Cloud Computing Characteristics
The cloud computing characteristics define the requirements for a data center to offer cloud services. The NIST came up with five essential characteristics for the cloud computing:
- On-demand self-service
- Broad network access
- Resource pooling
- Rapid elasticity
- Measured service
All five essential characteristics are important, and they separate the cloud services offering from a hosting or colocation service.
On-Demand Self-Service
The NIST defines on-demand self-service as follows (see Figure 21-2):

Figure 21-2 On-Demand Self-Service Essential Characteristic
“A consumer can unilaterally provision computing capabilities, such as server time and network storage, as needed automatically without requiring human interaction with each service provider.”
This definition immediately sets a requirement for the data center to have the needed level of automation and orchestration, which will allow the user to access the cloud portal and select a service and provision it, without waiting for administrators from the provider to set it up. A simple example is how a user can open Outlook.com or Gmail.com and select an offered service, such as registering and creating a personal email account. Then, without waiting for any interaction with an employee from the provider, the account will be created and available almost immediately.
Measured Service
When the services are used, it is important for both the service provider and the user to know what was consumed and how it was consumed, what resources were utilized, and how the consumption changes in time (see Figure 21-3). This also applies to the access bandwidth and the quantity of data transported. This is important because the charges are calculated based on what was consumed and for how long. It is also important for the end user, as they can downsize or upsize the resources they use, based on the cost, the need for resources, and so on. Another aspect is that service providers can analyze the data for consumption and trends in order to plan for expanding the capacities of their data centers, as the ability to scale is important for the needs of the customers.

Figure 21-3 Measured Services Essential Characteristic