How can I convert a Docker image into a (vagrant) VirtualBox box?

Question

I've been looking at Packer.io, and would love to use it to provision/prepare the vagrant (VirtualBox) boxes used by our developers.

I know I could build the boxes with VirtualBox using the VirtualBox Packer builder, but find the layer stacking of Docker to provide a much faster development process of the boxes.

How do I produce the image with a Dockerfile and then export it as a Vagrant box?

Answer 1

Find the size of the docker image from docker images

REPOSITORY   TAG    IMAGE ID       CREATED             SIZE
mybuntu   1.01   7c142857o35   2 weeks ago         1.94 GB

Run a container based on the image docker run mybuntu:1.01

Create a QEMU image from the container, Also, use the size of the image in the first command (seek=IMAGE_SIZE). And, for the docker export command retrieve the appropriate container id from docker ps -a

dd if=/dev/zero of=mybuntu.img bs=1 count=0 seek=2G
mkfs.ext2 -F mybuntu.img
sudo mount -o loop mybuntu.img /mnt
docker export <CONTAINER-ID> | sudo tar x -C /mnt
sudo umount /mnt

Use qemu-utils to convert to vmdk

sudo apt-get install qemu-utils
qemu-img convert -f raw -O vmdk mybuntu.img mybuntu.vmdk

More info on formats that are available for conversion can be found here. Now you can import the vmdk file in virtualbox