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RancherVM Images

RancherVM images are standard KVM images bundled in Docker images. We recommend you use compressed qcow2 images. Any format that can serve as a QEMU base image will also work, but compressed qcow2 images are preferred due to its small size.

Build VM Images

There are many tools you can use to build VM images. One tool we particularly like is virt-manager. It allows you to configure virtio devices and install operating systems from bootable ISO files.

On Ubuntu (and perhaps on other Linux distributions as well) virt-manager places the resulting qcow2 image in a directory called /var/lib/libvirt/images/. You need to be root to read the qcow2 images in that directory.

Compress VM Images

After you have installed the operating system in a qcow2 file and created a file like myos.img, run the qemu-img convert command to compress the image. For example:

qemu-img convert -O qcow2 -c myos.img myos.gz.img

Image compression can lead to over 50% size reduction.

Build VM Container Images

You can follow the example of one of the VM images included with RancherVM to build your own VM image. The following, for example, is the Dockerfile for building RancherOS VM:

FROM rancher/vm-base:0.0.1
COPY rancheros-0.3.0-gz.img /base_image/rancheros-0.3.0-gz.img
CMD ["-m 512m"]

All VM containers must use rancher/vm-base as the base image. You can give the qcow2 image any name you want. The qcow2 image must be copied into the /base_image directory. There must be exactly one image file in that directory.

Note that the -m 512 option is passed to KVM. The CMD commands or any command line options following the Docker image argument in docker run are passed verbatim to KVM.

Virtio Drivers

Preferrably, the images are built to work with KVM virto drivers. It is possible to configure your VM container to work with other storage and network drivers as well. RancherVM uses the following KVM command line options to configure storage and networking devices. You can redefine one or both of these environment valuables (in Dockerfile or docker run command line) to the device of your choice.

KVM_BLK_OPTS="-drive file=\$KVM_IMAGE,if=none,id=drive-disk0,format=qcow2 -device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x6,drive=drive-disk0,id=virtio-disk0,bootindex=1"
KVM_NET_OPTS="-netdev bridge,br=\$BRIDGE_IFACE,id=net0 -device virtio-net-pci,netdev=net0,mac=\$MAC"

Note that RancherVM scripts will substitute in the right value for $KVM_IMAGE, $BRIDGE_IFACE, and $MAC.

  1. Place $KVM_IMAGE in the block device option where the qcow2 image file is specified.
  2. Make sure KVM networking is configured as bridge mode and the virtual NIC is bridged to $BRIDGE_IFACE.
  3. Make sure the MAC address of the virtual NIC is set to $MAC.

Do not mess with these valriables. Do not remove the \ before $ character. Place these variables exactly where they should be. If you do not know where they should go, you have probably messed up the command line options.

You can use virt-manager to figure out what command line options you need to use should you decide to customize KVM_BLK_OPTS and KVM_NET_OPTS. Just configure what you want in virt-manager, start the VM, and type ps -ef | grep kvm to see what command line options virt-manager has generated.

Build Windows VM Images

Linux distributions generally support virtio out of the box. You need to take special steps to install virtio drivers for Windows. This video explains how to build a Windows image for RancherVM.

Build Images using Emulated Drivers

Some operating systems do not support virtio drivers. In the image/android-x86 directory, you can find the instructions to build a KVM image using the vanilla emulated drivers. Emulated drivers are less efficient, but they work with many more operating systems.