[Cloud] Cloud Computing Definition

Since the term cloud computing is a relatively new term compared to other technologies in the IT field, different people/organizations have come up with different definitions. Out of all of them, in my opinion, NIST definition is by far the best in terms of clarity and completeness.

NIST definition of cloud computing is quite simple and upto the point:

• Essential characteristics
• On-demand self-service - provisioning of computing capabilities without any human intervention
• Broad network access - capabilities are available over the network/any device
• Resource pooling - multi-tenant model to serve multiple customers from pooled resources
• Rapid elasticity - capabilities can be elastically provisioned or released based on demand
• Measured service - resource usage can be monitored to provide metering capability
• Service models
• Software as a Service - consumers have access to applications running on provider's cloud - zero software installation; e.g. Salesforce, Oracle CRM
• Platform as a Service - consumers have control over deployed apps - consumers are provided middleware running in provider's cloud
• Infrastructure as a Service - consumers have control over OS, storage and deployed apps - consumers are provided virtual machines

The following diagram illustrate the above three service models:

(Source: Wikipedia)

• Deployment models
• Private cloud - provisioned for exclusively used by one organization
• Community cloud - provisioned for used by one community with similar interest
• Public cloud - provisioned for open use by general public - e.g. Amazon cloud service
• Hybrid cloud - any combination of the above three

The following diagram from Microsoft provide some more information on the deployment models:

(Source: Microsoft.com)