Ideally, yes you would want a single Docker image. That's somewhat the point of Docker, to isolate your app and have it run the same, everywhere. If you use mul

Ideally, yes you would want a single Docker image. That's somewhat the point of Docker, to isolate your app and have it run the same, everywhere. If you use multiple images, then you're circumventing that benefit. You could install all the dev gems, build tools, etc in the CircleCI build container and run unit testing. Once everything looks good and you can build your file app that passes, then take the app and throw it in a new Docker image. Then, integration test that Docker image itself. That final piece could be done on some sort of staging server of in a new build environment using CircleCI 2.0 Workflows.