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Top1. Introduction
From the past decades, internet demands are increasing exponentially. Users access the internet to store and retrieve their data. Apart from data storage, users require different services on demand basis with better quality of service. Cloud Computing concept is developed in which cloud acts as a metaphor for the internet (Hwang et al., 2013) and computing acts as utilizing the internet technology to complete the task. It offers services such as server, storage and application on requirement basis. Cloud offers three types of services such as SaaS, PaaS, IaaS. In SaaS, on demand basis cloud provider provides their services to the end user. Similarly, in PaaS the users get the liberty to develop its own application, because it offers different computing platforms like operating system, web server, database, programming language. IaaS provider provides infrastructure and resources in a virtualized manner (Zhang et al., 2010). The cloud consists of three major components that is end users, broker and cloud provider. Here the end user request for the services, after getting the request broker, who acts as an interface between end user and cloud provider negotiate with different cloud vendors by considering the need of end user. Recently the IT industries are focusing to enhance the quality of service in cloud computing by optimizing the time and cost in various measures due to the flexible cloud architecture.
Cloud computing architecture consists of four layers. The inner layer is the hardware layer; next to the inner layer is the infrastructure layer. Platform layer is above the infrastructure layer and application layer is the outermost layer. The characteristics of each layer are as flows:
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Hardware Layer: This layer handles the physical resources of the cloud, including physical servers, routers, switches, power, and cooling systems. In practice, the hardware layer is typically implemented in data centers. A data center usually contains thousands of servers that are organized in racks and interconnected through switches and routers. Hardware configuration, fault tolerance, traffic management, and power management are typical the issues in the hardware layer.
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Infrastructure Layer: The infrastructure layer is an essential component of cloud architecture. It is also known as the virtualization layer. This layer creates a pool of storage and computing resources by using virtualization technologies such as Xen, Kernel-based Virtual Machine (KVM), and VMware. They are helpful in dynamic resource assignment in a cloud system.
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Platform Layer: This layer is on the top of the infrastructure layer. It consists of operating systems and application frameworks. The purpose of the platform layer is to minimize the burden of deploying applications directly into VM containers. For example, Google App Engine runs on the platform layer to provide application programming interface (API) support for implementing storage, database, and business logic of typical web applications.
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Application Layer: Cloud application layer is different from traditional applications, and it can leverage the automatic-scaling feature to achieve better performance, availability, at a lower operating cost. Each layer is loosely coupled with the layers above and below, allowing each layer to evolve separately. The architectural modularity allows cloud computing to support a broad range of application requirements while reducing management and maintenance overhead.
Although cloud computing is the mega trend in recent days, still the issues in this computing paradigm include automated service provisioning, resource management, task scheduling, Virtual Machine Migration, Server Management, Privacy and Security etc.