2014-05-16-how-to-create-a-custom-image-for-runabove.markdown

layout	title	categories	author	lang
post	Import a custom image in your RunAbove Account	Instances	NicolasLM	en

RunAbove provides the most widely used operating systems, optimized for the cloud. However sometimes you need to run a custom system. As the virtualization technology behind RunAbove is KVM it can run every operating system, 32 and 64 bits.

This guide will help you to setup a system from the installer and make it work with RunAbove. In this example, we will use a distribution that is not yet available in RunAbove: the 32 bits version of Debian Wheezy, but you can choose any other system.

Requirements:

The first step is to install, on your local machine, the qemu-kvm tools. Check your distribution repository for the proper packets to install. For example, on a Debian host it would be the packages qemu-system and qemu-utils:

apt-get install qemu-system qemu-utils

Once your host is able to run qemu/KVM virtualization you can download the installer of the system you want. Any ISO image will be fine.

Virtual drive creation:

Now you have to create the virtual drive that will handle your installed system. The qcow2 format, allows users to make big virtual disks, while keeping the file size on your host minimal. To build a 3 GB virtual drive issue the following:

qemu-img create -f qcow2 debian-7-32.qcow2 3G

Custom system installation:

You can use this shell script that runs qemu with the proper settings to install a system compatible with RunAbove.

#!/bin/bash

#### Configuration #####
#
QEMU_KVM='qemu-system-x86_64'
CPUs="cores=4,threads=1,socket=1"
RAM=1024
CLOCK_BASE="utc"
#
########################


if [ $# -lt 2 ]; then
cat <<EOF
Usage: $0 drive cdrom

    drive       Virtual drive where the system will be installed
    cdrom       ISO installer of the operating system

EOF
    exit 1
fi

bin_qemu_kvm=`which $QEMU_KVM | wc -l`
if [ "$bin_qemu_kvm" == "0" ]; then
    echo "The program $QEMU_KVM cannot be found"
    exit 1
fi

if [ ! -f "$1" ]; then
    echo "The virtual drive file $QEMU_KVM doesn't exist"
    exit 1
fi

if [ ! -f "$2" ]; then
    echo "The ISO installer $QEMU_KVM doesn't exist"
    exit 1
fi

$QEMU_KVM \
        -nodefaults \
        -drive file=$1,if=virtio,id=drive-virtiodisk0,cache=none \
        -cdrom $2 \
        -boot once=d,menu=on \
        -enable-kvm \
        -cpu host \
        -smp $CPUs \
        -m $RAM \
        -rtc base=$CLOCK_BASE,clock=host \
        -netdev user,id=usernet,net=169.254.0.0/16,hostfwd=tcp::2222-:22,hostfwd=tcp::8080-:80 \
        -device virtio-net-pci,netdev=usernet \
        -vga cirrus

The first parameter is the virtual drive and the second one is the ISO CD of the installer. Make it executable and run it:

chmod +x qemu-install
./qemu-install debian-7-32.qcow2 debian-7.5.0-i386-netinst.iso

You will see a qemu window that appears, just boot from the CD ROM and the installer will start.

Install the system so it fits your needs and once you are satisfied with the result you can shut down the virtual machine. Next time you boot the VM, it it will be running on extremely performant hardware, because now, it's time to upload it to the cloud!

Upload your custom image:

Before uploading your image to RunAbove you can use the compression feature of the qcow2 format. Compression allows users upload images faster. By issuing this command you will create a compressed copy of your system. The first parameter is the image you just built and the second is the compressed version that will be created:

qemu-img convert -c -f qcow2 -O qcow2 debian-7-32.qcow2 debian-7-32.gz.qcow2

Once you have the compressed image it is ready to be uploaded to RunAbove. This guide shows how simple it is to transfer an image to the service.

Some advice on how to build better images:

• RunAbove uses the powerful VirtIO drivers for block devices and network adapters. Those drivers are available directly in the Linux kernel.
• Windows needs additional VirtIO drivers, that you can find on the RedHat project. You have to add VirtIO drivers as a third disk and load them from the installer when it prompts you.
• You will have to expand the main drive once your instance is running. You can do it manually or launch tools that will do that for you.
• All network configuration is done by DHCP, no need to worry with that.
• Root password and your SSH key are directly injected to your instance so no need to worry either.
• You can set firewall rules from the manager, they will be interpreted before routing packets to your instance so you don't need to bother setting a firewall inside each instance.
• A web service that gives information about the instance is available from the instance itself at http://169.254.169.254. You can install tools like cloud-init that use this web service to customize the instance at boot time
• OpenStack provides many guides for creating various images.