Ubuntu 22.04/20.04 Automated Provisioning: Cloud-init & Subiquity

Unlike traditional CentOS Kickstart, modern Ubuntu Server (20.04+) utilizes the Autoinstall mechanism based on Cloud-init. This document details how to set up an automated provisioning server supporting both UEFI and Legacy boot modes.

1. Environment Preparation (Server Side)

Assume PXE Server IP is 192.168.243.128.

1.1 Install Basic Services

apt update && apt install -y tftpd-hpa apache2 isc-dhcp-server syslinux pxelinux

1.2 Configure HTTP & TFTP

We use Apache2 to host the ISO image and Cloud-init configuration (user-data).

Configure Apache2 to serve TFTP directory:

cat > /etc/apache2/conf-available/tftp.conf <<EOF
<Directory /var/lib/tftpboot>
        Options +FollowSymLinks +Indexes
        Require all granted
</Directory>
Alias /tftp /var/lib/tftpboot
EOF

# Enable and Reload
a2enconf tftp
systemctl reload apache2

Configure TFTP Service: Edit /etc/default/tftpd-hpa:

TFTP_USERNAME="tftp"
TFTP_DIRECTORY="/var/lib/tftpboot"
TFTP_ADDRESS=":69"
TFTP_OPTIONS="--secure"

Restart: systemctl restart tftpd-hpa

1.3 Prepare Kernel & Image

Mount the Ubuntu Server ISO and extract boot files.

# 1. Mount ISO
mount -o loop ubuntu-22.04.4-live-server-amd64.iso /mnt

# 2. Copy Kernel (vmlinuz) and Initrd
cp /mnt/casper/vmlinuz /var/lib/tftpboot/
cp /mnt/casper/initrd /var/lib/tftpboot/

# 3. Copy full ISO to HTTP directory for client download
cp ubuntu-22.04.4-live-server-amd64.iso /var/lib/tftpboot/

1.4 Configure DHCP

Edit /etc/dhcp/dhcpd.conf:

subnet 192.168.243.0 netmask 255.255.255.0 {
  range 192.168.243.11 192.168.243.100;
  option routers 192.168.243.1;
  next-server 192.168.243.128; # PXE Server IP
  
  filename "pxelinux.0"; 
  # Note: For dual UEFI/Legacy support, use 'class' matching in DHCP config.
}

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2. Prepare Autoinstall Config (User-Data)

This is the core of automation. You can reuse the /var/log/installer/autoinstall-user-data generated after a manual installation.

cp /var/log/installer/autoinstall-user-data /var/lib/tftpboot/user-data

Key Modification: Set root partition size to -1 to use all available space.

# user-data snippet
storage:
  config:
    - type: partition
      id: partition-2
      size: -1  # Expand to fill disk

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3. UEFI Boot Configuration

UEFI requires grubnetx64.efi.signed.

3.1 Get Bootloader

wget http://archive.ubuntu.com/ubuntu/dists/focal/main/uefi/grub2-amd64/current/grubnetx64.efi.signed -O /var/lib/tftpboot/pxelinux.0

3.2 Configure GRUB Menu

Create /var/lib/tftpboot/grub/grub.cfg:

default=autoinstall
timeout=30
menuentry "Ubuntu 22.04 Autoinstall (UEFI)" {
    set gfxpayload=keep
    # ds=nocloud-net;s=... specifies the directory containing user-data
    linux /vmlinuz ip=dhcp url=http://192.168.243.128/tftp/ubuntu-22.04.4-live-server-amd64.iso autoinstall ds=nocloud-net;s=http://192.168.243.128/tftp/
    initrd /initrd
}

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4. Legacy BIOS Boot Configuration

4.1 Prepare Syslinux Components

# Copy Syslinux modules
cp /usr/lib/syslinux/modules/bios/{libcom32.c32,ldlinux.c32,libutil.c32,menu.c32,vesamenu.c32} /var/lib/tftpboot/
cp /usr/lib/PXELINUX/lpxelinux.0 /var/lib/tftpboot/

4.2 Configure Boot Menu

Create /var/lib/tftpboot/pxelinux.cfg/default:

default vesamenu.c32
timeout 60
label autoinstall
  menu label ^Autoinstall Ubuntu 22.04 (Legacy)
  kernel /vmlinuz
  append initrd=/initrd ip=dhcp url=http://192.168.243.128/tftp/ubuntu-22.04.4-live-server-amd64.iso autoinstall ds=nocloud-net;s=http://192.168.243.128/tftp/

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5. Offline Package Acquisition

If the server has no internet access, download packages on a connected VM.

5.1 Download Only

# Download package and dependencies
apt-get download $(apt-cache depends --recurse --no-recommends --no-suggests --no-conflicts --no-breaks --no-replaces --no-enhances tftpd-hpa | grep "^\w")

5.2 Install Offline

Transfer .deb files to the offline server:

dpkg -i *.deb

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Summary

Automating Ubuntu installation relies on Cloud-init, which is more flexible but network-dependent (requires HTTP download of the full ISO) compared to Kickstart. Ensure your user-data YAML syntax is correct to avoid installation failures.