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The Infrastructure as a Service (IaaS) model lets you create VMs and virtual networks in the cloud according to your desired specifications regarding processing power, memory, storage, and networking. The IaaS model is probably the easiest to understand because it most closely mirrors the virtualized server environments in modern data centers. NIST describes it as follows:

The capability provided to the consumer is to provision processing, storage, networks, and other fundamental computing resources where the consumer is able to deploy and run arbitrary software, which can include operating systems and applications. The consumer does not manage or control the underlying cloud infrastructure but has control over operating systems, storage, deployed applications; and possibly limited control of select networking components (e.g., host firewalls).

IaaS is really just a server and network virtualization environment offered as a service. Because of this, it offers the customer the most flexibility of any of the e-service models. You can provision to your specifications any number of VMs, on which you can run the software of your choice. Also, some IaaS offerings even allow you to choose the virtualized host on which your VMs run, giving you the ability to spread VMs across multiple hosts for resiliency.

IaaS (shown in Figure 1.8) allows the company's data center equipment to be replaced by the cloud equivalent but retains the ability to build software infrastructure on top of the hardware as can be done in a private data center.

FIGURE 1.8 IaaS