Migrate instances¶

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 Configure SSH between compute nodes.

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

   $ openstack server list
   

2. Use the openstack server migrate command.

   $ openstack server migrate --live TARGET_HOST 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
   
   # Migrate the VM to an alternate hypervisor
   echo -n "Migrating instance to alternate host"
   VM_ID=$1
   openstack server migrate $VM_ID
   VM_OUTPUT=$(openstack server show $VM_ID)
   VM_STATUS=$(echo "$VM_OUTPUT" | grep status | awk '{print $4}')
   while [[ "$VM_STATUS" != "VERIFY_RESIZE" ]]; do
   echo -n "."
   sleep 2
   VM_OUTPUT=$(openstack server show $VM_ID)
   VM_STATUS=$(echo "$VM_OUTPUT" | grep status | awk '{print $4}')
   done
   nova resize-confirm $VM_ID
   echo " instance migrated and resized."
   echo;
   
   # Show the details for the VM
   echo "Updated instance details:"
   openstack server show $VM_ID
   
   # Pause to allow users to examine VM details
   read -p "Pausing, press <enter> to exit."
   

ERROR (Forbidden): Policy doesn't allow compute_extension:admin_actions:migrate to be performed. (HTTP 403)``

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.