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5.9. Evacuating an instance

If you want to move an instance from a dead or shut-down Compute node to a new host in the same environment, you can evacuate it. The evacuate process rebuilds the instance on another Compute node. If the instance uses shared storage, the instance root disk is not rebuilt during the evacuate process, as the disk remains accessible by the destination Compute node. If the instance does not use shared storage, then the instance root disk is also rebuilt on the destination Compute node.

注記
  • You can only perform an evacuation when the Compute node is fenced, and the API reports that the state of the Compute node is "down" or "forced-down". If the Compute node is not reported as "down" or "forced-down", the evacuate command fails.
  • To perform an evacuation, you must be a cloud administrator.
  • During evacuations, the Compute service rebuilds the evacuated instances from scratch, and adjusts the machine type to the machine type of the destination Compute node. Therefore, if you evacuate an instance with a RHEL-7.5 machine type running on a RHEL-7.5 Compute node, to a RHEL-7.6 Compute node, the migrated instance on the destination Compute node will have a RHEL-7.6 machine type.

5.9.1. Evacuating one instance

You can evacuate instances one at a time.

Procedure

  1. Log onto the failed Compute node as an administrator.
  2. Disable the Compute node:

    (overcloud)[stack@director ~]$ openstack compute service set \
    <host> <service> --disable
    • Replace <host> with the name of the Compute node to evacuate the instance from.
    • Replace <service> with the name of the service to disable, for example nova-compute.
  3. To evacuate an instance, run the following command:

    (overcloud)[stack@director ~]$ nova evacuate [--password <pass>] <vm> [dest]
    • Replace <pass> with the admin password to set for the evacuated instance. If a password is not specified, a random password is generated and output when the evacuation is complete.
    • Replace <vm> with the name or ID of the instance to evacuate.
    • Replace [dest] with the name of the Compute node to evacuate the instance to. If you do not specify the destination Compute node, the Compute scheduler selects one for you. You can find possible Compute nodes by using the following command:

      (overcloud)[stack@director ~]$ openstack hypervisor list