LXD and OpenStack images

LXD is an open-source tool for orchestrating virtual machines and system containers. It is image based, and provides support for a large number of distributions and architectures.

OpenStack is an open-source cloud platform designed to create and manage cloud resources. By aggregating physical resources such as distributed compute, network, and storage into a pool, OpenStack then allocates virtual resources on-demand to users out of this pool. It does not handle virtualisation itself, but acts as a wrapper that leverages existing virtualisation technologies.

What are these images?

Canonical provides cloud image artefacts on cloud-images.ubuntu.com that have been customised to run on public clouds, including LXD and OpenStack. To learn more about these artefacts and supported architectures, visit our Ubuntu cloud image artefacts documentation.

How do you access them?

Go to cloud-images.ubuntu.com and select a release. For the latest LTS release, Ubuntu 24.04 LTS Noble Numbat, you would navigate to noble > current. Note that all artefacts are architecture specific, in the format <release>-<type>-cloudimg-<architecture>-<artefact>.

LXD and OpenStack also have minimal cloud images: Ubuntu images that have a reduced runtime footprint, optimised kernel and boot process. They are smaller and boot faster, but are not designed for environments requiring human interaction or debugging.

LXD images

To import an image into LXD, you will need two artefacts:

  1. A LXD tarball:

    • The LXD tarball artefact has the extension *.lxd.tar.xz

    • It contains the metadata needed by LXD to instantiate a container or virtual machine as well as a folder for any custom templates

  2. A file system for a container or a bootable disk image for a virtual machine:

The following are example commands to import an image for creating LXD containers and virtual machines based on downloaded Ubuntu 24.04 artefacts:

lxc image import noble-server-cloudimg-amd64-lxd.tar.xz \
   noble-server-cloudimg-amd64-root.tar.xz --alias noble_container

lxc image import noble-server-cloudimg-amd64-lxd.tar.xz \
   noble-server-cloudimg-amd64.img --alias noble_vm

OpenStack images

OpenStack uses QCOW images. Download the artefact for your chosen architecture with the *.img extension.

Use the OpenStack command-line client to interact with OpenStack. An example of uploading an image looks something like this:

openstack image create “Ubuntu-24.04” \
   --file noble-server-cloudimg-amd64.img \
   --disk-format qcow2 \
   --container-format bare \
   --public

To learn more about managing images with OpenStack, you can refer to the Manage images section of their documentation.

How do you configure them?

Configuring an Ubuntu cloud image allows you to make changes that tailor the image to your specific use case. You can automate the creation of user accounts, configure SSH access, or install software before the instance starts.

LXD images

You can configure your cloud images in LXD either before you import them or after. Configuring your images before importing them is most commonly done by editing the metadata.yaml file contained in the LXD tarball. Configuring your images after importing them is done through the CLI.

If you are interested in configuration of LXD containers rather than images, take a look at the Ubuntu Server LXD containers documentation.

Configuring metadata

LXD metadata is stored in the metadata.yaml file in the LXD tarball. This file contains all of the information needed to run an image in LXD. To make changes to this file, you will have to:

  1. Uncompress the LXD tarball.

  2. Make modifications to the metadata.yaml file. See the LXD image format documentation to learn more about image metadata and the templates you may wish to modify.

  3. Compress the metadata and templates.

This snippet from the How to customise LXD image metadata for cloud-init guide referenced below demonstrates a typical workflow:

# Uncompress original LXD metadata
$ tar xf ${RELEASE}-server-cloudimg-amd64-lxd.tar.xz
# Add directives to create /etc/cloud/cloud.cfg.d/95-use-lxd.cfg
$ cat > templates/cloud-init-use-lxd.tpl <<EOF
# Added by LXD metadata.yaml
datasource_list: [ LXD, NoCloud ]
EOF
$ cat > add-lxd.yaml <<EOF
    /etc/cloud/cloud.cfg.d/95-use-lxd.cfg:
        when:
            - create
            - copy
        template: cloud-init-use-lxd.tpl
EOF
$ cat add-lxd.yaml >> metadata.yaml
# Compress LXD metadata and templates
$ tar -czf ${RELEASE}-server-cloudimg-amd64-prefer-lxd.tar.xz metadata.yaml templates/

Configuring cloud-init

Cloud-init is used to initialise cloud instances on first boot. Refer to How to customise LXD image metadata for cloud-init for a guide on configuring cloud-init for LXD before initialisation. If you want to configure cloud-init once an instance has been created (but not booted), refer to the LXD docs on cloud-init.

Configuring after import using CLI

The LXD documentation on images has an extensive guide on managing images. Two of the most common use cases are to set individual properties or to edit all of the image properties.

# set a specific image property
lxc image set-property <image_ID> <key> <value>

# edit the full image properties
lxc image edit <image_ID>

OpenStack images

OpenStack has an extensive guide on modifying images that is applicable to the QCOW images Ubuntu provides. It leverages libguestfs tools in order to access and modify disk images. You can use the guestfish interactive shell (which exposes the full functionality of the guestfs API) or rely on the virt-* tools from libguestfs to perform specific tasks. For instance, use virt-cat for displaying files, virt-df for checking free space and virt-inspector for inspecting VM images.