Bootstrap your QCOW Images for the Rackspace Public Cloud

In the world of Cloud Computing, hypervisors and disk image formats come in various shapes & sizes and are by no means made equal. In the Rackspace Public Cloud, we utilize Citrix XenServer as our hypervisor, which requires that our disk images be in the VHD format.

However, it is very common for folks who utilize the popular KVM hypervisor to want to leverage an existing, custom QCOW image when working with our Public Cloud.

To minimize the redundancy of recreating duplicate images, it would be beneficial to be able take an existing or new QCOW image and modify it to operate on our Public Cloud. This would immensely cut down the maintenance of base images customers create that they wish to share across multiple cloud infrastructures.

In this tutorial, I will walk you through the following steps:

  • Pull a vanilla UEC version of an Ubuntu 14.04 QCOW image
  • Modify the OS to work with the Rackspace Public Cloud
  • Convert it to the required VHD format XenServer expects
  • Upload the image to Cloud Files for registration with Cloud Images
  • Utilize Cloud Images to register the image for future instantiation


  • This in an unofficial tutorial, so the conversion is not guaranteed to fully function in the entirety of the Rackspace Public Cloud platform
  • Converted OS’s other than Ubuntu 14.04 have not been thorougly tested with this tutorial. Therefore, it is recommended you too use Ubuntu 14.04

Assumptions & Recommendations

  • An existing Public Cloud account
  • python-novaclient is installed
  • pyrax is installed
    • Note: Public Cloud pyrax credentials are expected to be stored in ~/pyrax_rc, formatted as such:
username = <RAX_USERNAME>
api_key = <RAX_API_KEY>
  • At least an Ubuntu 12.04 bare-metal machine is recommended to perform the conversion, as issues rose with QCOW image mounting in certain virtualized environments

How-To Steps

0. Preamble

For the sake of not showing lengthy code-blocks, all the scripts referred to below are located in a Github repo

It is recommended you clone and operate out of this repo:

git clone
cd rpc_rd/qcow_image/

1. Compile Xen tool ‘vhd-util’

  • Pulls Xen 4.4.0 source and only compiles the tools sub-directory
  • The tools subdirectory contains the vhd-util utility used to convert a RAW disk image into VHD format

2. Create a vanilla Ubuntu 14.04 UEC QCOW Image

  • Downloads a Ubuntu 14.04 UEC QCOW image, if an existing QCOW image is not provided
  • Mounts the QCOW image
  • Bootstraps the image with the necessary modifications needed for the Rackspace Public Cloud (via chroot)
  • Unmounts the QCOW image


$ ./

Outputs: trusty-server-cloudimg-amd64-disk1.img

  • A vanilla Ubuntu 14.04 QCOW image that has been modified for the Public Cloud

  • Note: If you want to make custom changes to the OS, this is your chance to do so

    • Mount the QCOW image as done in the, then via chroot, make any necessary changes you wish to persist

3. Convert the QCOW to VHD

  • First, the script converts the QCOW to RAW as vhd-util expects RAW
  • Then, it converts the RAW image into VHD using vhd-util


$ ./ ./trusty-server-cloudimg-amd64-disk1.img .

Outputs: trusty-server-cloudimg-amd64-disk1.vhd

  • A Ubuntu 14.04 VHD image that is ready for the Public Cloud

4. Upload the VHD image to Cloud Files & register the image in Cloud Images

  • Uses pyrax to upload the new VHD image up to the Rackspace Public Cloud region with the custom image name provided
    • Specifically, uploads the VHD to the Cloud Files in the specified region
    • Then, registers the image with Cloud Images


python ORD trusty-server-cloudimg-amd64-disk1.vhd "my_ubuntu_1404"

5. Boot a VM with the newly registered custom image

nova boot --image="my_ubuntu_1404" --flavor=performance1-2 my_ubuntu_1404_test

About the Author

Mike Metral is a Solution Architect at Rackspace in the Private Cloud Product organization. Mike joined Rackspace in 2012 with the intent of helping OpenStack become the open standard for cloud management. At Rackspace, Mike has led the integration effort with strategic partner RightScale; aided in the assessment, development, and evolution of Rackspace Private Cloud; as well as served as the Chief Architect of the Service Provider Program. Prior to joining Rackspace, Mike held senior technical roles at Sandia National Laboratories performing research and development in Cyber Security with regards to distributed systems, cloud and mobile computing. You can follow Mike on Twitter @mikemetral and Github as metral

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