nova/doc/source/admin/migration.rst

Migrate instances

Note

This documentation is about cold-migration. For live-migration usage, see live-migration-usage.

When you want to move an instance from one compute host to another, you can use the openstack server migrate command. The scheduler chooses the destination compute host based on its settings. This process does not assume that the instance has shared storage available on the target host. If you are using SSH tunneling, you must ensure that each node is configured with SSH key authentication so that the Compute service can use SSH to move disks to other nodes. For more information, see cli-os-migrate-cfg-ssh.

1. To list the VMs you want to migrate, run:

   $ openstack server list

2. Use the openstack server migrate command.

   $ openstack server migrate VM_INSTANCE

3. To migrate an instance and watch the status, use this example script:

   #!/bin/bash
   
   # Provide usage
   usage() {
       echo "Usage: $0 VM_ID"
       exit 1
   }
   
   [[ $# -eq 0 ]] && usage
   VM_ID=$1
   
   # Show the details for the VM
   echo "Instance details:"
   openstack server show ${VM_ID}
   
   # Migrate the VM to an alternate hypervisor
   echo -n "Migrating instance to alternate host "
   openstack server migrate ${VM_ID}
   while [[ "$(openstack server show ${VM_ID} -f value -c status)" != "VERIFY_RESIZE" ]]; do
       echo -n "."
       sleep 2
   done
   openstack server resize --confirm ${VM_ID}
   echo " instance migrated and resized."
   
   # Show the details for the migrated VM
   echo "Migrated instance details:"
   openstack server show ${VM_ID}
   
   # Pause to allow users to examine VM details
   read -p "Pausing, press <enter> to exit."

Note

If you see the following error, it means you are either running the command with the wrong credentials, such as a non-admin user, or the policy.json file prevents migration for your user:

Policy doesn't allow os_compute_api:os-migrate-server:migrate to be performed. (HTTP 403)

Note

If you see the following error, similar to this message, SSH tunneling was not set up between the compute nodes:

ProcessExecutionError: Unexpected error while running command.
Stderr: u Host key verification failed.\r\n

The instance is booted from a new host, but preserves its configuration including instance ID, name, IP address, any metadata, and other properties.