National Institute of Standards and Technology (NIST) is an agency under the scope of US Department of Commerce. NIST is responsible for defining standards in Science and Technology.

The Computer Security Division of NIST has provided a formal Definition and Characteristics of Cloud computing.

NIST five essential characteristics of Cloud Computing

On demand self-service
Broad network access
Resource pooling
Rapid Elasticity
Measured service

ISO 17788 six essential characteristics of Cloud Computing

On demand self-service
Broad network access
Resource pooling
Rapid Elasticity
Measured service
Multi-tenancy

1. On Demand Self service

Computer services such as Email, Application Network, or Server service can be provided without requiring interaction with each service provider.

Self-service means that the consumer performs all the actions needed to acquire the service himself, instead of going through an IT department. For example – The consumer’s request is then automatically processed by the cloud infrastructure, without human intervention on the provider’s side.

2. Broad Network Access

Cloud capabilities are available over the network and accessed through standard mechanism that promote use by heterogeneous client such as mobile phone, laptop

3. Resource pooling

– The providers computing resources are pooled together to serve multiple customers, with different physical and virtual resources dynamically assigned and reassigned according to the customers demand.
– There is a sense of location independence in that the customer generally has no control or knowledge over the exact location of the provided resources but may be able to specify lication at a higher level of abstraction (e.g. contry, state, or datacenter).
– Example of resources include storage, processing, memory, and network bandwidth.

4. Rapid elasticity

– Capabilities can be elastically provisioned and released, in some cases automatically, to scale rapidly outward and inward commensurate with demand.
– To the consumer, the capabilities available for provisioning often appear to be unlimited and can be appropriated in any quantity at any time.

5. Measured service

– Cloud systems automatically control and optimize resource use by leveraging a metering capability at some level of abstraction appropriate to the type of service (e.g. storage, processing, bandwidth, and active use account).
– Resource usage can be monitored, controlled, and reported, providing transparency for both the provider and consumer of the utilized service.

6. Multi-tenancy

In a private cloud, the customers are also called tenants, can have different business divisions inside the same company. In a public cloud, the customers are often entirely different organizations.

Most public cloud providers use the multi-tenancy model. Multi-tenancy allows customers to run one server instance, which is less expensive and makes it easier to deploy updates to a large number of customers.