Chapter 3. Working with overcloud images

Red Hat OpenStack Platform (RHOSP) director provides images for the overcloud. The QCOW image in this collection contains a base set of software components that integrate to form various overcloud roles, such as Compute, Controller, and storage nodes. In some situations, you might aim to modify certain aspects of the overcloud image to suit your needs, such as installing additional components to nodes.

You can use the virt-customize tool to modify an existing overcloud image to augment an existing Controller node. For example, use the following procedures to install additional ml2 plugins, Cinder backends, or monitoring agents that do not ship with the initial image.


If you modify the overcloud image to include third-party software and report an issue, Red Hat might request that you reproduce the issue with an unmodified image in accordance with our general third-party support policy:

3.1. Obtaining the overcloud images

Director requires several disk images to provision overcloud nodes:

  • An introspection kernel and ramdisk - For bare metal system introspection over PXE boot.
  • A deployment kernel and ramdisk - For system provisioning and deployment.
  • An overcloud kernel, ramdisk, and full image - A base overcloud system that director writes to the hard disk of the node.


  1. To obtain these images, install the rhosp-director-images and rhosp-director-images-ipa packages:

    $ sudo dnf install rhosp-director-images rhosp-director-images-ipa
  2. Extract the archives to the images directory on the stack user home, /home/stack/images:

    $ cd ~/images
    $ for i in /usr/share/rhosp-director-images/overcloud-full-latest-16.2.tar /usr/share/rhosp-director-images/ironic-python-agent-latest-16.2.tar; do tar -xvf $i; done

3.2. Initrd: Modifying the initial ramdisks

Some situations might require that you modify the initial ramdisk. For example, you might require that a certain driver is available when you boot the nodes during the introspection or provisioning processes. In the context of the overcloud, this includes one of the following ramdisks:

  • The introspection ramdisk - ironic-python-agent.initramfs
  • The provisioning ramdisk - overcloud-full.initrd

This procedure adds an additional RPM package to the ironic-python-agent.initramfs ramdisk as an example.


  • You have installed the pax utility:

    $ sudo dnf install -y spax


  1. Log in as the root user and create a temporary directory for the ramdisk:

    # mkdir ~/ipa-tmp
    # cd ~/ipa-tmp
  2. Use the skipcpio and cpio commands to extract the ramdisk to the temporary directory:

    # /usr/lib/dracut/skipcpio ~/images/ironic-python-agent.initramfs | zcat | cpio -ivd | pax -r
  3. Install an RPM package to the extracted contents:

    # rpm2cpio ~/RPMs/python-proliantutils-2.1.7-1.el7ost.noarch.rpm | pax -r
  4. Recreate the new ramdisk:

    # find . 2>/dev/null | cpio --quiet -c -o | gzip -8  > /home/stack/images/ironic-python-agent.initramfs
    # chown stack: /home/stack/images/ironic-python-agent.initramfs
  5. Verify that the new package now exists in the ramdisk:

    # lsinitrd /home/stack/images/ironic-python-agent.initramfs | grep proliant

3.3. QCOW: Installing virt-customize to director

The libguestfs-tools package contains the virt-customize tool.


  • Install the libguestfs-tools from the rhel-8-for-x86_64-appstream-eus-rpms repository:

    $ sudo dnf install libguestfs-tools

If you install the libguestfs-tools package on the undercloud, disable iscsid.socket to avoid port conflicts with the tripleo_iscsid service on the undercloud:

$ sudo systemctl disable --now iscsid.socket

3.4. QCOW: Inspecting the overcloud image

Before you can review the contents of the overcloud-full.qcow2 image, you must create a virtual machine that uses this image.


  1. To create a virtual machine instance that uses the overcloud-full.qcow2 image, use the guestmount command:

    $ mkdir ~/overcloud-full
    $ guestmount -a overcloud-full.qcow2 -i --ro ~/overcloud-full

    You can review the contents of the QCOW2 image in ~/overcloud-full.

  2. Alternatively, you can use virt-manager to create a virtual machine with the following boot options:

    • Kernel path: /overcloud-full.vmlinuz
    • initrd path: /overcloud-full.initrd
    • Kernel arguments: root=/dev/sda

3.5. QCOW: Setting the root password

Set the root password to provide administrator-level access for your nodes through the console.


  • Set the password for the root user on image:

    $ virt-customize --selinux-relabel -a overcloud-full.qcow2 --root-password password:test
    [  0.0] Examining the guest ...
    [ 18.0] Setting a random seed
    [ 18.0] Setting passwords
    [ 19.0] Finishing off

3.6. QCOW: Registering the image

Register your overcloud image to the Red Hat Content Delivery Network.


  1. Register your image temporarily to enable Red Hat repositories relevant to your customizations:

    $ virt-customize --selinux-relabel -a overcloud-full.qcow2 --run-command 'subscription-manager register --username=[username] --password=[password]'
    [  0.0] Examining the guest ...
    [ 10.0] Setting a random seed
    [ 10.0] Running: subscription-manager register --username=[username] --password=[password]
    [ 24.0] Finishing off
  2. Replace the [username] and [password] with your Red Hat customer account details. This runs the following command on the image:

    subscription-manager register --username=[username] --password=[password]

3.7. QCOW: Attaching a subscription and enabling Red Hat repositories


  1. Find a list of pool ID from your account subscriptions:

    $ sudo subscription-manager list
  2. Choose a subscription pool ID and attach it to the image:

    $ virt-customize --selinux-relabel -a overcloud-full.qcow2 --run-command 'subscription-manager attach --pool [subscription-pool]'
    [  0.0] Examining the guest ...
    [ 12.0] Setting a random seed
    [ 12.0] Running: subscription-manager attach --pool [subscription-pool]
    [ 52.0] Finishing off
  3. Replace the [subscription-pool] with your chosen subscription pool ID:

    subscription-manager attach --pool [subscription-pool]

    This adds the pool to the image so that you can enable the repositories.

  4. Enable the Red Hat repositories:

    $ subscription-manager repos --enable=[repo-id]

3.8. QCOW: Copying a custom repository file

Adding third-party software to the image requires additional repositories. The following is an example repo file that contains configuration to use the OpenDaylight repository content.


  1. List the contents of the opendaylight.repo file:

    $ cat opendaylight.repo
    name=OpenDaylight Repository
  2. Copy the repository file on to the image:

    $ virt-customize --selinux-relabel -a overcloud-full.qcow2 --upload opendaylight.repo:/etc/yum.repos.d/
    [  0.0] Examining the guest ...
    [ 12.0] Setting a random seed
    [ 12.0] Copying: opendaylight.repo to /etc/yum.repos.d/
    [ 13.0] Finishing off

    The --upload option copies the repository file to /etc/yum.repos.d/ on the overcloud image.


Red Hat does not offer support for software from non-certified vendors. Check with your Red Hat support representative that the software you want to install is supported.

3.9. QCOW: Installing RPMs


  • Use the virt-customize command to install packages to the image:

    $ virt-customize --selinux-relabel -a overcloud-full.qcow2 --install opendaylight
    [  0.0] Examining the guest ...
    [ 11.0] Setting a random seed
    [ 11.0] Installing packages: opendaylight
    [ 91.0] Finishing off

    Use the --install option to specify a package to install.

3.10. QCOW: Cleaning the subscription pool


  • After you install the necessary packages to customize the image, remove the subscription pools and unregister the image:

    $ virt-customize --selinux-relabel -a overcloud-full.qcow2 --run-command 'subscription-manager remove --all'
    [  0.0] Examining the guest ...
    [ 12.0] Setting a random seed
    [ 12.0] Running: subscription-manager remove --all
    [ 18.0] Finishing off

3.11. QCOW: Unregistering the image


  • Unregister the image so that the overcloud deployment process can deploy the image to your nodes and register each of them individually:

    $ virt-customize --selinux-relabel -a overcloud-full.qcow2 --run-command 'subscription-manager unregister'
    [  0.0] Examining the guest ...
    [ 11.0] Setting a random seed
    [ 11.0] Running: subscription-manager unregister
    [ 17.0] Finishing off

3.12. QCOW: Reset the machine ID


  • Reset the machine ID for the image so that machines that use this image do not use duplicate machine IDs:

    $ virt-sysprep --operation machine-id -a overcloud-full.qcow2

3.13. Uploading the images to director

After you modify the image, you need to upload it to director.


  1. Source the stackrc file so that you can access director from the command line:

    $ source stackrc
  2. Upload the default director images to use for deploying the overcloud:

    $ openstack overcloud image upload --image-path /home/stack/images/

    This uploads the following images into the director:

    • bm-deploy-kernel
    • bm-deploy-ramdisk
    • overcloud-full
    • overcloud-full-initrd
    • overcloud-full-vmlinuz

      The script also installs the introspection images on the directors PXE server.

  3. View a list of the images in the CLI:

    $ openstack image list
    | ID                                   | Name                   |
    | 765a46af-4417-4592-91e5-a300ead3faf6 | bm-deploy-ramdisk      |
    | 09b40e3d-0382-4925-a356-3a4b4f36b514 | bm-deploy-kernel       |
    | ef793cd0-e65c-456a-a675-63cd57610bd5 | overcloud-full         |
    | 9a51a6cb-4670-40de-b64b-b70f4dd44152 | overcloud-full-initrd  |
    | 4f7e33f4-d617-47c1-b36f-cbe90f132e5d | overcloud-full-vmlinuz |

    This list does not show the introspection PXE images (agent.*). Director copies these files to /httpboot.

    [stack@host1 ~]$ ls /httpboot -l
    total 151636
    -rw-r--r--. 1 ironic ironic       269 Sep 19 02:43 boot.ipxe
    -rw-r--r--. 1 root   root         252 Sep 10 15:35 inspector.ipxe
    -rwxr-xr-x. 1 root   root     5027584 Sep 10 16:32 agent.kernel
    -rw-r--r--. 1 root   root   150230861 Sep 10 16:32 agent.ramdisk
    drwxr-xr-x. 2 ironic ironic      4096 Sep 19 02:45 pxelinux.cfg