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Question

I'm learning docker and create a Dockerfile which is exactly

FROM ruby:2.6
RUN bundle config --global frozen 1

WORKDIR /usr/src/app

COPY Gemfile Gemfile.lock ./

RUN bundle install

COPY . .

EXPOSE 3000

CMD ["rails", "server", "-b", "0.0.0.0", "-p", "3000"]

but when I try curl 0.0.0.0:3000 or open it in a browser it says connection is refused. It should not related with the rails app I think because it's just a completely new app.

after I input Ctrl-c then it show

=> Booting Puma
=> Rails 5.2.3 application starting in development 
=> Run `rails server -h` for more startup options
Puma starting in single mode...
* Version 3.12.1 (ruby 2.6.3-p62), codename: Llamas in Pajamas
* Min threads: 5, max threads: 5
* Environment: development
* Listening on tcp://0.0.0.0:3000
Use Ctrl-C to stop
- Gracefully stopping, waiting for requests to finish
=== puma shutdown: 2019-05-05 04:00:42 +0000 ===
- Goodbye!
Exiting

I tried to attach shell into container and I saw puma with ps aux so what is wrong

Answer 1

It's important how you start your container. By default you don't publish the port to the host machine so the opened port of your rails application is only accessible inside of your container. If you want to publish the port run it like that:

docker run -p 3000:3000 <image>

You can find more information in the documentation .