ERR_CONNECTION_REFUSED by docker container - ruby-on-rails

Question

I'm new to Docker and trying to make a demo Rails app. I made a dockerfile that looks like this:
FROM ruby:2.2
# Install apt based dependencies required to run Rails as
# well as RubyGems. As the Ruby image itself is based on a
# Debian image, we use apt-get to install those.
RUN apt-get update && apt-get install -y \
build-essential \
nodejs
# Configure the main working directory. This is the base
# directory used in any further RUN, COPY, and ENTRYPOINT
# commands.
RUN mkdir -p /app
WORKDIR /app
# Copy the Gemfile as well as the Gemfile.lock and install
# the RubyGems. This is a separate step so the dependencies
# will be cached unless changes to one of those two files
# are made.
COPY Gemfile Gemfile.lock ./
RUN gem install bundler && bundle install --jobs 20 --retry 5
# Copy the main application.
COPY . ./
# Expose port 3000 to the Docker host, so we can access it
# from the outside.
EXPOSE 3000
# The main command to run when the container starts. Also
# tell the Rails dev server to bind to all interfaces by
# default.
CMD ["bundle", "exec", "rails", "server", "-b", "0.0.0.0"]
I then built it (no errors):
docker build -t demo .
And then run it (also no errors):
docker run -itP demo
=> Booting Puma
=> Rails 5.1.1 application starting in development on http://0.0.0.0:3000
=> Run `rails server -h` for more startup options
Puma starting in single mode...
* Version 3.8.2 (ruby 2.2.7-p470), codename: Sassy Salamander
* Min threads: 5, max threads: 5
* Environment: development
* Listening on tcp://0.0.0.0:9292
Use Ctrl-C to stop
When I run a docker ps command in a separate terminal to determine the ports, I get:
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
55e8224f7c15 demo "bundle exec rails..." About an hour ago Up About an hour 0.0.0.0:32772->3000/tcp ecstatic_bohr
However, when I try to connect to it at either http://localhost:32772 or http://192.168.99.100:32772 using Chrome or via a curl command, I receive a "Connection refused".
When I run the app outside of docker on my local machine via bundle exec rails server command, it works fine. Note that I am using Docker Toolbox on my Win7 machine
What could I be doing wrong ?

Answer 1

I spend a couple of hours on this as well and this thread was really helpful. What i'm doing right now is accessing those services through the vm's ip address.
You can get your vm's address running:
docker-machine ls
then try to access your service using the host mapped port 37772, something like this:
http://<VM IP ADDRESS>:32772
Hope this helps.

Answer 2

The combination of the above tricks worked--
I had to use http://<VM IP ADDRESS>:32772 (localhost:32772 did NOT work), AND I had to fix my exposed port to match the TCP listening port of 9292.
I still don't understand why the TCP listening port defaulted to 9292 instead of 3000, but I'll look into that separately.
Thank you for the help!