Switching to FAI (Fully Automatic Installer) for creating Vagrant Boxes

Have you heard of Vagrant ? It is a command line tool to get ready to use, disposable Virtual Machines (VM) from an online catalog. Vagrant works on Linux, FreeBSD, Windows and Mac and you only need three commands to get a shell prompt in a VM (see the Debian wiki).
The online catalog has images for the majority of the OSes you can think of.

We've been building the Debian disk images for Vagrant (available on https://app.vagrantup.com/debian/) with a number of tools over the years:

• first the ad-hoc https://github.com/EmmanuelKasper/vagrant-debian-wheezy-64 which was hacking the Debian installer CD with a builtin preseed file, and passed that CD to a VirtualBox VM to automate the installer

• then vmdebootstrap, which is one of the many different wrappers over debootstrap, which creates a debian install on a loopback mounted filesystem.
  

• then packer, which is wrapping qemu and the Debian installer CD with automated bootparams and preseed file.
  

• and then fai-diskimage, again a wrapper over debootstrap using loopback mounts

Basically there are two category of tools for building a disk image:

- those using an emulator and the OS installer in a automated way

- those using debootstrap/pacstrap/rpmstrap on a loopback mounted filesystem

Personally I prefer the first approach, as you can run the build process as non root, and you benefit from all the quality work of the official installer.
However this requires virtualization, and nested virtualization if your build process run insides a VM. Unfortunately nested virtualization is not that common, for instance my cloud provider, and the VMs used for Debian Continuous Integration, are not supporting nested virtualization.
As the maintainer of fai-diskimage is a Debian Developer (hey MrFAI ! :) and as the debian-cloud folks are it using for Amazon, Azure and Google Cloud Debian images, it made sense to switch to fai-diskimage for now. The fai-diskimage learning curve is a bit steep as you have to learn many internal concepts before using it, but once you get the bits connected it works quite well.