If your Phoenix app uses basic authentication or cookies for authentication, you need to protect it from cross-site request forgery.
If you think the only purpose of a code review is to catch bugs, read this.
If you ever configured CircleCI to do a deployment, you probably ran into the problem of two pushes triggering two deployments at the same time. You can prevent that.
Here's how I went from knowing exactly zero about AWS to getting the Solutions Architect - Associate certification.
With either HTTPotion or HTTPoison.