I love software that "just works", and packer.io is one of them. It builds disk images in various image formats and for various cloud providers.
With a small JSON configuration file, a kickstart file, and a set of provisioning scripts, I can have a QEMU image automatically built from the install CD and customised as I wish.
With a different config file, I can have the same thing for EC2 images.
And because it's JSON, I can dynamically generate custom configuration files quickly and easily.
There seems to be a positive trend of self-contained, single-purpose and well designed software coming from the Golang camp. Keep at it! :-)