openstack-manuals/doc/user-guide-admin/source/cli_nova_migrate.rst

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.

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

   $ nova list

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

   $ nova show VM_ID

3. Now, use the nova migrate command:

   $ nova migrate VM_ID

4. To migrate of 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
   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.