3.5.2. Migration

In addition to normal service operations, virtual machines support one behavior not supported by other services: migration. Migration minimizes downtime of virtual machines by removing the requirement for a start/stop in order to change the location of a virtual machine within a cluster.
There are two types of migration supported by rgmanager which are selected on a per-VM basis by the migrate attribute:
  • live (default) — the virtual machine continues to run while most of its memory contents are copied to the destination host. This minimizes the inaccessibility of the VM (typically well under 1 second) at the expense of performance of the VM during the migration and total amount of time it takes for the migration to complete.
  • pause - the virtual machine is frozen in memory while its memory contents are copied to the destination host. This minimizes the amount of time it takes for a virtual machine migration to complete.
Which migration style you use is dependent on availability and performance requirements. For example, a live migration may mean 29 seconds of degraded performance and 1 second of complete unavailability while a pause migration may mean 8 seconds of complete unavailability and no otherwise degraded performance.

Important

A virtual machine may be a component of service, but doing this disables all forms of migration and most of the below convenience features.
Additionally, the use of migration with KVM requires careful configuration of ssh.