How to install Docker in the local environment of an existing Rails application [Rails 6 / MySQL 8]

Introduction

This article is the procedure when I introduced Docker to the local environment of the existing portfolio app. Since the official document of Docker is the procedure explanation in PostgreSQL, there is no procedure explanation of the official document when it comes to MySQL. Also, the information on Rails6 is still less than that on Rails5, and as a result, the information on the combination of Rails6 + MySQL was very little. As a result, I got various errors and tried and errored myself, so I hope this article will help those who introduce Docker with the combination of Rails6 + MySQL. Since the author is a beginner who has no practical experience in job hunting, there may be some mistakes. In that case, I would appreciate it if you could let me know in the comments.

Prerequisites

• The installation of Docker Desktop for Mac` has been completed.
• Docker is already started

• In the case of the author, the above installation and startup was done while watching "Building an application execution environment with Docker starting from scratch". It is very easy to understand and recommended for learning the whole picture of Docker.

version

• Ruby 2.6.5
• Rails 6.0.3.2
• MySQL 8.0.21

Step 1 Create Dockerfile

Create a Dockerfile in the root directory of the existing application and write as follows. ** * This time, the directory name of the application is sample_app. Replace this with the directory name of your app. ** **

Dockerfile

FROM ruby:2.6.5
RUN curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add - \
    && echo "deb https://dl.yarnpkg.com/debian/ stable main" | tee /etc/apt/sources.list.d/yarn.list
RUN apt-get update -qq && apt-get install -y build-essential libpq-dev nodejs yarn
WORKDIR /sample_app
COPY Gemfile ./Gemfile
COPY Gemfile.lock ./Gemfile.lock
RUN gem install bundler
RUN bundle install
COPY . /sample_app
COPY entrypoint.sh /usr/bin/
RUN chmod +x /usr/bin/entrypoint.sh
ENTRYPOINT ["entrypoint.sh"]
EXPOSE 3000
CMD ["rails", "server", "-b", "0.0.0.0"]

Step 2 Create docker-compose.yml

As in step 1, create docker-compose.yml in the root directory of the existing application and write it as follows.

docker-compose.yml

version: '3' #docker-compose version
services:
  db:
    image: mysql:8.0.21 #Combine with existing apps. To the terminal[$ mysql --version]Confirm with
    environment:
      MYSQL_ROOT_PASSWORD: vxgbizakqc #Your password
      MYSQL_DATABASE: root
    ports:
      - "4306:3306"
    volumes:
      - ./mysql-confd:/etc/mysql/conf.d
  web:
    build: .
    command: bash -c "rm -f tmp/pids/server.pid && bundle exec rails s -p 3000 -b '0.0.0.0'"
    volumes:
      - .:/sample_app
    ports:
      - 3000:3000
    depends_on:
      - db
    tty: true
    stdin_open: true
volumes:
  mysql-data:

Step 3 Create entrypoint.sh

As with steps 1 and 2, create entrypoint.sh in the root directory of the existing application and write it as follows.

entrypoint.sh

#!/bin/bash
set -e

# Remove a potentially pre-existing server.pid for Rails.
rm -f /sample_app/tmp/pids/server.pid

# Then exec the container's main process (what's set as CMD in the Dockerfile).
exec "$@"

Step 4 Edit config / database.yml

Edit database.yml in the config directory as follows.

config/database.yml

default: &default
  adapter: mysql2
  encoding: utf8mb4
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
  username: root
  password: vxgbizakqc #Your password
  socket: /tmp/mysql.sock
  host: db

development:
  <<: *default
  database: sample_app_development

test:
  <<: *default
  database: sample_app_test

Step 5 Create a Docker image

Execute the following command in the terminal to create a Docker image.

Terminal

MacBook-Pro:sample_app$ docker-compose build

Step 6 Start the Docker container

Execute the following command in the terminal to start the Docker container.

Terminal

MacBook-Pro:sample_app$ docker-compose up -d

Step 7 Create a database in the container

Execute the following command in the terminal to create the database in the container.

Terminal

MacBook-Pro:sample_app$ docker-compose run web rails db:create

When you execute the above command, a database will be created based on the database.yml edited earlier. If the database is created successfully, the following will be displayed.

Terminal

reating sample_app_web_run ... done
Created database 'sample_app_development'
Created database 'sample_app_test'

Step 8 Execute migration of the created database

Execute the following command in the terminal to execute the database migration.

Terminal

MacBook-Pro:sample_app$ docker-compose run web rails db:migrate

If the database migration is successful, the following will be displayed.

Terminal

Creating sample_app_web_run ... done
== 20209165960112 DeviseCreateUsers: migrating ================================
-- create_table(:users)
   -> 0.0253s

　　#Omission

-- add_index(:notifications, :comment_id)
   -> 0.0251s
== 20209165960112 CreateNotifications: migrated (0.1280s) =====================

Step 9 Install Gem

Well, this is the last of the long introduction of Docker. Execute the following command in the terminal to install Gem.

Terminal

MacBook-Pro:sample_app$ docker-compose exec web bundle install

that's all! !! You can see the application by connecting to localhost: 3000.

References

This time, I was able to introduce Docker as a result of referring to the following articles and video teaching materials. Thank you to the people who wrote the article and Mr. Kojima, the creator of the video teaching materials.

• Create an environment that can execute system specifications with CircleCI while converting an existing Rails 6 application to Docker
• Steps for building a Ruby on Rails environment with Docker [Rails 6 compatible]
• Procedure to install Docker in existing Rails app
• [Docker environment construction / Rails6 ~, MySQL] Procedure for migrating an existing application being created in the local environment to the Docker environment
• "Building an application execution environment with Docker starting from scratch"