Creating custom images

Users can create custom images of various operating systems that can be used within an OpenStack environment. Tools such as cloud-init can be installed in the image to provide a method of bootstrapping an instance once it has been deployed.

Note

The use of cloud-init is beyond the scope of this book. More information can be found at https://cloud-init.io.

Getting ready

To begin, ensure that you are using an operating system that is not the OpenStack environment used throughout this book. Software packages and libraries needed to create images may conflict with the software currently installed, and could result in a broken environment. In this example, we will use a virtual machine configured with Ubuntu 16.04 LTS to create a custom CentOS 7 image.

Note

Configuring a virtual machine with the Ubuntu 16.04 LTS operating system is beyond the scope of this book. A physical server can be used in lieu of a virtual machine, if necessary.

The following packages are prerequisites for the host building of the image:

  • qemu-kvm
  • libvirt-bin
  • virt-manager

Using apt, install the packages with the following commands:

sudo apt update
sudo apt install qemu-kvm libvirt-bin virt-manager

How to do it…

Carry out the following steps within the virtual machine to create a custom image:

  1. Change to your home directory and create a kickstart file named ks.cfg with the following contents:
    cd ~/ 
install
text
url --url http://mirror.rackspace.com/CentOS/7/os/x86_64/
lang en_US.UTF-8
keyboard us
network --onboot yes --bootproto dhcp --noipv6
timezone --utc America/Chicago
zerombr
clearpart --all --initlabel
bootloader --location=mbr --append="crashkernel=auto"
part / --fstype=ext4 --size=1024 --grow
authconfig --enableshadow --passalgo=sha512
rootpw openstack
firewall --disable
selinux --disabled
skipx
shutdown
%packages
@core
openssh-server
openssh-clients
wget
curl
git
man
vim
ntp
%end
%post
%end
  2. Create an empty 10 GB virtual disk to be used by the CentOS virtual machine:
    sudo qemu-img create -f qcow2 
/var/lib/libvirt/images/centos-7.qcow2 10G
  3. Execute the following commands to initiate an unattended installation of the CentOS operating system:
    sudo virt-install --virt-type qemu 
--name centos-7 
--ram 2048 
--location="http://mirror.rackspace.com/CentOS/7/os/x86_64/" 
--disk /var/lib/libvirt/images/centos-7.qcow2,format=qcow2 
--network network=default 
--graphics vnc,listen=0.0.0.0 
--noautoconsole 
--os-type=linux 
--os-variant=centos7.0 
--initrd-inject ks.cfg 
--rng /dev/random 
--extra-args="inst.ks=file:/ks.cfg console=ttyS0,115200"

    Note

    If the installation is being performed inside a virtual machine using nested virtualization, you may need to change virt-type to qemu from kvm for the machine to start properly. Use kvm for better performance if the image is being built without nested virtualization.

    The output returned should resemble the following:

    Starting install...
Retrieving file vmlinuz...                  | 5.1 MB  00:00:01
Retrieving file initrd.img...               |  41 MB  00:00:07
Allocating 'centos-7.0-vm.img'              | 5.0 GB  00:00:00
Creating domain...                          |    0 B  00:00:00
Domain installation still in progress. You can reconnect to
the console to complete the installation process.

    From the host machine, console to the newly-created CentOS virtual machine and log in as the root user with the openstack password. To escape from the console session, press Ctrl + ]:

    virsh console centos-7

    To refresh the console, press the Enter key. The output will resemble the following:

    How to do it…

    The guest should be in the process of booting, and a live console log will be displayed. The installation process is automated and could take a while depending on the resources available to the host performing the build.

    When the installation is complete, the output will resemble the following:

    [  OK  ] Reached target Shutdown.
dracut Warning: Killing all remaining processes
Powering off.
[ 3388.611074] Power down.

    The console session should end, and you will be returned to a prompt on the host.

  4. Start the VM with the following command:
    sudo virsh start centos-7

    From the host machine, console to the CentOS virtual machine and log in as the root user with the openstack password. To escape from the console session, press Ctrl + ]:

    virsh console centos-7

    To refresh the console, press the Enter key. The output will resemble the following:

    Connected to domain centos-7
Escape character is ^]

CentOS Linux 7 (Core)
Kernel 3.10.0-693.el7.x86_64 on an x86_64

localhost login: root
Password:
Last login: Wed Aug 30 09:02:14 on tty1
[root@localhost ~]#
  5. In the guest, install the epel-release and cloud-init packages with the following commands:
    yum -y install epel-release
yum -y install cloud-init cloud-utils cloud-utils-growpart
  6. Using a text editor, replace the guest's cloud.cfg file at /etc/cloud/cloud.cfg with the following contents:
    users:
- default

disable_root: 1
ssh_pwauth:   0

locale_configfile: /etc/sysconfig/i18n
mount_default_fields: [~, ~, 'auto', 'defaults,nofail', '0', '2']
resize_rootfs_tmp: /dev
ssh_deletekeys:   0

ssh_genkeytypes:  ~
syslog_fix_perms: ~

cloud_init_modules:
- bootcmd
- write-files
- resizefs
- set_hostname
- update_hostname
- update_etc_hosts
- rsyslog
- users-groups
- ssh

cloud_config_modules:
- mounts
- locale
- set-passwords
- timezone
- puppet
- chef
- salt-minion
- mcollective
- disable-ec2-metadata
- runcmd

cloud_final_modules:
- rightscale_userdata
- scripts-per-once
- scripts-per-boot
- scripts-per-instance
- scripts-user
- ssh-authkey-fingerprints
- keys-to-console
- phone-home
- final-message

system_info:
 distro: rhel
 default_user:
   name: centos
   lock_passwd: True
   shell: /bin/bash
   sudo: ["ALL=(ALL) NOPASSWD: ALL"]
 paths:
   cloud_dir: /var/lib/cloud
   templates_dir: /etc/cloud/templates
 ssh_svcname: sshd

    Note

    The contents of cloud.cfg are constructed in YAML, and are interpreted by cloud-init upon startup. In this example, the default username used to access the instance is centos and no password is set. Instead, an SSH key must be used and will be pushed to the instance via the OpenStack metadata service. Refer to Chapter 5, Nova – OpenStack Compute, for more information.

  7. Ensure that the guest can communicate with the metadata service with the following command:
    echo "NOZEROCONF=yes" >> /etc/sysconfig/network
  8. Remove persistent rules with the following command:
    rm -rf /etc/udev/rules.d/70-persistent-net.rules
  9. Remove machine-specific MAC address and UUID. Edit the /etc/sysconfig/network-scripts/ifcfg-eth0 file and remove lines starting with HWADDR and UUID:
    sed -i '/HWADDR/d' /etc/sysconfig/network-scripts/ifcfg-eth0
sed -i '/UUID/d' /etc/sysconfig/network-scripts/ifcfg-eth0
  10. After making the changes, ensure that the interface configuration file resembles the following:
    NAME="eth0"
ONBOOT="yes"
NETBOOT="yes"
IPV6INIT="no"
BOOTPROTO="dhcp"
TYPE="Ethernet"
DEFROUTE="yes"
PEERDNS="yes"
PEERROUTES="yes"
IPV4_FAILURE_FATAL="no"

    Note

    If you need IPv6 support, modify the interface file accordingly to ensure that instances using the image can procure their IPv6 address via DHCPv6 or SLAAC.

  11. Clean up various files and directories using the following commands:
    yum clean all
rm -rf /var/log/*
rm -rf /tmp/*
history -c
  12. From within the guest, cleanly shutdown the guest using the following command:
    shutdown -h now

    Once the guest is shutdown, the console session should end and you will be returned to a prompt on the host. Transfer the disk located at /var/lib/libvirt/images/centos-7.qcow2 to your home directory, where it can be transferred out of the host and onto a client, where the OpenStack command-line utility is installed. Using the OpenStack client, upload the image to the OpenStack image repository:

    openstack image create MY_CENTOS_IMAGE 
--disk-format qcow2 
--file ~/centos-7.qcow2

    The output should resemble the following:

    How to do it…

    For more information on building custom images, visit https://docs.openstack.org/image-guide/create-images-manually.html.

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