Creating Ubuntu Template Images with Proxmox Cloud-Init

#Getting Started

I'm running a Proxmox cluster on my personal hardware.

At first, I was just grateful that VMs could be created at all. But humans are fickle creatures.

Gradually, installing Ubuntu started to feel tedious.

So, just like clicking a button in the AWS Console, I initially used cloned VMs from pre-configured setups.

But then, issues like ID conflicts and DHCP failures started piling up, making things annoying again.

While looking around for solutions, I discovered that AWS actually uses something called cloud-init for one-click installations. Today, I'm going to document what I learned about it.

#1. Download Ubuntu Cloud Image and Resize Disk

First, download the latest Jammy (22.04) image file and expand the disk size.

wget https://cloud-images.ubuntu.com/jammy/current/jammy-server-cloudimg-amd64.img
qemu-img resize jammy-server-cloudimg-amd64.img 50G

• Ubuntu's official Cloud Image comes with cloud-init pre-installed, making it ideal for automating initial setup.\
• Since the default size is small, we expand it to 50GB using the qemu-img resize command.

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#2. Create Proxmox VM

qm create 99001 --name=ubuntu-22-04 --memory=2048 --net0 virtio,bridge=vmbr1

• VM ID: 99001
• Name: ubuntu-22-04
• Memory: 2GB
• Network: VirtIO + Bridge (vmbr1)

The network bridge can be changed to vmbr0 or vmbr1 depending on your environment.

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#3. Register Cloud Image as VM Disk

qm set 99001 --virtio0 iSCSI-2T:0,import-from=/mnt/pve/NFS-AN/template/iso/jammy-server-cloudimg-amd64.img

• Connect as virtio0 disk\
• Use the import-from option to directly import the existing Cloud Image to the specified storage (iSCSI-2T)\
• During import, automatic conversion from QCOW2 to RAW occurs

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#4. Add Cloud-Init Drive

qm set 99001 --ide2 iSCSI-2T:cloudinit

• Add a Cloud-Init configuration drive to inject user metadata during initial boot\
• Commonly used to automate SSH keys, hostname, network settings, etc.

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#5. Boot and Console Configuration

qm set 99001 --boot order=virtio0
qm set 99001 --serial0 socket --vga serial0

• Set boot order to virtio0\
• Configure serial0 console to enable text-based terminal access. You can access the console via qm terminal 99001

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#6. Specify Cloud-Init User Script

qm set 99001 --cicustom "user=NFS-GS:snippets/ubuntu-init.yaml"

• Specify a custom Cloud-Init YAML file\
• The snippets/ubuntu-init.yaml file can include user, package, SSH settings, etc.

Example (ubuntu-init.yaml):

#cloud-config
package_update: true
package_upgrade: true
timezone: Asia/Seoul
packages:
  - qemu-guest-agent
  - curl
  - ca-certificates
  - sudo

users:
  - default
  - name: yangs
    gecos: Yangs Admin
    sudo: ALL=(ALL) NOPASSWD:ALL
    shell: /bin/bash
    groups: [sudo, docker]
    lock_passwd: false
    ssh_authorized_keys:
      - "ssh-rsa ..."
runcmd:
  - |
    echo "=== Setting timezone (Asia/Seoul) ==="
    timedatectl set-timezone Asia/Seoul
    echo "Current timezone: $(timedatectl show --property=Timezone --value)"

  - |
    echo "=== Installing Docker ==="
    curl -fsSL https://get.docker.com -o /tmp/get-docker.sh
    chmod +x /tmp/get-docker.sh
    sh /tmp/get-docker.sh

  - |
    echo "=== Installing Docker Compose ==="
    curl -L "https://github.com/docker/compose/releases/download/1.27.4/docker-compose-$(uname -s)-$(uname -m)" \
      -o /usr/local/bin/docker-compose
    chmod +x /usr/local/bin/docker-compose

  - |
    echo "=== Docker service configuration: auto-start and restart policy ==="
    systemctl enable docker
    mkdir -p /etc/docker
    echo '{' > /etc/docker/daemon.json
    echo '  "log-driver": "json-file",' >> /etc/docker/daemon.json
    echo '  "log-opts": {' >> /etc/docker/daemon.json
    echo '    "max-size": "50m",' >> /etc/docker/daemon.json
    echo '    "max-file": "3"' >> /etc/docker/daemon.json
    echo '  }' >> /etc/docker/daemon.json
    echo '}' >> /etc/docker/daemon.json
    systemctl daemon-reload
    systemctl restart docker
    sudo usermod -aG docker yangs || true
    echo "=== Docker configuration complete ==="


  - |
    echo "=== Enabling QEMU Guest Agent ==="
    systemctl enable qemu-guest-agent
    systemctl start qemu-guest-agent

  - |
    echo "=== Creating Prometheus Node Exporter container ==="
    sudo docker run --name=node-exporter \
      --restart=always \
      -d \
      --net="host" \
      --pid="host" \
      -v "/:/host:ro,rslave" \
      quay.io/prometheus/node-exporter:latest \
      --path.rootfs=/host || true
    echo "=== Verifying Node Exporter execution ==="
    sudo docker ps | grep node-exporter || echo "Node Exporter container creation complete"

  - |
    echo "=== Starting Ubuntu Clone initialization ==="
    set -e
    echo "[1/6] Initializing machine-id..."
    rm -f /etc/machine-id
    dbus-uuidgen --ensure=/etc/machine-id
    systemd-machine-id-setup

    echo "[2/6] Initializing SSH host keys..."
    rm -f /etc/ssh/ssh_host_*
    dpkg-reconfigure -f noninteractive openssh-server


    echo "[4/6] Clearing netplan / udev network cache..."
    rm -f /etc/udev/rules.d/70-persistent-net.rules
    rm -f /etc/netplan/*.bak

    echo "[5/6] Initializing hostname..."
    new_hostname="ubuntu-$(openssl rand -hex 3)"
    hostnamectl set-hostname "$new_hostname"
    echo "New hostname: $new_hostname"

    echo "[6/6] Cleaning up logs and cache..."
    rm -rf /var/log/*
    rm -rf /tmp/*
    rm -rf /var/tmp/*

    echo "=== Initialization complete ==="
    echo "Please reboot now with 'sudo reboot'."

power_state:
  mode: reboot
  timeout: 30
  message: "Automatic reboot after Ubuntu initialization is complete."

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#7. Convert to Template

qm template 99001

• Convert the configured VM to a template\
• You can then quickly create multiple instances using the qm clone command