ansible can be used to build container images in an idempotent way. And ansible is greatat creating deployment logic among other things. Where puppet , chef et al. are primarily for automating a direct machine, Ansible is a general purpose automation framework. Terraform is definitely better at provisioning cloud resources, but Ansible is much better at automating pretty much anything else that you could think of.

I use Ansible to harden my servers, configure ssh, deploy private keys, install Docker, and start all my Docker services.