Cloud Computing Overview
Cloud computing has become a new computing paradigm as it can offer dynamic IT infrastructure, configurable service and QoS guaranteed computing environment (Wang et al., 2008). Cloud computing can be illustrated from the following aspects:
SPI model - Cloud computing originates from the concept “Hardware as a Service” (HaaS), “Software as a Service” (SaaS). Cloud now advances from SaaS to “Platform as a Service” (PaaS) and “Infrastructure as a Service” (IaaS), known as SPI1 model. In Cloud computing, customers can avoid capital expenditure on hardware and software by renting the usage from service provider of third party, rather than owning the physical infrastructure by themselves. The hardware and software are rendered to customers as IT services.
Scalability / elasticity - Klems and Gaw (in Geelan, 2008) claim that automatic scale of infrastructure for load balancing is a key element in Cloud computing. The delivered services can elastically / dynamically grow its capacity on an as-needed basis so that the Quality of Service (QoS) can be guaranteed: “on-demand services are all cloud computing based” (de Haaff, 2008).
“Pay-per-use” / “Pay-as-you-go” / “Utility computing” - There is also a vision that Cloud computing is more like a business revolution, rather than a technology evolution. Business model, or we call “pay-per-use”, “pay-as-you-go”, and ”utility computing” is another feature of Cloud computing (Geelan, 2008; Watson, Lord, Gibson et al., 2008); Buyya, Yeo, Venugopal, 2009; McFedries, 2008). The usage of the resource will be metered and service customers will pay bill to service provider for the actual resource usage.
Data centre - Another view of Cloud presents the data centre as the basic unit of the Cloud infrastructure (Vaquero, Rodero-Merino, Caceres and Lindner, 2009). Data centre can offer huge amount of computing power and data storage. The capacity of the data centre can change dynamically when handling a task. According to Vaquero, Rodero-Merino, Caceres and Lindner (2009), this is associated with the concept “massive data scalability” proposed by Hand (2007).
Virtualisation - Cloud computing can also be regarded as a “virtualised hardware and software” (Sheynkman in Geelan, 2008). This perspective emphasizes the use of virtualisation technology in the Cloud computing. Virtualization technologies multiplex hardware and have made the flexible and scalable provision of resource as hardware and software on demand easier. Virtual machine techniques, such as VMware (http://www.xen.org), offer virtualized IT-infrastructures on demand. Virtual network advances, such as Virtual Private Network (VPN), support users with a customized network environment to access Cloud resources.