5.1. Load Balancing, Scheduling, and Migration
Individual hosts have finite hardware resources, and are susceptible to failure. To mitigate against failure and resource exhaustion, hosts are grouped into clusters, which are essentially a grouping of shared resources. A Red Hat Virtualization environment responds to changes in demand for host resources using load balancing policy, scheduling, and migration. The Manager is able to ensure that no single host in a cluster is responsible for all of the virtual machines in that cluster. Conversely, the Manager is able to recognize an underutilized host, and migrate all virtual machines off of it, allowing an administrator to shut down that host to save power.
The Manager responds to changes in available resources by using the load balancing policy for a cluster to schedule the migration of virtual machines from one host in a cluster to another. The relationship between load balancing policy, scheduling, and virtual machine migration are discussed in the following sections.