Did you know that you can change the error messages displayed by the browser when using HTML5 form validation features?
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.