Thanks for pointing me to Racker (https://github.com/aspring/racker). I'm currently building Packer and Terraform images with chunked together Python scripts that work, but I wouldn't call them a great solution. I'm actually using Packer specifically so I can start with regular EC2, and then move to a more Docker-based infrastructure.
Packer severely frustrates me, with the maddening regularity in which it fails just for funsies. Or the consistent but completely inane ways that it fails, like refusing to proceed based on not finding a builder for an 'only' or 'except' clause (making it nearly impossible to re-use provisioners and post-provisioners across multiple projects). Racker does help--my shared Racker scripts are in a Ruby gem--though I think that it pretty much removes Packer as anything more than a dummy solution into which you dump directives on a per-builder basis. As a tool that you carefully feed the bare minimum of information to do its job in any specific situation, though, it works okay.
Terraform, on the other hand, I think is a huge, huge mess, and I don't think they're going to fix it. I wrote a Ruby DSL for it the last time I tried to use it in anger, only to encounter that Terraform didn't honor its own promises around the config language it insisted on instead of YAML or a full-featured DSL of its own. Current client uses it, and every point release adds new and exciting bugs and regressions in stuff that should be caught by the most trivial of QA. For AWS, I strongly recommend my friend Sean's Cfer[1] as a better solution; CloudFormation's kind of gross, but Cfer helps.
