How to keep DRY with a ActiveAdmin or RailsAdmin, separate from the main application

Question

I am building a JSON-only application, it is basically a leaner Rails, with fewer middleware and fewer modules. This is an application being built in Rails 4.

I want to

Answer 1

This blog post describes an interesting approach: https://content.pivotal.io/blog/migrating-from-a-single-rails-app-to-a-suite-of-rails-engines

They use a nearly empty app as a container and mount their actual apps as Rails Engines.