My phoenix-based project uses two Dockerfiles. There is one for local
development and CI and another one for production. Ideally I would want one
Dockerfile; use the same image for local and production. But ease of
development is also important.
Phoenix supports live-reload during development. The feature is very convenient; change a file, see the change without restarting the server.
I need to give docker access to my filesystem so that I can use live-reload. When I start my application in a container, I mount my code as a volume that the docker container can access. Then, live-reload will be able to catch the code changes I make without needing to restart the server or the container.
My app deploys to Heroku. Heroku does not support volume mounting. My CI process
uses a second Dockerfile that copies the codebase to the docker image. Now I
have two Dockerfiles: local and production. I will trade-off this bit of
duplication for the sake of development productivity.