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Packer Files

The most important files for the configuration of this packer frame work are found in the packer and templates directories. And they are discussed in detail here.

Packer Files

To customize the setup e.g. for adding a new release of an existing distribution there are a couple of files that are of importance under the packer directory. The scope of this section is limited to the non-shared files with the exception of common.auto.pkrvars.hcl.

common.auto.pkrvars.hcl

The settings in common.auto.pkrvars.hcl are valid for every image build but can be overridden individually in the OS specific pkrvars.hcl files described further down in the text.

# -----------------------------------------------------------------------------
# Comman variables for all setups
# -----------------------------------------------------------------------------
firmware        = "efi"         (1)
destination_dir = "artifacts"   (2)
disk_path       = "/dev/vda"    (3)
disk_size       = "48000"       (4)
headless        = "true"        (5)
http_dir        = "http"        (6)
root_password   = "F00bar123"   (7)
ssh_password    = "F00bar123"   (8)
target          = "server"      (9)
vg_name         = "system"      (10)

  1. Define the default firmware to be used when building a machine. Can be overridden on the command line using FIRMWARE=bios.

  2. Defines the destination or work directory where packer keeps the in progress disk files.

  3. Specify the disk device path to be used for the partitioning.

  4. Specify the disk size in megabytes.

  5. Defines if the build should open a QEMU window. For building in a CI/CD pipeline it should be set to true. Set to false for debugging.

  6. Specifies the directory where packer will point to for OS configuration files.

  7. Set the root password for system which support it. Not considered on Ubuntu hosts.

  8. The password used for logging into the machine during the post-installation phase.

  9. Specify the disk layout target. Can be overridden with the command line TARGET=pcidss.

  10. Specify the name of the LVM volume group to be used.

<distro_N.N>.pkrvars.hcl

For each OS build a file with the distro name and the release version needs to be present. E.g. for a Rocky 9.1 installation the file is called rocky_9.1.pkrvars.hcl while for Ubuntu 22.04.1 the file is ubuntu_22.04.1.pkrvars.hcl

Below is a annotated Ubuntu pkrvars file.

# -----------------------------------------------------------------------------
# Ubuntu 20.04 Packer Variable File
# -----------------------------------------------------------------------------
iso_checksum      = "file:iso/ubuntu_22.04/ubuntu-22.04.1-live-server-amd64.iso.sha256" (1)
iso_file          = "ubuntu-22.04.1-live-server-amd64.iso" (2)
iso_base_url      = "https://releases.ubuntu.com/22.04/"   (3)
name              = "ubuntu"                               (4)
ssh_username      = "ubuntu"                               (5)
version           = "22.04"                                (6)
version_minor     = "1"                                    (7)
code_name         = "jammy"                                (8)
answer_file       = ""                                     (9)
bios_boot_command = [                                      (10)
  "<enter><enter><f6><esc><wait>",
  "<bs><bs><bs><bs>",
  "autoinstall ",
  "net.ifnames=0 ",
  "biosdevname=0 ",
  "ip=dhcp ",
  "ipv6.disable=1 ",
  "ds=nocloud-net;",
  "s=http://{{ .HTTPIP }}:{{ .HTTPPort }}/%s ",
  "--- <enter>"
]
efi_boot_command  = [                                      (11)
  "c<enter><wait>",
  "linuxefi /casper/vmlinuz ",
  "quiet ",
  "autoinstall ",
  "net.ifnames=0 ",
  "biosdevname=0 ",
  "ip=dhcp ",
  "ipv6.disable=1 ",
  "ds=nocloud-net\\;",
  "s=http://{{ .HTTPIP }}:{{ .HTTPPort }}/%s ",
  "---- ",
  "; inst.stage2=hd:LABEL=%s ",
  "<enter><wait2>",
  "initrdefi /casper/initrd<enter><wait3>",
  "boot<enter><wait>"
]

  1. Location of the SHA256 sum file matching the defined IOS file.

  2. Base name of the ISO file required for the installation.

  3. Base URL where the ISO file can be downloaded at.

  4. Distribution name.

  5. User name used during the post installation login.

  6. Distribution version. Generally a single digit with the exception of Ubuntu releases.

  7. Minor version of the release. Generally a single digit with the exception of Debian releases.

  8. Code name of the release. Only used for Ubuntu and Debian releases.

  9. Answer file defaults to an empty string for subiquity based installers. On Red Hat and derivatives this is set to kickstart.cfg.

  10. Commands simulated during installation of a BIOS build. Only required for non Red Hat based distributions.

  11. Commands simulated during installation of a EFI build. Only required for non Red Hat based distributions.

Template Files

For each distribution there is a sub directory present under the templates directory. Depending on the distributions deployment method the files stored therein vary. For Red Hat based distributions and their derivatives the only file found is called kickstart.cfg.erb. Subiquity installers used in newer Ubuntu hosts contain two files user-data.erb and meta-data.erb. Below is a primer of the ERB language and the variable present when filling placeholders.

Variable Scope

The Rakefile contains a parsing module which is putting all the variables found in {common_auto_pkrvars_hcl} and OS specific files such as say ubuntu_22.04.1.pkrvars.hcl. The variable are stored in a hash called config where the key is the variable name.

E.g. ssh_username = "ubuntu" from a pkrvars.hcl file can be expanded via config['ssh_username'] in the template.

kickstart.cfg

TBD

user-data

The user-data file is used by subiquity to install the Ubuntu operating system fully automatically. Although some of the syntax is shared with cloud-init some differences exist.

---
#cloud-config (1)
autoinstall:
  version: 1
  source:
    id: ubuntu-server-minimal
  identity: (2)
    hostname: <%= config['code_name'] %>
    password: <%= PasswordFactory.sha512(config['ssh_password']).hashed %>
    realname: ubuntu
    username: <%= config['ssh_username'] %>
  keyboard:
    layout: en
    variant: us
  locale: en_US.UTF8
  refresh-installer:
    update: no
  network:
    ethernets:
      eth0:
        dhcp4: true
        dhcp-identifier: mac
    version: 2
  ssh:
    allow-pw: true
    install-server: true
  storage: (3)
    version: 1
    swap:
      size: 0
    config:
    # Label
    # partitioning
    # LVM VG
    # LVM LV
    # FS
    # Mount

  late-commands: (4)
    - "test -b <%= config['disk_path'] %>4 && parted <%= config['disk_path'] %> resizepart 4 100% || :"
    - sed -i 's/^#*\(send dhcp-client-identifier\).*$/\1 = hardware;/' /target/etc/dhcp/dhclient.conf

  packages: (5)
    - bc
    - curl
    - wget
    - openssh-server
    - qemu-guest-agent
    - eject
  updates: security

  1. The file must start with the #cloud-config line!

  2. Mandatory identiy section defaults to the ubuntu users.

  3. Storage section shortend for a better overview. See actual files under template for more information.

  4. Late command / shell scriptlets executed at the end of the installation.

  5. Package to be installed additionally to the defined tasksel base instalation.

preeseed.cfg

TBD