Tool support for image creation

Tool support for image creation

There are several tools that are designed to automate image creation.

Diskimage-builder

Diskimage-builder is an automated disk image creation tool that supports a variety of distributions and architectures. Diskimage-builder (DIB) can build images for Fedora, Red Hat Enterprise Linux, Ubuntu, Debian, CentOS, and openSUSE. DIB is organized in a series of elements that build on top of each other to create specific images.

To build an image, call the following script:

# disk-image-create ubuntu vm

This example creates a generic, bootable Ubuntu image of the latest release.

Further customization could be accomplished by setting environment variables or adding elements to the command-line:

# disk-image-create -a armhf ubuntu vm

This example creates the image as before, but for arm architecture. More elements are available in the git source directory and documented in the diskimage-builder elements documentation.

Oz

Oz is a command-line tool that automates the process of creating a virtual machine image file. Oz is a Python app that interacts with KVM to step through the process of installing a virtual machine.

It uses a predefined set of kickstart (Red Hat-based systems) and preseed files (Debian-based systems) for operating systems that it supports, and it can also be used to create Microsoft Windows images.

A full treatment of Oz is beyond the scope of this document, but we will provide an example. You can find additional examples of Oz template files on GitHub at rcbops/oz-image-build/tree/master/templates. Here’s how you would create a CentOS 6.4 image with Oz.

Create a template file called centos64.tdl with the following contents. The only entry you will need to change is the <rootpw> contents.

<template>
  <name>centos64</name>
  <os>
    <name>CentOS-6</name>
    <version>4</version>
    <arch>x86_64</arch>
    <install type='iso'>
      <iso>http://mirror.rackspace.com/CentOS/6/isos/x86_64/CentOS-6.4-x86_64-bin-DVD1.iso</iso>
    </install>
    <rootpw>CHANGE THIS TO YOUR ROOT PASSWORD</rootpw>
  </os>
  <description>CentOS 6.4 x86_64</description>
  <repositories>
    <repository name='epel-6'>
      <url>http://download.fedoraproject.org/pub/epel/6/$basearch</url>
      <signed>no</signed>
    </repository>
  </repositories>
  <packages>
    <package name='epel-release'/>
    <package name='cloud-utils'/>
    <package name='cloud-init'/>
  </packages>
  <commands>
    <command name='update'>
yum -y update
yum clean all
sed -i '/^HWADDR/d' /etc/sysconfig/network-scripts/ifcfg-eth0
echo -n > /etc/udev/rules.d/70-persistent-net.rules
echo -n > /lib/udev/rules.d/75-persistent-net-generator.rules
    </command>
  </commands>
</template>

This Oz template specifies where to download the Centos 6.4 install ISO. Oz will use the version information to identify which kickstart file to use. In this case, it will be RHEL6.auto. It adds EPEL as a repository and install the epel-release, cloud-utils, and cloud-init packages, as specified in the packages section of the file.

After Oz completes the initial OS install using the kickstart file, it customizes the image with an update. It also removes any reference to the eth0 device that libvirt creates while Oz does the customizing, as specified in the command section of the XML file.

To run this:

# oz-install -d3 -u centos64.tdl -x centos64-libvirt.xml
  • The -d3 flag tells Oz to show status information as it runs.
  • The -u tells Oz to do the customization (install extra packages, run the commands) once it does the initial install.
  • The -x flag tells Oz what filename to use to write out a libvirt XML file (otherwise it will default to something like centos64Apr_03_2013-12:39:42).

If you leave out the -u flag, or you want to edit the file to do additional customizations, you can use the oz-customize command, using the libvirt XML file that oz-install creates. For example:

# oz-customize -d3 centos64.tdl centos64-libvirt.xml

Oz will invoke libvirt to boot the image inside of KVM, then Oz will ssh into the instance and perform the customizations.

VeeWee

VeeWee is often used to build Vagrant boxes, but it can also be used to build the KVM images.

Packer

Packer is a tool for creating machine images for multiple platforms from a single source configuration.

image-bootstrap

image-bootstrap is a command line tool that generates bootable virtual machine images with support of Arch, Debian, Gentoo, Ubuntu, and is prepared for use with OpenStack.

imagefactory

imagefactory is a newer tool designed to automate the building, converting, and uploading images to different cloud providers. It uses Oz as its back-end and includes support for OpenStack-based clouds.

KIWI

The KIWI OS image builder provides an operating system image builder for various Linux supported hardware platforms as well as for virtualization and cloud systems. It allows building of images based on openSUSE, SUSE Linux Enterprise, and Red Hat Enterprise Linux. The openSUSE Documentation explains how to use KIWI.

virt-builder

Virt-builder is a tool for quickly building new virtual machines. You can build a variety of VMs for local or cloud use, usually within a few minutes or less. Virt-builder also has many ways to customize these VMs. Everything is run from the command line and nothing requires root privileges, so automation and scripting is simple.

To build an image, call the following script:

# virt-builder fedora-23 -o image.qcow2 --format qcow2 \
  --update --selinux-relabel --size 20G

To list the operating systems available to install:

$ virt-builder --list

To import it into libvirt with virsh:

# virt-install --name fedora --ram 2048 \
  --disk path=image.qcow2,format=qcow2 --import

openstack-debian-images

openstack-debian-images is the tool Debian uses to create its official OpenStack image. It is made of a single very simple shell script that is easy to understand and modify. It supports Grub and Syslinux, BIOS or EFI, amd64 and arm64 arch.

openstack-debian-images can also be used to create a bootable image directly on a hard disk, instead of using the Debian installer.

To build an image, type this:

# build-openstack-debian-image --release stretch

More parameters can be added to further customize the image:

# build-openstack-debian-image --release stretch \
  --hook-script /root/my-hook-script.sh \
  --debootstrap-url http://ftp.fr.debian.org \
  --sources.list-mirror http://ftp.fr.debian.org \
  --login myusername \
  --extra-packages vim,emacs

The file /root/my-hook-script.sh will recieve 2 environment variable: BODI_CHROOT_PATH path where the image is mounted, and BODI_RELEASE which is the name of the Debian release that is being bootstraped. Here’s an example for customizing the motd:

# #!/bin/sh
  set -e
  echo "My message" >${BODI_CHROOT_PATH}/etc/motd

This hook script will conveniently be called at the correct moment of the build process, when everything is installed, but before unmounting the partition.

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