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Chapter 3. Cloud Infrastructure Concepts
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3.4. About Clusters
A cluster provides a way to group hosts. To be precise, a cluster is a XenServer server pool, a set
of KVM servers, a set of OVM hosts, or a VMware cluster preconfigured in vCenter. The hosts in a
cluster all have identical hardware, run the same hypervisor, are on the same subnet, and access the
same shared primary storage. Virtual machine instances (VMs) can be live-migrated from one host to
another within the same cluster without interrupting service to the user.
A cluster is the fourth-largest organizational unit within a CloudPlatform deployment. Clusters
are contained within pods, pods are contained within zones, and zones can be contained within
regions. Size of the cluster is only limited by the underlying hypervisor, although the CloudPlatform
recommends you stay below the theoretically allowed maximum cluster size in most cases.
A cluster consists of one or more hosts and one or more primary storage servers.
Even when local storage is used, clusters are still required. In this case, there is just one host per
cluster.
(VMware) If you use VMware hypervisor hosts in your CloudPlatform deployment, each VMware
cluster is managed by a vCenter server. The CloudPlatform administrator must register the vCenter