Rails, Ember, Redis, nginx and docker

Colleagues, I have a front-end application based on Ember and Rails (running on nginx) which also uses redis as a cache.

I want to dockerize this application, but not sure about best practices. Would it be best to create one container with a dockerfile that pulls in all these pieces, or should each component be in its own container?

For bonus points: I have to retrieve the code from private bitbucket repos and.. how are we meant to store our secrets and other config files when using containers?