Cloud Computing: A Quick Review
The term cloud computing defines itself a type of computing that relies on sharing computing resources rather than a personal server or devices to handle the applications. The word “cloud” is used as a metaphor for Internet and the phrase “cloud computing” defines Internet based commuting that integrates different services such as servers, storage and applications etc. It can be defined as a centralized storage of huge no. of remote servers having network connectivity allow on-line access for computer services and resources. Cloud computing services can be represented in four ways. These are Software as a service (SaaS), Platform as a service (PaaS), Infrastructure as a service (IaaS), and business process as a service (BPaaS). SaaS uses the web to develop applications owned by a third party vendor, whose interface is accessed by client side. A complete software application is delivered to the end-users including the associated data and hosted centrally in the cloud. The data can be accessed anywhere through the web browser. PaaS includes software platform including infrastructure elements such as database, middleware, security, and presentation layer to develop custom applications. It allows the users for development and testing of applications in a simple cost effective way whereas the resources are managed and controlled by a third party vendor. IaaS is known as the basic service model of cloud. The company provides resources in terms of servers, network bandwidth, and storage space on pay per use basis. BPaaS provides an external web enabled service for external business process. The general architecture of cloud computing is shown in Figure 1.
Figure 1. Architecture of cloud computing
The deployment models of cloud computing can be classified as Public, Private, Hybrid, and Community cloud. The deployment model of cloud computing is shown in Figure 2. Private clouds are meant for private usage and owned by a single company located either inside the campus or outside the campus. It can be owned by an external third party that provides a virtual infrastructure for applications and communications for internal business users. Private cloud offers the benefit of on-demand infrastructure with dedicated resources to an organization. But the computing resources are shared across the applications and business units of those applications. This model is highly suitable for enterprisers with strong concern about data security and data privacy. Public cloud is meant for the public users to access over a network and owned by a third party vendor. Unlike private cloud, the public cloud customers never need provision, manage, upgrade or replace any hardware. Of course, pricing depends on the company’s utility-style. They pay only for resources they reserve or consume during a defined time span. Hybrid cloud enjoys the benefits of both the private and public cloud. It maintains data confidentiality in private cloud and extends the flexible access for public cloud by offering services provided by public clouds. Community Clouds are collaborative resources shared by different organizations with common interest-most probably in the same industry or based on geographical region. But all of these four forms of cloud computing provide the services at one or four levels. These four levels are defined as application level, platform level, infrastructure level, or business process level.
Figure 2.
Service model of cloud computing
Over the time, the concept of cloud computing has been changed and new term has evolved “Everything as a Service” (XaaS) such as the applications, infrastructure, processes can be obtained from the cloud. National Institute of standard technology (NIST) defines cloud computing as follows: “Cloud Computing is a model for enabling convenient, on-demand network access to a share pool of configurable computing resources (i.e. Networks, Servers, Storage, Applications and Services) that can be rapidly provisioned and released with minimal management effort or service provider interaction”. NIST has derived five essential characteristics or benefits of cloud computing that neither can be provided by simple web server nor virtualized data centres. These are:
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On-Demand Self-Service: Users can make use of cloud at any time anywhere.
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Resource Pooling: Customers share pool of computing resources and data storage. Cloud customers might know where to store data at a macro level but they do not know the exact location of the application and data storage
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Broad Network Access: All the smart devices having internet connectivity such as Laptops, Mobile phones, iPads and other devices may access the service using clients as the web browsers.
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Rapid Elasticity: The storage capacity, network bandwidth, computing capacity is so flexible that it can be increased or reduced at instance and provides an optimal solution for the resource usage.
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Measured Device: Cloud system allows the resources to be used and at the same time it can monitor, control, and report usage in a transparent way.