✓ In contrast,  private services  are provided inside a company’s firewall, enabling IT management to provide  a self-service portal for employees and partners to easily  access approved services. Characteristics of both models are covered in this section. When you purchase server and storage resources using IaaS  services, you gain immediate access to the resources you  need. You aren’t, however, renting the actual servers or other  infrastructure. It’s not like a rental truck pulls up to your  office to deliver the services. The physical components stay  put in the infrastructure service provider’s data center. Within a private IaaS, renting takes on a different focus.  Although you may not charge each user to access a resource,  in the charge-back model, you can allocate usage fees to an  individual department based on usage over a week, month, or year. Because of the flexibility of the IaaS model, the heaviest resource users can pay more than those who use  fewer resources. Self-service provisioning  is a key characteristic of IaaS that  enables the user to obtain resources — such as servers and  networking — through a self-service portal without relying on  IT to provision these resources for them. The portal is similar  to a banking ATM model that handles repetitive tasks easily  through a self-service interface. Dynamic scaling  occurs when resources can be automatically  expanded or contracted based on the requirements of the  workload or task. If users need more resources than expected,  they can get them immediately. A provider or creator of IaaS  typically optimizes the environment so the hardware, the  operating system, and automation can support a huge number  of workloads. Many consumers acquire capacity based on an on-demand  model with no contract. In other situations, the consumer  signs a contract for a specific amount of storage and/or These materials are the copyright of John Wiley & Sons, Inc. and any  dissemination, distribution, or unauthorized use is strictly prohibited. Service levels Dynamic scaling Self-service provisioning Renting  Chapter 2: Digging Deeper into IaaS and PaaS 17