Creation of Windows Images – Openstack

If you want to build a Windows image for use in your OpenStack environment, you can follow the example in the official documentation, or you can grab a Windows 2012r2 evaluation pre-built image from the nice folks atCloudBase.

The CloudBase-provided image is built using a set of scripts and configuration files that CloudBase has made available on GitHub.

The CloudBase repository is an excellent source of information, but I wanted to understand the process myself. This post describes the process I went through to establish an automated process for generating a Windows image suitable for use with OpenStack.

Unattended windows installs

The Windows installer supports fully automated installations through the use of an answer file, or “unattend” file, that provides information to the installer that would otherwise be provided manually. The installer will look in a number of places to find this file. For our purposes, the important fact is that the installer will look for a file namedautounattend.xml in the root of all available read/write or read-only media. We’ll take advantage of this by creating a file config/autounattend.xml, and then generating an ISO image like this:

mkisofs -J -r -o config.iso config

And we’ll attach this ISO to a vm later on in order to provide the answer file to the installer.

So, what goes into this answer file?

The answer file is an XML document enclosed in an <unattend>..</unattend> element. In order to provide all the expected XML namespaces that may be used in the document, you would typically start with something like this:

<?xml version="1.0" ?>

  <!-- your content goes here -->


Inside this <unattend> element you will put one or more <settings> elements, corresponding to the differentconfiguration passes of the installer:

<settings pass="specialize">

The available configuration passes are:

Of these, the most interesting for our use will be:

  • windowsPE — used to install device drivers for use within the installer environment. We will use this to install the VirtIO drivers necessary to make VirtIO devices visible to the Windows installer.
  • specialize — In this pass, the installer applies machine-specific configuration. This is typically used to configure networking, locale settings, and most other things.
  • oobeSystem — In this pass, the installer configures things that happen at first boot. We use this to step to install some additional software and run sysprep in order to prepare the image for use in OpenStack.

Inside each <settings> element we will place one or more <component> elements that will apply specific pieces of configuration. For example, the following <component> configures language and keyboard settings in the installer:

<settings pass="windowsPE">
  <component name="Microsoft-Windows-International-Core-WinPE"


Technet provides documentation on the available components.

Cloud-init for Windows

Cloud-init is a tool that will configure a virtual instance when it first boots, using metadata provided by the cloud service provider. For example, when booting a Linux instance under OpenStack, cloud-init will contact the OpenStack metadata service at in order to retrieve things like the system hostname, SSH keys, and so forth.

While cloud-init has support for Linux and BSD, it does not support Windows. The folks at Cloudbase have produced cloudbase-init in order to fill this gap. Once installed, the cloudbase-init tool will, upon first booting a system:

  • Configure the network using information provided in the cloud metadata
  • Set the system hostname
  • Create an initial user account (by default “Admin”) with a randomly generated password (see below for details)
  • Install your public key, if provided
  • Execute a script provided via cloud user-data

Passwords and ssh keys

While cloudbase-init will install your SSH public key (by default into /Users/admin/.ssh/authorized_keys), Windows does not ship with an SSH server and cloudbase-init does not install one. So what is it doing with the public key?

While you could arrange to install an ssh server that would make use of the key, cloudbase-init uses it for a completely unrelated purpose: encrypting the randomly generated password. This encrypted password is then passed back to OpenStack, where you can retrieve it using the nova get-password command, and decrypt it using the corresponding SSH private key.

Running nova get-password myinstance will return something like:


Providing your secret key as an additional parameter will decrypt the password:

$ nova get-password myinstance ~/.ssh/id_rsa

With an appropriately configured image, you could connect using an RDP client and log in as the “Admin” user using that password.

Passwords without ssh keys

If you do not provide your instance with an SSH key you will not be able to retrieve the randomly generated password. However, if you can get console access to your instance (e.g., via the Horizon dashboard), you can log in as the “Administrator” user, at which point you will be prompted to set an initial password for that account.


You can find logs for cloudbase-init in c:\program files (x86)\cloudbase solutions\cloudbase-init\log\cloudbase-init.log.

If appropriately configured, cloudbase-init will also log to the virtual serial port. This log is available in OpenStack by running nova console-log <instance>. For example:

$ nova console-log my-windows-server
2014-11-19 04:10:45.887 1272 INFO cloudbaseinit.init [-] Metadata service loaded: 'HttpService'
2014-11-19 04:10:46.339 1272 INFO cloudbaseinit.init [-] Executing plugin 'MTUPlugin'
2014-11-19 04:10:46.371 1272 INFO cloudbaseinit.init [-] Executing plugin 'NTPClientPlugin'
2014-11-19 04:10:46.387 1272 INFO cloudbaseinit.init [-] Executing plugin 'SetHostNamePlugin'

Putting it all together

I have an install script that drives the process, but it’s ultimately just a wrapper for virt-install and results in the following invocation:

exec virt-install -n ws2012 -r 2048 \
  -w network=default,model=virtio \
  --disk path=$TARGET_IMAGE,bus=virtio \
  --cdrom $WINDOWS_IMAGE \
  --disk path=$VIRTIO_IMAGE,device=cdrom \
  --disk path=$CONFIG_IMAGE,device=cdrom \
  --os-type windows \
  --os-variant win2k8 \
  --vnc \
  --console pty

Where TARGET_IMAGE is the name of a pre-existing qcow2 image onto which we will install Windows, WINDOWS_IMAGE is the path to an ISO containing Windows Server 2012r2, VIRTIO_IMAGE is the path to an ISO containing VirtIO drivers for Windows (available from the Fedora project), and CONFIG_IMAGE is a path to the ISO containing our autounattend.xmlfile.

The fully commented autounattend.xml file, along with the script mentioned above, are available in my windows-openstack-image repository on GitHub.

The answer file in detail


In the windowsPE phase, we start by configuring the installer locale settings:

<component name="Microsoft-Windows-International-Core-WinPE"



And installing the VirtIO drviers using the Microsoft-Windows-PnpCustomizationsWinPE component:

<component name="Microsoft-Windows-PnpCustomizationsWinPE"
  publicKeyToken="31bf3856ad364e35" language="neutral"
  versionScope="nonSxS" processorArchitecture="amd64">

    <PathAndCredentials wcm:action="add" wcm:keyValue="1">


This assumes that the VirtIO image is mounted as drive d:.

With the drivers installed, we can then call the Microsoft-Windows-Setup component to configure the disks and install Windows. We start by configuring the product key:

<component name="Microsoft-Windows-Setup"


And then configure the disk with a single partition (that will grow to fill all the available space) which we then format with NTFS:

    <Disk wcm:action="add">

        <CreatePartition wcm:action="add">

        <ModifyPartition wcm:action="add">

We provide information about what to install:


          <Value>Windows Server 2012 R2 SERVERSTANDARDCORE</Value>

And where we would like it installed:



In the specialize phase, we start by setting the system name to a randomly generated value using the Microsoft-Windows-Shell-Setup component:

<component name="Microsoft-Windows-Shell-Setup"
  publicKeyToken="31bf3856ad364e35" language="neutral"
  versionScope="nonSxS" processorArchitecture="amd64">

We enable remote desktop because in an OpenStack environment this will probably be the preferred mechanism with which to connect to the host (but see this document for an alternative mechanism).

First, we need to permit terminal server connections:

<component name="Microsoft-Windows-TerminalServices-LocalSessionManager"

And we do not want to require network-level authentication prior to connecting:

<component name="Microsoft-Windows-TerminalServices-RDP-WinStationExtensions"

We will also need to open the necessary firewall group:

<component name="Networking-MPSSVC-Svc"
    <FirewallGroup wcm:action="add" wcm:keyValue="RemoteDesktop">

Finally, we use the Microsoft-Windows-Deployment component to configure the Windows firewall to permit ICMP traffic:

<component name="Microsoft-Windows-Deployment"
  language="neutral" versionScope="nonSxS">


    <RunSynchronousCommand wcm:action="add">
      <Path>netsh advfirewall firewall add rule name=ICMP protocol=icmpv4 dir=in action=allow</Path>

And to download the cloudbase-init installer and make it available for later steps:

    <RunSynchronousCommand wcm:action="add">
      <Path>powershell -NoLogo -Command "(new-object System.Net.WebClient).DownloadFile('', 'c:\Windows\Temp\cloudbase.msi')"</Path>

We’re using Powershell here because it has convenient methods available for downloading URLs to local files. This is roughly equivalent to using curl on a Linux system.


In the oobeSystem phase, we configure an automatic login for the Administrator user:


This automatic login only happens once, because we configure FirstLogonCommands that will first install cloudbase-init:

    <SynchronousCommand wcm:action="add">
      <CommandLine>msiexec /i c:\windows\temp\cloudbase.msi /qb /l*v c:\windows\temp\cloudbase.log LOGGINGSERIALPORTNAME=COM1</CommandLine>

And will then run sysprep to generalize the system (which will, among other things, lose the administrator password):

    <SynchronousCommand wcm:action="add">
      <CommandLine>c:\windows\system32\sysprep\sysprep /generalize /oobe /shutdown</CommandLine>

The system will shut down when sysprep is complete, leaving you with a Windows image suitable for uploading into OpenStack:

glance image-create --name ws2012 \
  --disk-format qcow2 \
  --container-format bare  \
  --file ws2012.qcow2


If you run into problems with an unattended Windows installation:

During the first stage of the installer, you can look in the x:\windows\panther directory for setupact.log andsetuperr.log, which will have information about the early install process. The x: drive is temporary, and files here will be discarded when the system reboots.

Subsequent installer stages will log to c:\windows\panther\.

If you are unfamiliar with Windows, the type command can be used very much like the cat command on Linux, and the more command provides paging as you would expect. The notepad command will open a GUI text editor/viewer.

You can emulate the tail command using powershell; to see the last 10 lines of a file:

C:\> powershell -command "Get-Content setupact.log -Tail 10"

Technet has a Deployment Troubleshooting and Log Files document that discusses in more detail what is logged and where to find it.


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