Why is docker not forwarding to a local rails

[Warning] One or more build-args [BUNDLE_GITHUB__COM] were not consumed
Successfully built 2f3e0625b750
Successfully tagged hokusai_doppler:latest
Recreating hokusai_doppler_1 ... done
Attaching to hokusai_doppler_1
doppler_1  | 20:01:33 web.1  | started with pid 7
doppler_1  | 20:01:36 web.1  | => Booting Unicorn
doppler_1  | 20:01:36 web.1  | => Rails 4.2.11 application starting in development on http://localhost:8080
doppler_1  | 20:01:36 web.1  | => Run `rails server -h` for more startup options
doppler_1  | 20:01:36 web.1  | => Ctrl-C to shutdown server
doppler_1  | 20:01:37 web.1  | I, [2019-01-28T20:01:37.292867 #7]  INFO -- : listening on addr=127.0.0.1:8080 fd=11
doppler_1  | 20:01:37 web.1  | I, [2019-01-28T20:01:37.293060 #7]  INFO -- : worker=0 spawning...
doppler_1  | 20:01:37 web.1  | I, [2019-01-28T20:01:37.298972 #7]  INFO -- : master process ready
doppler_1  | 20:01:37 web.1  | I, [2019-01-28T20:01:37.300235 #12]  INFO -- : worker=0 spawned pid=12
doppler_1  | 20:01:37 web.1  | I, [2019-01-28T20:01:37.301602 #12]  INFO -- : worker=0 ready
^CGracefully stopping... (press Ctrl+C again to force)
Stopping hokusai_doppler_1   ... 
Stopping hokusai_doppler_1   ... done
Stopping hokusai_doppler_1 ... done
~/source/artsy/doppler/dblock (master)$ hokusai dev start
Starting development environment... Press Ctrl+C to stop.
WARNING: The BUNDLE_GITHUB__COM variable is not set. Defaulting to a blank string.
Building doppler
Step 1/11 : FROM ruby:2.4.5-alpine
 ---> 45418ec53685
Step 2/11 : ENV PORT 8080
 ---> Using cache
 ---> 371eab5a6ea5
Step 3/11 : EXPOSE 8080
 ---> Using cache
 ---> 27fecd6bf5e4
Step 4/11 : WORKDIR /app
 ---> Using cache
 ---> 9c158b5a67ad
Step 5/11 : RUN apk --no-cache add       build-base       nodejs       tzdata       linux-headers       bash
 ---> Using cache
 ---> 14bdec8357c5
Step 6/11 : COPY .ruby-version Gemfile* ./
 ---> Using cache
 ---> 306496e02fbc
Step 7/11 : RUN gem install bundler &&     bundle install --frozen
 ---> Using cache
 ---> b2cbff960cc7
Step 8/11 : COPY . ./
 ---> 03d7c0932eaf
Step 9/11 : RUN adduser -D deploy &&     chown -R deploy:deploy /app
 ---> Running in 3378b1382cc8
Removing intermediate container 3378b1382cc8
 ---> b74ba81aeea7
Step 10/11 : USER deploy
 ---> Running in 9ced63a60371
Removing intermediate container 9ced63a60371
 ---> fc87b06d5808
Step 11/11 : CMD foreman start
 ---> Running in 50114e855c01
Removing intermediate container 50114e855c01
 ---> aae205257ca5
[Warning] One or more build-args [BUNDLE_GITHUB__COM] were not consumed
Successfully built aae205257ca5
Successfully tagged hokusai_doppler:latest
Recreating hokusai_doppler_1 ... done
Attaching to hokusai_doppler_1
doppler_1  | 20:01:50 web.1  | started with pid 7
doppler_1  | 20:01:51 web.1  | I, [2019-01-28T20:01:51.416611 #7]  INFO -- : listening on addr=0.0.0.0:8080 fd=9
doppler_1  | 20:01:51 web.1  | I, [2019-01-28T20:01:51.416737 #7]  INFO -- : worker=0 spawning...
doppler_1  | 20:01:51 web.1  | I, [2019-01-28T20:01:51.419424 #7]  INFO -- : master process ready
doppler_1  | 20:01:51 web.1  | I, [2019-01-28T20:01:51.420472 #10]  INFO -- : worker=0 spawned pid=10
doppler_1  | 20:01:51 web.1  | I, [2019-01-28T20:01:51.421182 #10]  INFO -- : Refreshing Gem list
doppler_1  | 20:01:55 web.1  | I, [2019-01-28T20:01:55.144100 #10]  INFO -- : worker=0 ready

Start by comparing the two startup logs, especially Rails binding to 127.0.0.1:8080 versus 0.0.0.0:8080, and inspect the Docker and Rails development startup configuration mentioned by the report. Done means the local Rails application is reachable through the intended forwarded port from outside the container.