cloud-init is a widely used tool in Linux for automatically configuring virtual machines or cloud instances at first boot. It is commonly used by cloud providers like AWS, Azure, Google Cloud, DigitalOcean, and OpenStack to perform initialization tasks when a new instance is launched.

🔧 What It Does

cloud-init allows automatic configuration of things like:

  • Setting the hostname
  • Creating users and setting SSH keys
  • Installing packages
  • Running shell scripts
  • Attaching volumes or configuring networks
  • Writing files (e.g., configuration files)

📦 How It Works

  1. Data Sources: It fetches instance metadata and configuration from sources like:

    • EC2 metadata service
    • ConfigDrive (used by OpenStack)
    • NoCloud (for local testing with ISO or disk)

  2. User-Data Script: You can pass a cloud-init script (YAML or shell) when you create an instance. This is called user data.

  3. Execution Stages:

    • init: Setup and detect data source
    • config: Apply configuration (users, files, etc.)
    • final: Run custom scripts

📄 Example cloud-config (YAML):

#cloud-config
hostname: my-server
users:
  - name: vitalie
    sudo: ALL=(ALL) NOPASSWD:ALL
    ssh-authorized-keys:
      - ssh-rsa AAAAB3...

packages:
  - htop
  - git

runcmd:
  - echo "Welcome to cloud-init!" > /etc/motd

🛠 Common Use Cases

  • Automating VM provisioning in CI/CD
  • Creating reproducible server images
  • Initializing Kubernetes nodes
  • Bootstrapping cloud infrastructure

Great — since you’re using Proxmox, here’s how cloud-init works in that context:

🖥️ What is cloud-init in Proxmox?

In Proxmox VE, cloud-init is used to automatically configure virtual machines (VMs) (not containers) during their first boot, especially when you’re cloning from a cloud-init enabled template.

It is ideal for creating dynamic VMs with unique settings, such as IP addresses, SSH keys, hostnames, and user credentials, from a single template.

✅ Typical Use Cases in Proxmox

  • Automatically assign a static IP, DNS, and hostname
  • Inject SSH public keys for login
  • Set user passwords or disable password logins
  • Run first-boot scripts (like package installs)

🧱 How It Works in Proxmox

  1. Create a Cloud-Init Ready VM Template

    • Use a cloud-ready Linux image (e.g., Ubuntu Cloud, CentOS Cloud, Debian Cloud).
    • Add a cloud-init drive via the Proxmox GUI or CLI.

  2. Convert the VM to a Template

    qm template <vmid>

  3. Clone New VMs from the Template

    qm clone <template-id> <new-vm-id> --name new-vm-name

  4. Configure Cloud-Init Parameters In the Proxmox UI (under the VM → Cloud-Init tab), or via CLI:

    qm set <vmid> --ciuser vitalie --sshkey ~/.ssh/id_rsa.pub \
  --ipconfig0 ip=192.168.1.100/24,gw=192.168.1.1

  5. Start the VM

    qm start <vmid>

    cloud-init runs on boot and configures the VM according to your settings.

🔧 Requirements

  • The guest OS must have cloud-init pre-installed.
  • The VM should use VirtIO disk/network and serial console (for easier debug).
  • The Proxmox VM must have a cloud-init drive added (scsciX: cloudinit).

🔍 Debugging Tips

  • Log into the VM and check logs:

    sudo journalctl -u cloud-init
sudo cloud-init status
sudo cloud-init analyze

Here’s a step-by-step guide to create a cloud-init enabled Ubuntu 22.04 template on Proxmox, which you can use to clone VMs with unique config (IP, hostname, SSH keys, etc.):

🧰 Prerequisites

  • Proxmox VE installed
  • SSH access or console access to Proxmox host
  • A Linux Bridge network in Proxmox (e.g. vmbr0)

✅ Step-by-Step: Ubuntu 22.04 Cloud-Init Template

1. Download Ubuntu Cloud Image

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

You can rename it if you prefer:

mv jammy-server-cloudimg-amd64.img ubuntu-22.04-cloudinit.img

2. Create a New VM in Proxmox

VMID=9000
qm create $VMID --name ubuntu-2204-cloudinit \
  --memory 2048 --cores 2 --net0 virtio,bridge=vmbr0 \
  --ostype l26 --serial0 socket --vga serial0

serial0 is important for cloud-init console access.

3. Import the Cloud Image Disk

qm importdisk $VMID ubuntu-22.04-cloudinit.img local-lvm

Replace local-lvm with your storage name if different.

4. Attach the Disk to the VM

qm set $VMID --scsihw virtio-scsi-pci --scsi0 local-lvm:vm-$VMID-disk-0
qm set $VMID --boot c --bootdisk scsi0

5. Add Cloud-Init Drive

qm set $VMID --ide2 local-lvm:cloudinit

Also set a default serial console:

qm set $VMID --serial0 socket --vga serial0

6. Convert to a Template

qm template $VMID

Now this VM is a reusable cloud-init template.

🚀 Deploying from the Template

1. Clone the Template

qm clone 9000 101 --name ubuntu-vm-01

2. Set Cloud-Init Options

qm set 101 --ciuser vitalie --sshkey ~/.ssh/id_rsa.pub
qm set 101 --ipconfig0 ip=192.168.1.101/24,gw=192.168.1.1

You can also do this from Proxmox UI: select the VM → Cloud-Init tab.

3. Start the VM

qm start 101

✅ VM will now:

  • Set hostname automatically
  • Use static IP or DHCP
  • Inject your SSH key
  • Set login user (e.g., vitalie)

🧪 Test Login

ssh [email protected]

🛠️ Useful Commands Inside VM

# Check cloud-init status
cloud-init status

# View logs
journalctl -u cloud-init

# Analyze boot performance
cloud-init analyze