There are actually two ways to do Docker with Heroku. You can let Heroku build your image during the deployment phase by simply having a `Dockerfile` in your r

There are actually two ways to do Docker with Heroku. You can let Heroku build your image during the deployment phase by simply having a `Dockerfile` in your repository [1]. Or, you can build the image yourself on your CI service and push it to Heroku's registry and then trigger a release. This last option is useful if you want to run tests against the exact image that is going to be deployed without having to rebuilt it [2]. [1] https://blog.heroku.com/build-docker-images-heroku-yml https://blog.heroku.com/build-docker-images-heroku-yml [2] https://devcenter.heroku.com/articles/container-registry-and-runtime#building-and-pushing-image-s https://devcenter.heroku.com/articles/container-registry-and...