Custom system images
Use a VMDK image file (example with VirtualBox and Ubuntu)
Bash script to install CoreOS:
https://github.com/azediv/gnadi-coreos
Gandis' gandi-vm-config:
https://github.com/Gandi/gandi-vm-config
Gandi's swap-setup:
https://github.com/Gandi/gandi-swapsetup
How we created the FreeBSD image:
https://wiki.gandi.net/en/iaas/references/freebsd
How a virtual machine is setup:
http://gandikitchen.net/post/2013/11/15/How-is-a-virtual-machine-set-up