[RUBY] [Rails] How to build an environment with Docker

Development environment

・ Docker: 19.03.8 -Docker-Compose: 1.25.5 ・ Ruby: 2.5.7 Rails: 5.2.4 ・ Vagrant: 2.2.7 -VirtualBox: 6.1 ・ OS: macOS Catalina


1. Create / move working directory

The folder name will be myapp (anything is fine).


$ mkdir myapp


$ cd myapp

2. Create / edit Dockerfile


$ vi Dockerfile


FROM ruby:2.7.1
RUN apt-get update -qq && apt-get install -y nodejs postgresql-client
RUN mkdir /myapp
WORKDIR /myapp
COPY Gemfile /myapp/Gemfile
COPY Gemfile.lock /myapp/Gemfile.lock
RUN bundle install
COPY . /myapp

#Added a script that runs every time the container starts
COPY entrypoint.sh /usr/bin/
RUN chmod +x /usr/bin/entrypoint.sh
ENTRYPOINT ["entrypoint.sh"]

#Start main process
CMD ["rails", "server", "-b", ""]


★ Overview

FROM: Set the image and version to use RUN: Command execution WORKDIR: Set the working directory COPY: Copy local files to container ʻENTRYPOINT: Set the command to be executed first ʻEXPOSE: Set the port number on which the container listens CMD: Software execution inside the image

★ Details

** ◎ Obtain the latest stable version as of July 19, 2020 as an image to use. ** **

FROM ruby:2.7.1

** ◎ Install Node.js and PostgreSQL packages. ** **

RUN apt-get update -qq && apt-get install -y nodejs postgresql-client

** ◎ Create a myapp directory inside the container. ** **

RUN mkdir /myapp

** ◎ Set the working directory to the myapp created above **

WORKDIR /myapp

** ◎ Copy the local Gemfile to myapp in the container. ** **

COPY Gemfile /myapp/Gemfile

** ◎ Copy the local Gemfile.lock to myapp in the container. ** **

COPY Gemfile.lock /myapp/Gemfile.lock

** ◎ Execute bundle install. ** **

RUN bundle install

** ◎ Copy the current directory (local myapp) to myapp in the container. ** **

COPY . /myapp

** ◎ Copy the local ʻentrypoint.sh to ʻusr / bin in the container. ** **

COPY entrypoint.sh /usr/bin/

** ◎ Allow access to ʻentrypoint.sh` copied above. ** **

RUN chmod +x /usr/bin/entrypoint.sh

** ◎ Set ʻentrypoint.sh` as the first command to be executed when the container is started. ** **

ENTRYPOINT ["entrypoint.sh"]

** ◎ Set the port number to 3000. ** **


** ◎ Launch the Rails server. ** **

CMD ["rails", "server", "-b", ""]

3. Create / edit Gemfile

Specify the Rails version. This time we will make it compatible with Rails 6.


$ vim Gemfile


source 'https://rubygems.org'
gem 'rails', '~> 6'

4. Create Gemfile.lock


$ touch Gemfile.lock

5. Create / edit ʻentrypoint.sh`


$ vi entrypoint.sh


set -e

#Rails compatible file server.Delete the pid as it may exist.
rm -f /myapp/tmp/pids/server.pid

#Run the container process. (The one set in CMD in the Dockerfile.)
exec "$@"

5. Create / edit docker-compose.yml


$ vi docker-compose.yml


version: '3'
    image: postgres
      - ./tmp/db:/var/lib/postgresql/data
      POSTGRES_PASSWORD: password
    build: .
    command: bash -c "rm -f tmp/pids/server.pid && bundle exec rails s -p 3000 -b ''"
      - .:/myapp
      - "3000:3000"
      - db


version: Set the version of docker-compose. services: Create services in the hash below. You can name it freely, but usually you name it web and db. ʻImage: image to use (specify PostgreSQL in db) volumes: Directory mount settings (db data etc. can be left) build: Path with Dockerfile etc. (basically current directory) command: Command (delete the server.pid file and then start the rails server) ports: Port number (host: set in container) depends_on`: Shows the dependencies and allows you to specify the startup order. Here, start from db → web.

6. Check the directory structure


- Dockerfile
- Gemfile
- Gemfile.lock
- entrypoint.sh
- docker-compose.yml

7. Build the project


$ docker-compose run web rails new . --force --no-deps --database=postgresql --skip-bundle


--force: Overwrite Gemfile --no-deps: Do not start the linked service --database = postgresql: Specify PostgreSQL for DB --skip-bundle: Skip bundle

8. Run bundle install


Could not find gem 'pg (>= 0.18, < 2.0)' in any of the gem sources listed in your Gemfile.
Run `bundle install` to install missing gems.

I think that the above error occurred in 7, so execute the following command to solve it. It will bundle install when you build the Docker image.


$ docker-compose build

9. Edit database.yml


#Change before
default: &default
  adapter: postgresql
  encoding: unicode
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>

#After change
default: &default
  adapter: postgresql
  encoding: unicode
  host: db
  username: postgres
  password: password
  pool: 5

10. Start the container


$ docker-compose up

* If the following error occurs


Error: No such file or directory @ rb_sysopen - /myapp/config/webpacker.yml (RuntimeError)

Create / edit webpacker.yml


touch config/webpacker.yml


# Note: You must restart bin/webpack-dev-server for changes to take effect

default: &default
  source_path: app/javascript
  source_entry_path: packs
  public_root_path: public
  public_output_path: packs
  cache_path: tmp/cache/webpacker
  webpack_compile_output: true

  # Additional paths webpack should lookup modules
  # ['app/assets', 'engine/foo/app/assets']
  additional_paths: []

  # Reload manifest.json on all requests so we reload latest compiled packs
  cache_manifest: false

  # Extract and emit a css file
  extract_css: true

    - .jpg
    - .jpeg
    - .png
    - .gif
    - .tiff
    - .ico
    - .svg
    - .eot
    - .otf
    - .ttf
    - .woff
    - .woff2

    - .mjs
    - .js
    - .sass
    - .scss
    - .css
    - .module.sass
    - .module.scss
    - .module.css
    - .png
    - .svg
    - .gif
    - .jpeg
    - .jpg

  <<: *default
  compile: true

  # Set to false if using HMR for CSS
  extract_css: true

  # Reference: https://webpack.js.org/configuration/dev-server/
    https: false
    host: localhost
    port: 3035
    public: localhost:3035
    hmr: false
    # Inline should be set to true if using HMR
    inline: true
    overlay: true
    compress: true
    disable_host_check: true
    use_local_ip: false
    quiet: false
    pretty: false
      'Access-Control-Allow-Origin': '*'
      ignored: '**/node_modules/**'

  <<: *default
  compile: true

  # Compile test packs to a separate directory
  public_output_path: packs-test

  <<: *default

  # Production depends on precompilation of packs prior to booting for performance.
  compile: false

  # Cache manifest.json for performance
  cache_manifest: true

11. Create database


docker-compose run web rake db:create

* If the following error occurs


could not translate host name "db" to address: Name or service not known


Error: Database is uninitialized and superuser password is not specified.

Edit docker-compose.yml


#Change before

#After change

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