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Cloud computing is visualized as the next-generation prototype. Cloud computing provides applications and computing resources (software and hardware) dynamically over the internet as services to its clients. Cloud computing has become a promising and efficient computing model and engrossed extensive attention and support in several fields. Moreover, cloud computing environment provides many services such as application hosting, service outsourcing and resource renting which demonstrates the core perception of an on-demand service in the IT field. National Institute of Standards and Technology (NIST) (Mell & Grance, 2011) defined cloud computing as “cloud computing permits universal, expedient, and on-demand network access to a shared pool of configurable computing resources that can be quickly indulged and released with minimum effort.” The cloud service provider provides three types of services which are shown in figure 1.
Figure 1. Cloud computing service model
Figure 1 shows cloud services which are categorized as 1) Software as a Service (SaaS): It provides access to web applications (File storage, email, social networking, etc.) running on their web servers. Examples of such kind of cloud providers are Zoho, Salesforce.com and Google Apps. 2) Platform as a Service (PaaS): It provides an environment where users can run their applications without worrying about managing the hardware, tools, network storage as they all are managed by the cloud service provider. The Google APP Engine, Windows Azure are examples of these service providers. Google App Engine, Aptana cloud.3) Cloud Infrastructure as a Service (IaaS): It provides raw computing storage space and power and user can also manage the intrinsic virtual machines as well as network, storage space and operating system. Dropbox, Mozy, Akamai, AmazonEC2 and Rack space cloud service providers come in this category. The basic structure of cloud computing is shown in figure 2.
Figure 2. A generic architecture of cloud computing
Figure 2 illustrates the basic architecture of cloud computing. The cloud can be divided on the basis of scope, access, ownership and availability such as 1) Private cloud is mainly operated by enterprises and is used inside only or access from outside, but is not accessible by non-company members. 2) Community cloud can be accessed only by a specific community of consumers from different organizations which have shared concerns. 3) Public cloud: Anyone can open and access. Further, open means not free and many cloud service providers charge users for their services 4) Hybrid cloud: It is a composition of two or more different cloud infrastructures like public and private. The cloud is an environment of the hardware and software resources that present various services over the network or the Internet to persuade user’s specification’s (Leavitt, 2009).