1.1 CLOUD COMPUTING IN A NUTSHELL

 

• Technologies such as cluster, grid, and now, cloud computing, have all aimed at allowing access to large amounts of computing power in a fully virtualized manner, by aggregating resources and offering a single system view.
• The aim of these technologies has been delivering computing as a utility.
• Utility computing describes a business model for on-demand delivery of computing power; consumers pay providers based on usage (“payas-you-go”), similar to the way in which we currently obtain services from traditional public utility services such as water, electricity, gas, and telephony.
• Cloud computing has been coined as an umbrella term to describe a category of sophisticated on-demand computing services initially offered by commercial providers, such as Amazon, Google, and Microsoft. 
• Cloud computing denotes a model on which a computing infrastructure is viewed as a “cloud,” from which businesses and individuals access applications from anywhere in the world on demand.
• The main principle behind this model is offering computing, storage, and software “as a service.”

Many practitioners in the commercial and academic spheres have attempted to define exactly what “cloud computing” is and what unique characteristics it presents.

Buyya et al. [2] have defined it as follows: 

“Cloud is a parallel and distributed computing system consisting of a collection of inter-connected and virtualised computers that are dynamically provisioned and presented as one or more unified computing resources based on service-level agreements (SLA) established through negotiation between the service provider and consumers.”

Vaquero et al. [3] have stated 

“clouds are a large pool of easily usable and accessible virtualized resources (such as hardware, development platforms and/or services). These resources can be dynamically reconfigured to adjust to a variable load (scale), allowing also for an optimum resource utilization. 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 customized Service Level Agreements.” 

A recent McKinsey and Co. report [4] claims that 

“Clouds are hardware based services offering compute, network, and storage capacity where: Hardware management is highly abstracted from the buyer, buyers incur infrastructure costs as variable OPEX, and infrastructure capacity is highly elastic.” 

A report from the University of California Berkeley [5] summarized the key characteristics of cloud computing as: "

1. the illusion of infinite computing resources; 
2. the elimination of an up-front commitment by cloud users; and 
3. the ability to pay for use ... as needed ...” 

The National Institute of Standards and Technology (NIST) [6] characterizes cloud computing as 

“... a pay-per-use model for enabling available, convenient, on-demand network access to a shared pool of configurable computing resources (e.g. networks, servers, storage, applications, services) that can be rapidly provisioned and released with minimal management effort or service provider interaction.” 

In a more generic definition, Armbrust et al. [5] define cloud as the 

“data center hardware and software that provide services.” Similarly, Sotomayor et al. [7] point out that “cloud” is more often used to refer to the IT infrastructure deployed on an Infrastructure as a Service provider data center. 

While there are countless other definitions, there seems to be common characteristics between the most notable ones listed above, which a cloud should have: 

1. (i) pay-per-use (no ongoing commitment, utility prices); 
2. (ii) elastic capacity and the illusion of infinite resources; 
3. (iii) self-service interface; and 
4. (iv) resources that are abstracted or virtualised. 

In addition to raw computing and storage, cloud computing providers usually offer a broad range of software services. They also include APIs and development tools that allow developers to build seamlessly scalable applications upon their services. The ultimate goal is allowing customers to run their everyday IT infrastructure “in the cloud.”

Indeed, the long-held dream of delivering computing as a utility has been realized with the advent of cloud computing [5]. However, over the years, several technologies have matured and significantly contributed to make cloud computing viable.