ubuntuPackerImage

this guide will show you how to install packer and build an customize ubuntu 24.04 image which could run in multipass.

tested version

• packer 1.12.0
• qemu 8.2.2
• ubuntu 24.04
• multipass 1.14.1
• docker 28.0.4

multipass

in ubuntu server

sudo snap install multipass

packer

install packer at ubuntu 24.04 with brew

sudo apt-get install build-essential
/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
# add homebrew to path
eval "$(/home/linuxbrew/.linuxbrew/bin/brew shellenv)"
brew tap hashicorp/tap
brew install hashicorp/tap/packer
sudo apt-get install -y qemu-system-x86

build image with packer, run with multipass

The packer generated image (local customize image) is also a cloud image. But only multipass running in ubuntu server will accept the local customize image.

packer init template.pkr.hcl
packer build template.pkr.hcl
multipass launch file://$PWD/output-autogenerated_1/packer-autogenerated_1
# you also can overwrite sources.list by --cloud-init
multipass launch file://$PWD/output-autogenerated_1/packer-autogenerated_1 --cloud-init cloud-config.yaml

Multipass requires ubuntu server that support virtualization cpu. I tested in bare-metal ubuntu server. I also tested with ubuntu server VM hosted in windows 10 hyper-v with ExposeVirtualizationExtensions. That means VM in VM still works.

Notes about current template.pkr.hcl

Current packer template shows that how to install docker with defualt ubuntu image.

From line 48 to 61.

  provisioner "file" {
    destination = "/tmp/sources.list"
    source      = "sources.list"
  }

  provisioner "shell" {
    execute_command = "sudo sh -c '{{ .Vars }} {{ .Path }}'"
    inline          = ["cp /tmp/sources.list /etc/apt/sources.list.d/ubuntu.sources"]
    remote_folder   = "/tmp"
  }

  provisioner "shell" {
    scripts = ["install_docker.sh"]
  }

It replaces defualt sources.list so that you could change mirror to your specific location. This could help to speedup apt-get update command during docker installing process. But your mirror would be remove during next cloud-init.

From line 63 to 83

  provisioner "shell" {
    execute_command = "sudo sh -c '{{ .Vars }} {{ .Path }}'"
    inline          = [
      "/usr/bin/apt-get clean",
      "rm -r /etc/netplan/50-cloud-init.yaml /etc/ssh/ssh_host* /etc/sudoers.d/90-cloud-init-users",
      "/usr/bin/truncate --size 0 /etc/machine-id",
      "/usr/bin/gawk -i inplace '/PasswordAuthentication/ { gsub(/yes/, \"no\") }; { print }' /etc/ssh/sshd_config",
      "rm -r /root/.ssh",
      "rm /snap/README",
      "find /usr/share/netplan -name __pycache__ -exec rm -r {} +",
      "rm /var/cache/pollinate/seeded /var/cache/motd-news",
      "rm -r /var/cache/snapd/*",
      "rm -r /var/lib/cloud /var/lib/dbus/machine-id /var/lib/private /var/lib/systemd/timers /var/lib/systemd/timesync /var/lib/systemd/random-seed",
      "rm /var/lib/ubuntu-release-upgrader/release-upgrade-available",
      "rm /var/lib/update-notifier/fsck-at-reboot",
      "find /var/log -type f -exec rm {} +",
      "rm -r /tmp/* /tmp/.*-unix /var/tmp/*",
      "/bin/sync",
      "/sbin/fstrim -v /"]
    remote_folder   = "/tmp"
  }

It cleans the image after installation process. I mainly copy it from https://multipass.run/docs/building-multipass-images-with-packer but made some changes for ubuntu 24.04 and converted to hcl format. I also remove the step of reseting user/group process because it will delete docker group and the final image will fail.

Other topic

The original goal of my study is to automatically deploy a docker cluster with multipass. But bad luck, many limitation if you don't run multipass in ubuntu server.

Docker cluster

If your multipass running in ubuntu server, you also could config static ip.

This is the script to install multipass and config static ip interface setupMultipassWithFixIP.sh. The details will be explained in other guide.

If you successful build the image, config multipass with static ip, then you could initialize docker cluster with initDockerCluster.sh.

If your multipass running in windows or mac, you need to install docker when launching a new instance. You may take a look of initDockerClusterWithoutStaticIp.sh. I did not verify the script every update because of network bandwidth.

If your ubuntu server running in windows hyper-v, you can also expose virtualization to it and you can run mulitpass in it. Shutdown the vm and type following command with administrator.

Set-VMProcessor -VMName YOUR_VM_NAME -ExposeVirtualizationExtensions $true

Packer in macOS

If you use macOS, packer is fine, but your multipass does not accept local image;

Instead, I use lima for testing packer output image

brew tap hashicorp/tap
brew install hashicorp/tap/packer
brew install qemu
packer build template.pkr.hcl

brew install lima
# if path variable not update, logout and login again

# update ABSOLUTE_PATH_TO_YOU_IMAGE in lima-packer-docker.yaml
limactl create --name packer-docker lima-packer-docker.yaml
limactl start packer-docker
limactl shell packer-docker

docker node update --availability drain node21 docker node update --availability active node21 docker node demote node21