Firstly, install Docker.
Then execute the following commands:
$ git clone git@github.com:lukehorvat/rails-issue-21193.git
$ cd rails-issue-21193
$ docker build -t rails-issue-21193 .
$ docker run -p 9000:9000 -d rails-issue-21193If everything is set up properly, you should see a welcome message from nginx when you navigate to http://<host-ip>:9000/ in a web browser.
Next, navigate to http://<host-ip>:9000/app/, which is the subdirectory where the Rails app is hosted. Immediately, you'll notice that it redirects to http://<host-ip>:9000/ui/. But based on the configuration in routes.rb, it really should redirect to http://<host-ip>:9000/app/ui/ instead.
Bug?