FreeBSD security officer Colin Percival has posted a blog regarding an AMI builder on FreeBSD via his website Daemonic Dispatches.

I’ve been working on the FreeBSD/EC2 platform for a long time; five years ago I finally had it running, and for the past few years it has provided the behaviour FreeBSD users expect — stability and high performance — across all EC2 instance types. Making the platform work was just the first step though; next comes making it usable.

Some people are happy with simply having a virtual machine which runs the base FreeBSD system; for them, the published FreeBSD/EC2 images (which, as of FreeBSD 10.2-RELEASE, are built by the FreeBSD Release Engineer) will be sufficient. For users who want to use “stock” FreeBSD but would like to have some extra setup performed when the instance launches — say, to install some packages, edit some configuration files, and enable some services — I wrote the configinit tool. And for users who need to make changes to FreeBSD itself, I added code for building AMIs into the FreeBSD source tree, so you can take a modified FreeBSD tree and run make ec2ami to generate a reusable image.

Full blog post: http://www.daemonology.net/blog/2015-11-21-FreeBSD-AMI-builder-AMI.html