Host aggregates allow us to logically group hardware and create partitions in our deployment. Host aggregates are often used to group same specification hardware together, such as Compute hosts that have a certain type of hardware such as SSDs available. We can then define extra pieces of information associated with that grouping of hardware (known as metadata), which is exposed to a user when launching instances. For example, we can launch an instance and specify that we want it to run on compute hosts that have SSDs. By supplying this extra information, the compute hosts that understand this metadata will request that the instance be launched on that hardware.

Compute hosts can also belong to more than one host aggregate. This allows for greater flexibility when defining the partitions by allowing compute hosts to be organized in multiple ways. The following diagram shows an example of using host aggregate to define groups of Compute resource. Only an administrator...