The US
National Institute of Standards and Technology (NIST) defines infrastructure as a service as: IaaS clouds often offer additional resources such as a virtual-machine
disk-image library, raw
block storage, file or
object storage, firewalls, load balancers, IP addresses,
virtual local area networks (VLANs), and software bundles. IaaS-cloud providers supply resources on-demand from the large pools of equipment installed in
data centers. For
wide-area connectivity, customers can use either the Internet or
carrier clouds (dedicated
virtual private networks, VPNs). To deploy their applications, users install operating-system images and the application software on the cloud infrastructure. Users patch and maintain the operating systems. IaaS services are typically billed as a utility: cost reflects the amount of resources allocated or consumed. Typically, IaaS involves the use of a
cloud orchestration technology such as
OpenStack,
Apache CloudStack, or
OpenNebula. It manages the creation of a virtual machine (VM) and decides on the hypervisor (i.e. physical host) in order to start it. A
hypervisor runs
virtual machines (VMs) as guests. Pools of hypervisors in the cloud operational system can support large numbers of virtual machines and the ability to scale services up and down according to demand by customers. Hypervisors include
Xen,
Oracle VirtualBox,
Oracle VM,
KVM,
VMware ESX/ESXi, or Microsoft
Hyper-V. It also enables VM migration between hosts, allocates storage volumes, and attaches them to VMs that track usage information for billing. An alternative to hypervisors is Linux
containers, which run in isolated partitions of a
Linux kernel that runs directly on the physical hardware. Containers are isolated, secured and managed using Linux
cgroups and namespaces. Containerisation offers higher performance than virtualization because there is no hypervisor overhead. == Economic impact ==