Service models in Cloud Computing

Introduction

Categories of service model

1) Software-as-a-Service (SaaS)

• SaaS is known as 'On-Demand Software'.
• It is a software distribution model. In this model, the applications are hosted by a cloud service provider and publicized to the customers over internet.
• In SaaS, associated data and software are hosted centrally on the cloud server.
• User can access SaaS by using a thin client through a web browser.
• CRM, Office Suite, Email, games, etc. are the software applications which are provided as a service through Internet.
• The companies like Google, Microsoft provide their applications as a service to the end users.

• SaaS is easy to buy because the pricing of SaaS is based on monthly or annual fee and it allows the organizations to access business functionalities at a small cost, which is less than licensed applications.
• SaaS needed less hardware, because the software is hosted remotely, hence organizations do not need to invest in additional hardware.
• Less maintenance cost is required for SaaS and do not require special software or hardware versions.

• SaaS applications are totally dependent on Internet connection. They are not usable without Internet connection.
• It is difficult to switch amongst the SaaS vendors.

2) Platform-as-a-Service (PaaS)

• PaaS is a programming platform for developers. This platform is generated for the programmers to create, test, run and manage the applications.
• A developer can easily write the application and deploy it directly into PaaS layer.
• PaaS gives the runtime environment for application development and deployment tools.
• Google Apps Engine(GAE), Windows Azure, SalesForce.com are the examples of PaaS.

• PaaS is easier to develop. Developer can concentrate on the development and innovation without worrying about the infrastructure.
• In PaaS, developer only requires a PC and an Internet connection to start building applications.

• One developer can write the applications as per the platform provided by PaaS vendor hence the moving the application to another PaaS vendor is a problem.

3) Infrastructure-as-a-Service (IaaS)

• IaaS is a way to deliver a cloud computing infrastructure like server, storage, network and operating system.
• The customers can access these resources over cloud computing platform i.e Internet as an on-demand service.
• In IaaS, you buy complete resources rather than purchasing server, software, datacenter space or network equipment.
• IaaS was earlier called as Hardware as a Service(HaaS). It is a Cloud computing platform based model.
• HaaS differs from IaaS in the way that users have the bare hardware on which they can deploy their own infrastructure using most appropriate software.

• In IaaS, user can dynamically choose a CPU, memory storage configuration according to need.
• Users can easily access the vast computing power available on IaaS Cloud platform.

• IaaS cloud computing platform model is dependent on availability of Internet and virtualization services.