I'm very interested in the "seamless DevOps" part. Could you point me to some link describing how you manage to achieve that with phoenix ? (do you use docker + kubernetes, or OTP, or something else ?)
Have a look at distillery for building Elixir releases, and edeliver for deployment.
As others have suggested, use Distillery + Edeliver for zero-downtime deployment.
Step-by-step instructions here: https://git.io/fjcVz (happy to answer any questions you have, please open issues on GitHub as we have no way of checking notifications on HN)