This example template uses a (proposed) new flag for Packer's amazon-chroot builder to construct an Arch AMI on a new disk volume using a running AWS instance to execute the build. It does not depend on any pre-existing disk image and its only external dependency is the Arch package repos. This image will boot a functioning instance with ssh running.
This requires either an existing Arch instance or another Linux instance to execute the build process. See:
https://wiki.archlinux.org/index.php/Install_from_existing_Linux
The arch-install-scripts and parted packages are required.
This does not currently implement disk resizing and most of the cloud-init features are untested.