How to access Sinatra port using Docker with docker-compose run

Question

I'm not sure how to a correctly expose the Sinatra port 4567 from Docker back to the host. Running the app locally has no issues.

The following repository show cases the issue https://gitlab.com/davidhooey/sinatra-docker

From searching I noticed the following issue Running Ruby Sinatra inside a Docker container not able to connect (via Mac host) or find commands (in different scenario)? where the --host 0.0.0.0 is passed into the rackup command. However, I'm launching the site programmatically through using Site.run!.

File tree

.
├── Dockerfile
├── Gemfile
├── Gemfile.lock
├── README.md
├── app.rb
├── docker-compose.yml
├── site.rb
└── views
    └── index.erb

app.rb

module App
    class App
        def initialize(args)
            # Do some stuff before launching site.
            # Launch site
            Site.run!
        end
    end
end

App::App.new(ARGV)

In site.rb the :bind Sinatra setting is set to 0.0.0.0.

site.rb

require 'sinatra'

module App
    class Site < Sinatra::Base
        set :bind, '0.0.0.0'
        set :static, true
        set :public_dir, File.expand_path(__dir__)

        get '/' do
            erb :'/index'
        end
    end
end

Even still the site is inaccessible when run within a Docker container.

Dockfile

FROM ruby:2.2.6

EXPOSE 4567

RUN mkdir /app
WORKDIR /app
COPY . /app

RUN gem install bundler && bundle install

CMD ["/bin/bash"]

docker-compose.yml

version: '3.2'

services:
    app:
        build: .
        hostname: app
        ports:
            - "4567:4567"
        environment:
            - RUBYOPT=-W0 -KU -E utf-8:utf-8
        volumes:
            - type: bind
              source: .
              target: /app

Local works:

ruby app.rb

Docker not so much:

docker-compose build
docker-compose run --rm app ruby app.rb

Docker run example.

$ docker-compose run --rm app ruby app.rb
[2018-07-27 14:21:10] INFO  WEBrick 1.3.1
[2018-07-27 14:21:10] INFO  ruby 2.2.6 (2016-11-15) [x86_64-linux]
== Sinatra (v2.0.3) has taken the stage on 4567 for development with backup from WEBrick
[2018-07-27 14:21:10] INFO  WEBrick::HTTPServer#start: pid=1 port=4567

Launch a bash shell into the running container to access Sinatra within the container.

$ docker exec -it aa8f64b009b0 bash
root@app:/app# curl localhost:4567
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>Sinatra Docker</title>
    </head>
   <body>
        <h1>Sinatra Docker</h1>
   </body>
</html>
root@app:/app#

Any ideas are more than welcome on how to access the Sinatra port running within the container from the localhost when Sinatra is launched programmatically.

Did you log into the docker image to check that your app is running properly and bound to an interface? — Casper
I have added the Docker Run, showing the startup of Sinatra within the container. Seems like it is starting on the port without issues. — hooinator

Casper Casper · Accepted Answer · 2018-07-27T17:34:01

When running an app with docker-compose run, service ports will not be mapped. This is by design, because run is meant for one-off tasks and not for booting the whole compose stack.

See documentation here:
https://docs.docker.com/compose/reference/run/

The second difference is that the docker-compose run command does not create any of the ports specified in the service configuration. This prevents port collisions with already-open ports.

To map the ports you either need to use run with --service-ports, or add a command section to your docker-compose.yml and then use docker-compose up:

Option 1 (using run):

docker-compose run --service-ports --rm app ruby app.rb -o 0.0.0.0

Option 2 (booting the whole stack):

services:
  app:
    build: .
    hostname: app
    command: ruby app.rb -o 0.0.0.0  # <-- Add this
    ports:
      - "4567:4567"
    ...

And then:

docker-compose up

How to access Sinatra port using Docker with docker-compose run

1 Answers