The concept of ―Cloud‖ is not a new one and it has been used in several fields such as Automated Teller Machine‘s networks in 1990s. The term of ―Cloud‖ is used to describe the networks that incorporate various technologies, without the user knowing it. In 1997, as the first academic definition, Chellapa clarified cloud computing as ―a computing paradigm where the boundaries of computing will be determined rationale rather than technical‖ [42].
Figure 2-1 Cloud Computing Definition [43].
The National Institute of Standards and Technology (NIST) proposed a cloud computing definition as follows: ―Cloud computing is a model for enabling convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers,
Community Cloud
Private
Cloud Public Cloud
Hybrid Clouds Deployment Models Service Models Essential Characteristics Common Characteristics Software as a Service (SaaS) Platform as a Service (PaaS) Infrastructure as a Service (IaaS) Resource Pooling
Broad Network Access Rapid Elasticity
Measured Service
On Demand Self-Service
Low Cost Software
Virtualization Service Orientation
Advanced Security
Homogeneity
Massive Scale Resilient Computing
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storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction. This cloud model promotes availability and is composed of five essential characteristics, three service models, and four deployment models‖ [11][41]
.
Figure 2-1 shows the framework introduced by NIST to define cloud computing [43].
According to the different perspectives of various corporations such as; academicians, architects, consumers, developers, engineers and managers, there are several definitions for cloud computing [44]. Table 2-1 provides some available cloud definitions.
Table 2-1 Cloud Computing definitions. Reference Author(s) Year Definition/Excerpt
[42] Chellapa 1997 ―a computing paradigm where the boundaries of computing will be determined rationale rather than technical‖
[41] NIST 2009
―Cloud computing is a model for enabling convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction. This cloud model promotes availability and is composed of five essential characteristics, three service models, and four deployment models‖
[45] Bernstein et al. 2009
―Cloud Computing is a datacenter which:
Implements a pool of computing resources and services which are shared amongst subscribers.
Charges for resources and services using an ―as used‖ metered and/or capacity based model.
Are usually geographically distributed, in a manner which is transparent to the subscriber (unless they explicitly ask for visibility of that).
Are automated in that the provisioning and configuration (and de- configuration and unprovisioning) of resources and services occur on the ―self service‖, usually programmatic request of the subscriber, occur in an automated way with no human operator assistance, and are delivered in one or two orders of seconds.
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Reference Author(s) Year Definition/Excerpt
Resources and services are delivered virtually, that is, although they may appear to be physical (servers, disks, network segments, etc) they are actually virtual implementations of those on an underlying physical infrastructure which the subscriber never sees.
The physical infrastructure changes rarely. The virtually delivered resources and services are changing constantly.‖
Resources and services may be of a physical metaphor (servers, disks, network segments, etc) or they may be of an abstract metaphor (blob storage functions, message queue functions, email functions, multicast functions, etc). These may be intermixed.
[46] Gartner 2009
―A style of computing where scalable and elastic IT-related capabilities are provided as-a-service using Internet technologies to multiple external customers‖
[15] University of Berkeley 2009
―Cloud Computing refers to both the applications delivered as services over the Internet and the hardware and systems software in the datacenters that provide those services‖
[47] Berger 2008
―... the key thing we want to virtualise or hide from the user is complexity. ...with cloud computing our expectation is that all that software will be virtualised or hidden from us and taken care of by systems and /or professionals that are somewhere else – out there in the cloud‖.
[48] Buyya et al. 2008
―A Cloud is a type of parallel and distributed system consisting of a collection of interconnected and virtualized computers that are dynamically provisioned and presented as one or more unified computing resources based on service-level agreements established through negotiation between the service provider and consumers‖
[48] Buyya et al. 2008
―a type of parallel and distributed system consisting of collection of interconnected and virtualised computers that are dynamically provisioned and present on or more unified computing resource based on service-level agreements established through negotiation between
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Reference Author(s) Year Definition/Excerpt
service provider and customer‖.
[49] Catteddu & Hogben 2009
―on-demand service model for IT provision, often based on virtualisation and distributed computing technologies‖
[47] Cohen 2008
―for me the simplest explanation for cloud computing is describing it as, ‗internet centric software‘. This new cloud computing software model is a shift from traditional single tenant approach to software development to that of scalable, multi-tenant, multi- platform, multi- network, and global‖.
[47] Doerksen 2008 ―cloud computing is... the user friendly version of grid computing‖.
[47] Edwards 2008
―...what is possible when you leverage web scale infrastructure (application and physical) in an on-demand way. ...anything as a service... all terms that couldn‘t get it done. Call it ‗cloud‘ and everyone goes bonkers‖.
[47] Eicken 2008 ―... outsourced, pay-as-you-go, on-demand, somewhere in the internet‖.
[50]
Forrester Research,
Inc.
2008
―A pool of abstracted, highly scalable, and managed compute infrastructure capable of hosting end-customer applications and billed by consumption‖
[51] Gartner, Inc. 2008
―A style of computing where massively scalable IT-enabled capabilities are de- livered as a service to external customers using Internet technologies.‖
[47] Gaw 2008 ―refers to the bigger picture...basically the broad concept of using the internet to allow people to access technology enabled services‖.
[47] Gourlay 2008 ―cloud will be the next transformation over the next several years, building off of the software models that virtualisation enabled‖
[47] Haff 2008 ―...there are really only three types of services that are cloud based: SaaS, PaaS, and Cloud Computing Platforms‖.
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Reference Author(s) Year Definition/Excerpt
[47] Harting 2008
―cloud computing overlaps some of the concepts of distributed, grid and utility computing, however it does have its own meaning if contextually used correctly. Cloud computing really id accessing resources and services needed to perform functions with dynamically changing needs‖.
[47] Kaplan 2008
―a broad array of web-based services aimed at allowing users to obtain a wide range of functional capabilities on a ‗pay-as-you-go‘ basis that previously required tremendous hardware/software investment and professional skills to acquire‖.
[47] Kepes 2008 ―put cloud computing is the infrastructural paradigm shift that enables the ascension of SaaS‖.
[47] Klems 2008
―you can scale your infrastructure on demand within minutes or even seconds, instead of days or weeks, thereby avoiding under- utilisation(idle servers) and over utilisation (blue screen)of in-house resources‖.
[52] LizheWang & Laszewski 2008
―a set of network enabled services, providing scalable, QoS guaranteed, normally personalised, inexpensive computing platforms on demand, which could be accessed in a simple and pervasive way‖
[47] Martin 2008
―cloud computing really comes into focus only when you think about what IT always needs: a way to increase capacity or add capabilities on the fly without investing in new infrastructure, training new personnel, or licensing new software‖
[47] Pritzker 2008 ―cloud tend to be priced like utilities... i think is a trend not a requirement‖. 2008
[47] Ricadela 2008 ―... cloud computing projects are more powerful and crash proof than Grid systems developed even in recent years‖
[47] Sheedan 2008 ―... ‗cloud pyramid‘ to help differentiate the various cloud offerings out there... top: SaaS; middle: PaaS; bottom: IaaS‖.
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Reference Author(s) Year Definition/Excerpt
[47] Sheynkman 2008
―the ‗cloud‘ model initially focused on making hardware layer consumable as on- demand compute and storage capacity. ... to harness the power of the cloud, complete application infrastructure needs to be easily configured, deployed, dynamically scaled and managed in these virtualised hardware environments‖.
[47] Sultan 2008
―... in a fully implemented Data center 3.0 environment, you can decide if an app is run locally (cook at home), in someone else‘s data center (take-out) and you can change your mind on the fly in case you are short on data center resources (pantry is empty) or you having environmental/facilities issues (too hot to cook)‖.
[53] Vaquero et al. 2009
―cloud are a large pool of easily usable and accessible virtualised resources (such as hardware, development platforms and/or services). These resources can be dynamically reconfigured to adjust a variable load (scale), allowing also for an optimum resource utilisation. This pool of resources is typically exploited by a pay-per-use model in which guarantees are offered by the infrastructure provider by means of customised SLAs‖