Things you need to Learn

Please visit my blog post to learn about Docker and its installation from Containarization and Docker.

Using docker-compose to dockerize the app

Steps:-

1. Chdir to the project directory

2. Create an entry point file called docker-entrypoint.sh

    #!/bin/bash
   
    set -e
   
    bundle check || bundle install --binstubs="$BUNDLE_BIN"
   
    echo "command executing $@"
    exec "$@"
   

3. Create a Dockerfile with the content like below:

    FROM ruby:2.6.3
    # Needed to compile nodejs
    RUN apt-get update -qq && apt-get install -y build-essential
    RUN apt-get install -y libpq-dev
    RUN apt-get install -y libxml2-dev libxslt1-dev
    RUN apt-get install -y nodejs
   
    RUN mkdir /app
    WORKDIR /app
    ADD . /app
   
    EXPOSE 3000
   
    COPY ./docker-entrypoint.sh /
    RUN chmod +x /docker-entrypoint.sh
    ENTRYPOINT ["/docker-entrypoint.sh"]
   
    ENV BUNDLE_PATH=/bundle \
        BUNDLE_BIN=/bundle/bin \
        GEM_HOME=/bundle
    ENV PATH="${BUNDLE_BIN}:${PATH}"
    RUN gem install bundler
   

4. Create docker-compose-yml file

    version: '3'
   
    services:
      postgres:
        image: postgres:9.6
        ports:
          - '5432:5432'
        volumes:
          - postgres:/var/lib/postgresql/data
   
      web:
        build: .
        command: puma # we are using puma
        volumes:
          - bundle:/bundle
          - .:/app
        ports:
          - '3000:3000'
        links:
          - postgres
   
    volumes:
      bundle:
      postgres:
   

5. database.yml file need to change

   
    development:
      <<: *default
      host: postgres # service name in docker-compose.yml
      username: postgres # has to be this way
      password:
      database: my_app_development
   

   postgres is the name of the service which will be your host.

1. Everytime you change Dockerfile, you need to rebuild the image using docker-compose build

2. You need to create the database the first time

    docker-compose run web rails db:create && rails db:migrate && rails db:seed
   

   or you can run

    docker-compose run web rails db:create
    docker-compose run web rails db:migrate
    docker-compose run web rails db:seed

Then, your application will be available via localhost:3000 in browsers.

Summary

In this way you can move your existing Rails 5/6 projects to Docker using Docker Compose.

References

bundler.io/v2.0/guides/bundler_docker_guide..