compute. A typical IaaS contract has some level of service guarantee. At the low end, a provider may state that the company will do its best to provide good service. Depending on the service and the price, you may contract for 99.999 percent availability. The level of service you require depends on the workloads you’re running. We talk more about service levels in Chapter 5. 

## Licensing 

The use of public IaaS has led to innovations in licensing and payment models for software you want to run in your cloud environment (not the license between you and your cloud provider). For example, some IaaS and software providers have created the Bring Your Own License (BYOL) plan so you have a way to use your software in both traditional or cloud environments. Another option is Pay As You Go (PAYG), which generally integrates the software licenses with the on-demand infrastructure services. 

## Metering 

Metering ensures that users are charged for the resources they request and use. This metering to assess the charges for the IaaS services begins when the instance is initiated and ends when the instance is terminated. In addition to the basic per-instance charge, the IaaS provider may include charges for storage, data transfer, and optional services like enhanced security, support, or advanced monitoring. 

## Considering a private IaaS 

A company would choose a private IaaS over a public one for three compelling reasons: 

✓ The company needs to control access because of security concerns. 

✓ The company may require that business critical applications demonstrate predictable performance while minimizing risk. 

✓ The company sees itself as a service provider to its customers and partners. 

