Introduction to Cloud Computing

Cloud computing refers to applications and services that run on a distributed network using virtualized resources and are accessed by common and standard networking protocols.

Cloud computing is built on two essential concepts: (i) abstraction and (ii) virtualization.

• Abstraction: It hides details of system implementation from users and developers. The location of the physical systems, where applications are running and data is stored, is unknown.
• Virtualization: Cloud computing virtualizes systems by pooling and sharing resources. Resources are provisioned based on the user's requirement and costs are assessed on the pay-per-use model.

Cloud computing is an abstraction based on the notion of pooling physical resources and presenting them as virtual resources.

---

Cloud Computing Service Models

Different cloud service providers provide services in different forms.

• Infrastructure as a Service: With the blessings of virtualization technology, users can access and manage virtual resources, like virtual machines having full control like a physical machine/host. Users can access virtual machines, where they can install Software according to their needs. But they do not have control to manage the physical resources of the physical machines on which virtual machines are running.

Examples: Amazon Elastic Compute Cloud (EC2), GoGrid, etc.

• Platform as a Service: It provides the capability to the users to deploy their applications in cloud infrastructure. The users cannot manage or control the underlying cloud infrastructure like network, servers, operating systems, or storage, but has full control over the deployed applications. 

Examples: GoogleAppEngine, RightScale, Salesforce.com etc.

• Software as a Service: It provides the capability to the users to use the provider's applications running on their cloud infrastructure. The users cannot manage or control the underlying cloud infrastructure, but they can configure the user-specific settings of the application.

Examples: GoogleDocs, SalesForce services etc.