A declarative builder for QCOWs and ISOs
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Image Builder is a utility used to produce two types of artifacts needed for an airshipctl deployment: an iso (for the ephemeral node), and qcow2’s (used by metal3io to deploy all other nodes). This is accomplished through several stages as follows:

  1. Build docker image containing the base operating system and basic configuration management
  2. Run configuration management again with customized user-supplied inputs in container runtime
    • A more accessible layer for user customization that doesn't require rebuilding the container
    • Users may make their own decisions as to whether making a customized docker image build is worthwhile
  3. Container runtime produces a final image artifact (ISO or QCOW2)

The final QCOW2 image can be used:

  1. In the capm3-ironic deployment to deliver there that images to be used in BMH objects
  2. In manifests as KRM-function to get information about all Vars that were used to build that image, including the link to image-builder. See qcow-bundle metainformation section.

Airship Image Variations

The ISO is built using the network information defined by the ephemeral node in the supplied airship manifests. Therefore, each airship deployment should have its own ISO created.

The QCOW2’s have such networking information driven by cloud-init during metal3io deployment, and therefore is not contained in the image itself. These QCOWs would therefore not necessarily be generated for each unique airship deployment, but rather for each for unique host profile.

Note that we will refer to the QCOW2s as the “base OS” or “target OS”, rather than “baremetal OS”, since the same process can be used to build QCOW2s for baremetal and for a virtualized environment.

Building the image-builder container locally

If you do not wish to use the image-builder container published on quay.io, you may build your own locally as follows:

sudo apt -y install sudo git make
git clone https://review.opendev.org/airship/images
cd images/image-builder
sudo make DOCKER_REGISTRY=mylocalreg build

By default, both the ISO and QCOW share the same base container image. Therefore in most cases it should be sufficient to generate a single container that's reused for all image types and further differentiated in the container runtime phase described in the next section.

Executing the image-builder container

The following makefile target may be used to execute the image-builder container in order to produce an ISO or QCOW2 output.

sudo apt -y install sudo git make
git clone https://review.opendev.org/airship/images
cd images/image-builder
sudo make IMAGE_TYPE=qcow cut_image

In the above example, set IMAGE_TYPE to iso or qcow as appropriate. This will be passed into the container to instruct it which type of image to build. Also include DOCKER_REGISTRY override if you wish to use a local docker image as described in the previous section.

This makefile target uses config files provided in the images/image-builder/config directory. Modify these files as needed in order to customize your iso and qcow generation. This provides a good place for adding and testing customizations to build parameters, without needing to modify the ansible playbooks themselves.

Building behind a proxy

Example building docker container locally, plus ISO and qcow behind a proxy:

sudo apt -y install sudo git make
git clone https://review.opendev.org/airship/images
cd images/image-builder
# Create container
sudo make DOCKER_REGISTRY=mylocalreg PROXY=http://proxy.example.com:8080 build
# Create ephemeral ISO
sudo make DOCKER_REGISTRY=mylocalreg PROXY=http://proxy.example.com:8080 IMAGE_TYPE=iso cut_image
# Create qcow
sudo make DOCKER_REGISTRY=mylocalreg PROXY=http://proxy.example.com:8080 IMAGE_TYPE=qcow cut_image

Useful testing flags

The SKIP_MULTI_ROLE build flag is useful if you would like to test local updates to the osconfig playbook, or updates to custom configs for this playbook. This saves time since you do not need to rebuild the target filesystem. For example:

sudo make SKIP_MULTI_ROLE=true build

Similarly, osconfig and livecdcontent roles can be skipped using SKIP_OSCONFIG_ROLE and SKIP_LIVECDCONTENT_ROLE respectively. SKIP_LIVECDCONTENT_ROLE may be useful in combination with SKIP_MULTI_ROLE if you want to test out playbook changes to osconfig (however, it won't show up in the final bootable ISO image unless you don't skip SKIP_LIVECDCONTENT_ROLE).

Division of Configuration Management responsibilities

Configuration management of the base OS is divided into several realms, each with their own focus:

  1. Image-builder configuration data, i.e. data baked into the QCOW2 base image. The following should be used to drive this phase:

    1. The storage and compute elements of host/hardware profiles (kernel boot params, cpu pinning, hugepage settings, disk partitioning, etc), and
    2. Common operating system configurations applicable to all (or most) deployment scenarios.
    3. Custom-built kernel modules (e.g. dkms based installations, i40e driver, etc)
    4. Necessary components for the node’s bootstrap to k8s cluster, e.g. k8s, CNI, containerd, etc
    5. Any other operating system setting which would require a reboot or cannot otherwise be accommodated in #2 below
  2. Cloud-init driven configuration for site-specific data. Examples include:

    1. Hostnames, domain names, FQDNs, IP addresses, etc
    2. Network configuration data (bonding, MTU settings, VLANs, DNS, NTP, ethtool settings, etc)
    3. Certificates, SSH keys, user accounts and/or passwords, etc.
  3. HCA (host-config agent) for limited day-2 base-OS management

    1. Cron jobs
    2. Possible overlapping of configuration-management items with #1 - #2, but for zero-disruption day-2 management (kept to a minimum to reduce design & testing complexity, only essential things to minimize overhead.)
    3. Eventually HCA may be phased out if #1 and #2 become streamlined enough and impact minimized to the degree that SLAs can be met, and use of HCA may be reduced or eliminated over time.

QCOW bundle metainformation

QCOW bundle contains metainformation about Ansible var values that were used when the image was built. This information can be taken and used, because QCOW bundle is implemented as a KRM-function. See the example. NOTE: replace image: URL with the one you want to get information about. Execute kustomize build --enable-alpha-plugins <folder> and it will output something like:

apiVersion: airshipit.org/v1alpha1
kind: VariableCatalogue
  name: profile_multistrap
inventory_hostname_short: localhost
k8s_version: 1.18.6-00
  crashkernel: 768M

This VariableCatalogue contains all vars that were set when image-builder Docker images was built. To get that configPath: /profiles/profile_multistrap.json is used. This file is created during image-builder build process. Image-builder allows to override some parameters on QCOW-bundle generation. These values are also available and can be seen with configPath: /profiles/profile_qcow_<qcow-image-settings-folder-name>.json, e.g. configPath: /profiles/profile_control-plane.json or configPath: /profiles/profile_data-plane.json. That profile also contains information about the URL to image-builder that was used to product qcow-bundle: see field image_builder_image.

This information can be used to build manifests that don't have duplication. E.g. k8s version rather than to be set ALONG with url of qcow-bundle, can be taken from qcow-bundle. That means that it's possible only to put info about qcow-bundle and information about k8s that it contains will be available. This may also reduce the size of Catalogues in general.

The implementation is based on the following 2 playbook calls:

ansible-playbook -i assets/playbooks/inventory.yaml assets/playbooks/profile_generation.yaml
ansible-playbook -i assets/playbooks/inventory.yaml assets/playbooks/profile_resolution.yaml

As a result the file assets/playbooks/config.json will appear with all configurable image-builder variables resolved.

Supported OSes

  • Ubuntu 20.04 LTS


Q: Why is the build target slow? A: There is a mksquashfs command which runs as part of the build target, and performs slowly if your build environment lacks certain CPU flags which accelerate compression. Use "host-passthrough" or equivalent in your build environment to pass through these CPU flags. In libvirt domain XML, you would change your cpu mode element as follows: <cpu mode='host-passthrough' check='none'/>

How Zuul image artifacts are used by Airshipctl

+------------------------------------------------------+ +----------------------------------------+ | Built by Zuul | | Airshipctl Deployment Process | | | | | | | | | | +----------------------+ | | +--------------+ +---------------+ | | |Base container image +--+--+->| Ephemeral ISO|<---+ Site Manifests| | | |built by image-builder| | | +--------------+ +---------------+ | | +-----------+----------+ | | | | | | | | | +-----------------------+ +----------v-----------+ | | +---------------------------------+ | | |Profiles from +-->|QCOW container image +-+--+->| QCOWs hosted from this container| | | |image-builder/manifests| |built by image-builder| | | | image by airshipctl | | | +-----------------------+ +----------------------+ | | +------------------+--------------+ | | | | | | | +-------------------------+ | | +------------------v----------------+ | | |IPA container image +-+--+->|IPA image for node discovery. IPA | | | |built in airshipit/images| | | |deploys QCOW target image(s) pulled| | | +-------------------------+ | | |from hosted QCOW container above. | | | | | +-----------------------------------+ | +------------------------------------------------------+ +----------------------------------------+