2. First contact

Simple bootstrapping with the Rocky Linux 10 QCOW2 image

In the previous chapter, we covered the fundamental concepts of cloud-init. Now, it is time to move from theory to practice. This chapter is your first hands-on mission: you will take the official Rocky Linux 10 Generic Cloud image, provide it with a simple set of instructions, and watch it configure itself on first boot.

1. Prepping the lab environment

Before we can boot our first instance, we need to prepare our local lab environment. For these exercises, we will simulate a cloud environment using standard Linux virtualization tools.

Prerequisites: host tools

Ensure you have the following tools installed on your host machine. On a Rocky Linux host, you can install them with dnf:

sudo dnf install -y libvirt qemu-kvm virt-install genisoimage

• Virtualization Hypervisor: A tool like KVM/QEMU or VirtualBox.
• virt-install: A command-line utility for provisioning new virtual machines.
• genisoimage (or mkisofs): A tool to create an ISO9660 filesystem.

The QCOW2 image

If you have not already, download the official Rocky Linux 10 Generic Cloud image.

curl -L -o Rocky-10-GenericCloud.qcow2 \
https://dl.rockylinux.org/pub/rocky/10/images/x86_64/Rocky-10-GenericCloud-Base.latest.x86_64.qcow2

To preserve the original, create a working copy of the image for your VM.

cp Rocky-10-GenericCloud.qcow2 first-boot-vm.qcow2

Save disk space with backing files

A full copy of the image can be large. To save disk space, you can create a linked clone that uses the original image as a backing file. This creates a much smaller qcow2 file that only stores the differences from the original.

qemu-img create -f qcow2 -F qcow2 \
-b Rocky-10-GenericCloud.qcow2 first-boot-vm.qcow2

2. Method 1: The NoCloud datasource (ISO)

One of the most common ways to provide data to cloud-init in a local environment is the NoCloud datasource. This method requires packaging your configuration files into a virtual CD-ROM (an ISO file) that cloud-init will automatically detect and read on boot.

Creating the configuration files

1. Create a directory for your configuration files:

   mkdir cloud-init-data
   

2. Create the user-data file: This file is your primary instruction set. We will use a cat heredoc to create it.

   cat <<EOF > cloud-init-data/user-data
   #cloud-config
   hostname: cloud-rockstar-01
   runcmd:
     - [ sh, -c, "echo 'Hello from the cloud-init Final Stage!' > /root/boot_done.txt" ]
   EOF
   

3. Create the meta-data file: This file provides context about the instance. The instance-id is particularly important, as cloud-init uses it to determine if it has run on this instance before. Changing the ID will cause cloud-init to run again.

   cat <<EOF > cloud-init-data/meta-data
   {
     "instance-id": "i-first-boot-01",
     "local-hostname": "cloud-rockstar-01"
   }
   EOF
   

4. Generate the ISO: Use genisoimage to package the files into config.iso. The volume label -V cidata is the magic key that cloud-init looks for.

   genisoimage -o config.iso -V cidata -r -J cloud-init-data
   

Booting and verification

1. Launch the VM with virt-install, attaching both the VM image and the config.iso.

   virt-install --name rocky10-iso-boot \
   --memory 2048 --vcpus 2 \
   --disk path=first-boot-vm.qcow2,format=qcow2 \
   --disk path=config.iso,device=cdrom \
   --os-variant rockylinux10 \
   --import --noautoconsole
   

2. Find the IP and connect via SSH. The default user is rocky.

   virsh domifaddr rocky10-iso-boot
   ssh rocky@<IP_ADDRESS>
   

   Secure logins with SSH keys

   Connecting with a default user is convenient for a quick lab test, but it is not a secure practice. In the next chapter, we will explore how to use cloud-init to automatically inject your SSH public key, allowing for secure, passwordless logins.

3. Verify the changes: Check the hostname and the file created by runcmd.

   hostname
   sudo cat /root/boot_done.txt
   

3. Method 2: Direct injection with virt-install

Creating an ISO is a reliable method, but for users of libvirt and virt-install, there is a much simpler way. The --cloud-init flag allows you to pass user-data directly, letting virt-install handle the creation of the datasource automatically.

Simplified user-data

Create a simple user-data.yml file. You can even add the SSH key preemptively.

cat <<EOF > user-data.yml
#cloud-config
users:
  - name: rocky
    ssh_authorized_keys:
      - <YOUR_SSH_PUBLIC_KEY>
EOF

Booting and verification

1. Launch the VM using the --cloud-init flag. Notice we can set the hostname here directly.

   virt-install --name rocky10-direct-boot \
   --memory 2048 --vcpus 2 \
   --disk path=first-boot-vm.qcow2,format=qcow2 \
   --cloud-init user-data=user-data.yml,hostname=cloud-rockstar-02 \
   --os-variant rockylinux10 \
   --import --noautoconsole
   

2. Find the IP and connect. If you added your SSH key, you should be able to connect without a password.

3. Verify the hostname. It should be cloud-rockstar-02.

This direct method is often faster and more convenient for local development and testing with libvirt.

Author: Wale Soyinka