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Ubuntu Packer Templates for MAAS

Introduction

The Packer templates in this directory creates Ubuntu images for use with MAAS.

Prerequisites (to create the image)

  • A machine running Ubuntu 18.04+ with the ability to run KVM virtual machines.
  • qemu-utils, libnbd-bin, nbdkit and fuse2fs
  • qemu-system
  • qemu-system-modules-spice (If building on Ubuntu 24.04 LTS "Noble")
  • ovmf
  • cloud-image-utils
  • parted
  • Packer, v1.7.0 or newer

Requirements (to deploy the image)

ubuntu-cloudimg.pkr.hcl

This template builds a tgz image from the official Ubuntu cloud images. This results in an image that is very close to the ones that are on https://images.maas.io/.

Building the image

The build the image you give the template a script which has all the customizations:

packer init .
packer build -var customize_script=my-changes.sh -var ubuntu_series=jammy \
    -only='cloudimg.*' .

my-changes.sh is a script you write which customizes the image from within the VM. For example, you can install packages using apt-get, call out to ansible, or whatever you want.

Building using make:

make custom-cloudimg.tar.gz SERIES=jammy

Accessing external files from you script

If you want to put or use some files in the image, you can put those in the http directory.

Whatever file you put there, you can access from within your script like this:

wget http://${PACKER_HTTP_IP}:${PACKER_HTTP_PORT}:/my-file

Installing a kernel

Usually, images used by MAAS don't include a kernel. When a machine is deployed in MAAS, the appropriate kernel is chosen for that machine and installed on top of the chosen image.

If you do want to force an image to always use a specific kernel, you can include it in the image.

The easiest way of doing this is to use the kernel parameter:

packer init .
packer build -var kernel=linux-lowlatency -var customize_script=my-changes.sh \
    -only='cloudimg.*' .

You can also install the kernel manually in your my-changes.sh script, but in that case you also need to write the name of the kernel package to /curtin/CUSTOM_KERNEL. This is to ensure that MAAS won't install another kernel on deploy.

Building different architectures

By default, images are produces for amd64. You can build for arm64 as well if you specify the architecture parameter:

packer init .
packer build -var architecture=arm64 -var customize_script=my-changes.sh \
    -only='cloudimg.*' .

ubuntu-flat.pkr.hcl and ubuntu-lvm.pkr.hcl

These templates use an Ubuntu server image to install the image to the VM. It takes longer than using a cloud image, but can be useful for certain use cases.

Customizing the Image

It is possible to customize the image either during the Ubuntu installation or afterwards, before packing the final image. The former is done by providing autoinstall config, editing the user-data-flat and user-data-lvm files. The latter is performed by the install-custom-packages script.

Building the image using a proxy

The Packer template downloads the Ubuntu net installer from the Internet. To tell Packer to use a proxy set the HTTP_PROXY environment variable to your proxy server. Alternatively you may redefine iso_url to a local file, set iso_checksum_type to none to disable checksuming, and remove iso_checksum_url.

Building an image

You can easily build the image using the Makefile:

make custom-ubuntu-lvm.dd.gz

to build a raw image with LVM, alternatively, you can build a TGZ image

make custom-ubuntu.tar.gz

You can also manually run packer. Your current working directory must be in packer-maas/ubuntu, where this file is located. Once in packer-maas/ubuntu you can generate an image with:

packer init .
PACKER_LOG=1 packer build -only=qemu.lvm .

or

packer init .
PACKER_LOG=1 packer build -only=qemu.flat .

Note: ubuntu-lvm.pkr.hcl and ubuntu-flat.pkr.hcl are configured to run Packer in headless mode. Only Packer output will be seen. If you wish to see the installation output connect to the VNC port given in the Packer output or change the value of headless to false in the HCL2 file.

Installation is non-interactive. Note that the installation will attempt an SSH connection to the QEMU VM where the newly-built image is being booted. This is the final provisioning step in the process. Packer uses SSH to discover that the image has, in fact, booted, so there may be a number of failed tries -- over 3-5 minutes -- until the connection is successful. This is normal behavior for packer.

Makefile Parameters

PACKER_LOG

Enable (1) or Disable (0) verbose packer logs. The default value is set to 0.

SERIES

Specify the Ubuntu Series to build. The default value is set to Jammy.

ARCH

Target image architecture. Supported values are amd64 (default) and arm64.

URL

The URL prefix for mirror that is hosting the ISO images for a given series. The default value is set to http://releases.ubuntu.com. ISO images are expected to be under URL/SERIES/.

SUMS

The file name for the checksums file. The default value is set to SHA256SUMS.

TIMEOUT

The timeout to apply when building the image. The default value is set to 1h.

Default Username

The default username is ubuntu

Uploading images to MAAS

TGZ image

maas admin boot-resources create \
    name='custom/ubuntu-tgz' \
    title='Ubuntu Custom TGZ' \
    architecture='amd64/generic' \
    filetype='tgz' \
    content@=custom-cloudimg.tar.gz

LVM raw image

maas admin boot-resources create \
    name='custom/ubuntu-raw' \
    title='Ubuntu Custom RAW' \
    architecture='amd64/generic' \
    filetype='ddgz' \
    content@=custom-ubuntu-lvm.dd.gz