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)
