Overcloud host disk image build

This section covers configuration for building overcloud host disk images with Diskimage builder (DIB), which is available from the Yoga 12.0.0 release. This configuration is applied in ${KAYOBE_CONFIG_PATH}/overcloud-dib.yml.

Enabling host disk image build

From the Yoga release, disk images for overcloud hosts can be built directly using Diskimage builder rather than through Bifrost. This is enabled with the following option:


Whether to build host disk images with DIB directly instead of through Bifrost. Setting it to true disables Bifrost image build and allows images to be built with the kayobe overcloud host image build command. Default value is false, except on Rocky where it is true. This will change in a future release.

With this option enabled, Bifrost will be configured to stop building a root disk image. This will become the default behaviour in a future release.

Overcloud root disk image configuration

Kayobe uses Diskimage builder (DIB) to build root disk images that are deployed to overcloud hosts when they are provisioned. The following options configure how these images are built. Consult the Diskimage-builder documentation for further information on building disk images.

The default configuration builds a whole disk (partitioned) image using the selected OS distribution (CentOS Stream 8 by default) with serial console enabled, and SELinux disabled if CentOS Stream or Rocky Linux is used. Cloud-init is used to process the configuration drive built by Bifrost during provisioning.


List of overcloud host disk images to build. Each element is a dict defining an image in a format accepted by the stackhpc.os-images role. Default is to build an image named deployment_image configured with the overcloud_dib_* variables defined below: {"name": "deployment_image", "elements": "{{ overcloud_dib_elements }}", "env": "{{ overcloud_dib_env_vars }}", "packages": "{{ overcloud_dib_packages }}"}.


DIB base OS element. Default is {{ 'rocky-container' if os_distribution == 'rocky' else os_distribution }}.


DIB image OS release. Default is {{ os_release }}.


List of default DIB elements. Default is ["centos", "cloud-init-datasources", "disable-selinux", "enable-serial-console", "vm"] when overcloud_dib_os_element is centos, or ["rocky-container", "cloud-init-datasources", "disable-selinux", "enable-serial-console", "vm"] when overcloud_dib_os_element is rocky or ["ubuntu", "cloud-init-datasources", "enable-serial-console", "vm"] when overcloud_dib_os_element is ubuntu. The vm element is poorly named, and causes DIB to build a whole disk image rather than a single partition.


List of additional DIB elements. Default is none.


List of DIB elements. Default is a combination of overcloud_dib_elements_default and overcloud_dib_elements_extra.


DIB default environment variables. Default is {"DIB_BOOTLOADER_DEFAULT_CMDLINE": "nofb nomodeset gfxpayload=text net.ifnames=1", "DIB_CLOUD_INIT_DATASOURCES": "ConfigDrive", "DIB_CONTAINERFILE_RUNTIME": "docker", "DIB_CONTAINERFILE_NETWORK_DRIVER": "host", DIB_RELEASE": "{{ overcloud_dib_os_release }}"}.


DIB additional environment variables. Default is none.


DIB environment variables. Default is combination of overcloud_dib_env_vars_default and overcloud_dib_env_vars_extra.


List of DIB packages to install. Default is to install no extra packages.


List of default git repositories containing Diskimage Builder (DIB) elements. See stackhpc.os-images role for usage. Default is empty.


List of additional git repositories containing Diskimage Builder (DIB) elements. See stackhpc.os-images role for usage. Default is empty.


List of git repositories containing Diskimage Builder (DIB) elements. See stackhpc.os-images role for usage. Default is a combination of overcloud_dib_git_elements_default and overcloud_dib_git_elements_extra.


Upper constraints file for installing packages in the virtual environment used for building overcloud host disk images. Default is {{ pip_upper_constraints_file }}.

Disk images are built with the following command:

(kayobe) $ kayobe overcloud host image build

It is worth noting that images will not be rebuilt if they already exist. To force rebuilding images, it is necessary to use the --force-rebuild argument.

(kayobe) $ kayobe overcloud host image build --force-rebuild

Example: Adding an element

In the following, we extend the list of DIB elements to add the growpart element:

  - "growpart"

Example: Building an XFS root filesystem image

By default, DIB will format the image as ext4. In some cases it might be useful to use XFS, for example when using the overlay Docker storage driver which can reach the maximum number of hardlinks allowed by ext4.

In DIB, we achieve this by setting the FS_TYPE environment variable to xfs.

  FS_TYPE: "xfs"

Example: Configuring a development user account


A development user account should not be used in production.

When debugging a failed deployment, it can sometimes be necessary to allow access to the image via a preconfigured user account with a known password. This can be achieved via the devuser element.

This example shows how to add the devuser element, and configure a username and password for an account that has passwordless sudo:

  - "devuser"

  DIB_DEV_USER_PASSWORD: "correct horse battery staple"

Alternatively, the dynamic-login element can be used to authorize SSH keys by appending them to the kernel arguments.

Example: Configuring custom DIB elements

Sometimes it is useful to use custom DIB elements that are not shipped with DIB itself. This can be done by sharing them in a git repository.

  - "my-element"

  - repo: "https://git.example.com/custom-dib-elements"
    local: "{{ source_checkout_path }}/custom-dib-elements"
    version: "master"
    elements_path: "elements"

In this example the master branch of https://git.example.com/custom-dib-elements would have a top level elements directory, containing a my-element directory for the element.

Example: Installing a package

It can be necessary to install additional packages in the root disk image. Rather than needing to write a custom DIB element, we can use the overcloud_dib_packages variable. For example, to install the biosdevname package:

  - "biosdevname"

Example: Building multiple images

It can be necessary to build multiple images to support the various types of hardware present in a deployment or the different functions performed by overcloud hosts. This can be configured with the overcloud_dib_host_images variable, using a format accepted by the stackhpc.os-images role. Note that image names should not include the file extension. For example, to build a second image with a development user account and the biosdevname package:

  - name: "deployment_image"
    elements: "{{ overcloud_dib_elements }}"
    env: "{{ overcloud_dib_env_vars }}"
    packages: "{{ overcloud_dib_packages }}"
  - name: "debug_deployment_image"
    elements: "{{ overcloud_dib_elements + ['devuser'] }}"
    env: "{{ overcloud_dib_env_vars | combine(devuser_env_vars) }}"
    packages: "{{ overcloud_dib_packages + ['biosdevname'] }}"

  DIB_DEV_USER_PASSWORD: "correct horse battery staple"

Running the kayobe overcloud host image build command with this configuration will create two images: deployment_image.qcow2 and debug_deployment_image.qcow2.

Disk image deployment configuration

See disk image deployment configuration in Bifrost for how to configure the root disk image to be used to provision each host.