12.3. Automatic Virtual Machine Migration

Red Hat Enterprise Virtualization Manager is able to automatically live migrate virtual machines. The Manager automatically initiates live migration of virtual machines when a host is being moved into maintenance mode. Where this occurs live migration of all virtual machines running on the host is attempted. The destination host for each virtual machine will be assessed as that virtual machine is migrated, so as to spread the additional load across the cluster.
The Manager will also automatically initiate live migration of virtual machines in order to maintain load balancing or power saving levels in the cluster to be in line with cluster policy, if it has been defined. While by default no cluster policy is defined it is recommended that administrators specify the cluster policy which best suits the needs of their environment. Administrators can also disable automatic, or even manual, live migration of specific virtual machines where required.

12.3.1. Moving a Host to Maintenance Mode

Many common maintenance tasks, including network configuration and deployment of software updates, require that virtualization hosts be placed into maintenance mode. When a host is placed into maintenance mode the Red Hat Enterprise Virtualization Manager attempts to migrate all running virtual machines to alternative hosts. The normal prerequisites for live migration apply.
In particular there must be at least one active host in the cluster with capacity to run the virtual machine(s) being migrated as a result of the host being placed into maintenance mode. To move a host to maintenance mode follow these steps:
  1. Ensure the Tree tab is selected in the left hand pane of the Administration Portal.
  2. Expand the tree view using the + buttons until the host to be moved into maintenance mode is visible.
  3. Select the host to be moved into maintenance mode. Click the Maintenance button.
    All running virtual machines will be migrated to alternative hosts. Once this has occurred the host is moved into maintenance mode. The Status field of the host will change to Preparing for Maintenance, and finally Maintenance when the operation completes successfully.
  4. Result:
    All running virtual machines have been migrated to alternatives hosts. The host has been placed into maintenance mode.