In some cases, OpenStack users require their virtual machine instances to run with a specific underlying hardware or hypervisor characteristics, for example, to guarantee certain behavior like disk or CPU performance. Nova the grouping of hypervisor hosts with specific characteristics into hypervisor host aggregates. Nova host aggregates are nova-compute nodes grouped by a certain characteristics they share; flavors can be restricted to be launched on host aggregates featuring matched characteristics.
Nova host aggregates allow to partition compute hypervisors into logical groups, for example, the partitioning of hosts by common infrastructure, such as shared storage devices, hosts sharing a similar CPU, trusted compute hardware, or other types of hardware. This is preferred mostly to ensure consistent performance when launching instances of certain flavors. Another common use of host aggregates is categorizing hosts by class of service, such as Gold and Silver...