Cloud Computing: Service Model of Cloud Computing

What are the Service Model in Cloud Computing?

Service delivery in Cloud Computing comprises three different service models, namely Infrastructure-as-a-Service (IaaS), Platform-as-a-Service (PaaS), and Software-as-a-Service (SaaS). The three service models or layer are completed by an end user layer that encapsulates the end user perspective on cloud services.

If a cloud user accesses services on the infrastructure layer, for instance, he can run his own applications on the resources of a cloud infrastructure and remain responsible for the support, maintenance, and security of these applications himself. If he accesses a service on the application layer, these tasks are normally taken care of by the cloud service provider.

1. Software as Service (SaaS):- Software-as-a-Service provides complete applications to a cloud’s end user. It is mainly accessed through a web portal and service oriented architectures based on web service technologies. Credit card or bank account details must be provided to enable the fees for the use of the services to be billed.
The services on the application layer can be seen as an extension of the ASP (application service provider) model, in which an application is run, maintained, and supported by a service vendor. The main differences between the services on the application layer and the classic ASP model are the encapsulation of the application as a service, the dynamic procurement, and billing by units of consumption (pay as you go). However, both models pursue the goal of focusing on core competencies by outsourcing applications.

                   

2. Platform as a Service:- PaaS comprises the environment for developing and provisioning cloud applications. The principal users of this layer are developers seeking to develop and run a cloud application for a particular platform. They are supported by the platform operators with an open or proprietary language, a set of essential basic services to facilitate communication, monitoring, or service billing, and various other components, for instance to facilitate startup or ensure an application’s scalability and/or elasticity (see figure 3). Distributing the application to the underlying infrastructure is normally the responsibility of the cloud platform operator. The services offered on a cloud platform tend to represent a compromise between complexity and flexibility that allows applications to be implemented quickly and loaded in the cloud without much configuration. Restrictions regarding the programming languages supported, the programming model, the ability to access resources, and persistency are possible downsides.

The services on the infrastructure layer are used to access essential IT resources that are combined under the heading Infrastructure-as-a-Service (IaaS). These essential IT resources include services linked to computing resources, data storage resources, and the communications channel. They enable existing applications to be provisioned on cloud resources and new services implemented on the higher layers.
Physical resources are abstracted by virtualization, which means they can then be shared by several operating systems and end user environments on the virtual resources – ideally, without any mutual interference. These virtualized resources usually comprise CPU and RAM, data storage resources (elastic block store and databases), and network resources as displayed below.

Infrastructure-as-a-Service (IaaS) Stack

August 07, 2013