirements of the user are satisfied.

Availability Cloud providers should guarantee their customers that they will have regular and predictable access to their data and applications.

Security The effectiveness and efficiency of traditional protection mechanisms can differ widely from those of traditional architectures

Compliance Cloud providers have business continuity and data recovery plans in place to ensure that service can be maintained in case of a disaster or an emergency and that any data loss will be recovered. In addition to the requirements to which customers are subject, the data centers maintained by cloud providers may also be subject to compliance requirements, for instance between US and the EU.

Legal As several countries can be involved, certain legal issues may arise: everything from trademark infringement to privacy of data. For example, legal problems could arise for a business located in the European Union if it wishes to use a cloud provider that has its servers located in the United States, as the privacy regulations are different.

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