.. highlight: bash
   :linenothreshold: 5

===============================================
Migrate single instance to another compute host
===============================================

When you want to move an instance from one compute host to another,
you can use the ``nova 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.

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

   $ nova list

#. After selecting a VM from the list, run this command where :guilabel:`VM_ID`
   is set to the ID in the list returned in the previous step::

   $ nova show VM_ID

#. Now, use the ``nova migrate`` command::

   $ nova migrate VM_ID

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

   .. code-block:: bash
     :linenos:

     #!/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
     nova migrate $VM_ID
     VM_OUTPUT=`nova 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=`nova 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:"
     nova show $VM_ID

     # Pause to allow users to examine VM details
     read -p "Pausing, press <enter> to exit."

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

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

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