102.6: Linux as a Virtualization Guest

Linux as a Virtualization Guest: A Comprehensive Guide #

Virtualization and cloud computing have revolutionized the way we use and deploy operating systems, including Linux. In this tutorial, we’ll explore the key aspects of using Linux as a virtualization guest, covering both virtual machines and containers. We’ll also delve into practical examples to help solidify these concepts.

Understanding Virtual Machines and Containers #

Virtual Machines (VMs) #

A virtual machine (VM) is a software emulation of a physical computer. VMs run on a hypervisor, which can be either Type 1 (bare-metal, running directly on the hardware) or Type 2 (hosted, running on top of a host operating system). VMs provide complete isolation from the host system, which includes dedicated CPU, memory, and storage resources.

Common Elements in IaaS Cloud:

  • Computing Instances: Virtual CPUs, memory allocation.
  • Block Storage: Persistent storage devices that can be attached to instances.
  • Networking: Virtual network interfaces, IP addresses, and security groups.

Example of creating a VM using virt-install:

sudo virt-install \
  --name ubuntu-vm \
  --ram 2048 \
  --disk path=/var/lib/libvirt/images/ubuntu-vm.qcow2,size=10 \
  --vcpus 2 \
  --os-type linux \
  --os-variant ubuntu20.04 \
  --network bridge=virbr0 \
  --graphics none \
  --console pty,target_type=serial \
  --location 'http://archive.ubuntu.com/ubuntu/dists/focal/main/installer-amd64/' \
  --extra-args 'console=ttyS0,115200n8 serial'

Linux Containers #

Containers are lightweight alternatives to VMs that share the host system’s kernel while maintaining isolated user spaces. They are more efficient than VMs in terms of resource usage and startup time. Containers can be managed using tools like Docker and Kubernetes.

Example of creating a container using Docker:

# Pull an Ubuntu image
docker pull ubuntu:latest

# Run a container
docker run -it --name my-ubuntu-container ubuntu:latest /bin/bash

Unique Properties of Cloned Linux Systems #

When cloning a Linux system or using it as a template, certain properties must be changed to avoid conflicts and ensure proper functionality.

  1. SSH Host Keys:

    • SSH keys are used to identify the server. Cloned systems must generate new SSH keys to avoid security issues.
    sudo rm /etc/ssh/ssh_host_*
sudo dpkg-reconfigure openssh-server

  2. D-Bus Machine ID:

    • The D-Bus machine ID must be unique to each system.
    sudo rm /etc/machine-id
sudo systemd-machine-id-setup

Using System Images for Deployment #

System images are snapshots of configured and ready-to-use systems that can be deployed as VMs, cloud instances, or containers. Tools like Packer can be used to create such images.

Example of a Packer configuration file for creating an Ubuntu image:

{
  "builders": [{
    "type": "virtualbox-iso",
    "iso_url": "http://releases.ubuntu.com/20.04/ubuntu-20.04-live-server-amd64.iso",
    "iso_checksum": "sha256:7d4b6b5b3c823e0cb243587f57c6c8b4c982fbf0b8ab3c9e6c2b5beef3dd6824",
    "ssh_username": "ubuntu",
    "ssh_password": "password",
    "ssh_wait_timeout": "20m",
    "shutdown_command": "echo 'ubuntu' | sudo -S shutdown -P now"
  }]
}

Linux Extensions for Virtualization Integration #

Linux provides various extensions and tools to enhance its integration with virtualization platforms.

  1. Guest Drivers:

    • These are specialized drivers that improve the performance and functionality of VMs.
    • Example: virtio drivers for KVM/QEMU.

  2. Cloud-Init:

    • A tool for initializing cloud instances with user data, such as setting up users, SSH keys, and more.
    # Example cloud-init user data file
#cloud-config
users:
  - name: ubuntu
    ssh-authorized-keys:
      - ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAq...

Practical Examples #

Creating a Virtual Machine with KVM #

sudo apt-get install qemu-kvm libvirt-daemon-system libvirt-clients bridge-utils virt-manager
sudo virt-install \
  --name my-kvm-vm \
  --ram 2048 \
  --disk path=/var/lib/libvirt/images/my-kvm-vm.qcow2,size=10 \
  --vcpus 2 \
  --os-type linux \
  --os-variant ubuntu20.04 \
  --network bridge=virbr0 \
  --graphics none \
  --console pty,target_type=serial \
  --location 'http://archive.ubuntu.com/ubuntu/dists/focal/main/installer-amd64/' \
  --extra-args 'console=ttyS0,115200n8 serial'

Creating a Docker Container #

# Pull an Ubuntu image
docker pull ubuntu:latest

# Run a container
docker run -it --name my-ubuntu-container ubuntu:latest /bin/bash

Using Cloud-Init to Configure a VM #

# Create a cloud-init configuration file
cat <<EOF > cloud-init.cfg
#cloud-config
users:
  - name: ubuntu
    ssh-authorized-keys:
      - ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAq...
EOF

# Launch a VM with cloud-init configuration
sudo virt-install \
  --name cloud-init-vm \
  --ram 2048 \
  --disk path=/var/lib/libvirt/images/cloud-init-vm.qcow2,size=10 \
  --vcpus 2 \
  --os-type linux \
  --os-variant ubuntu20.04 \
  --network bridge=virbr0 \
  --graphics none \
  --console pty,target_type=serial \
  --location 'http://archive.ubuntu.com/ubuntu/dists/focal/main/installer-amd64/' \
  --cloud-init user-data=cloud-init.cfg

Conclusion #

Understanding the role of Linux as a virtualization guest is crucial for modern IT environments. By mastering the concepts of virtual machines, containers, and cloud integration, you’ll be well-equipped to manage and deploy Linux systems in any virtualized infrastructure. Whether using VMs or containers, ensure that cloned systems are properly reconfigured to maintain security and functionality. Happy virtualizing!