はじめに

Rails+PostgreSQLの環境を、docker-composeで構築する手順を紹介します。

Version

Ruby 2.5.0
Rails 5.1.4
Postgresql 10.1

ファイル構成

以下のような構成で作成します。

./
|- app/  //共有フォルダ
|- docker-compose.yml
|- web/
   |- Dockerfile

Dockerfileの作成

RailsとPostgreSQLのライブラリを導入します。
ここでホストフォルダと共有するappフォルダも作成しておきます。

Dockerfile

FROM ruby:2.5.0

RUN apt-get update && apt-get install -y build-essential libpq-dev postgresql-client
RUN gem install rails
RUN mkdir /app
WORKDIR /app

docker-compose.ymlの作成

Railsアプリケーションを構成するコンテナの情報を記述します。

docker-compose.yml

version: "3"

services:
  web:
    build: web
    ports:
      - "3000:3000"
    environment:
      - "DATABASE_HOST=db"
      - "DATABASE_PORT=5432"
      - "DATABASE_USER=postgres"
      - "DATABASE_PASSWORD=mysecretpassword1234"
    links:
      - db
    volumes:
      - "./app:/app" #共有フォルダの設定
    stdin_open: true

  db:
    image: postgres:10.1
    ports:
      - "5432:5432"
    environment:
      - "POSTGRES_USER=postgres"
      - "POSTGRES_PASSWORD=mysecretpassword1234"

コンテナを起動する

docker-compose build
docker-compose up -d

コンテナにログインする

docker-compose exec web bash

Railsアプリを作成する

コンテナの中で実行します。

rails new <アプリ名> -d postgresql -BT

DBをPostgreSQLに設定 (-d postgresql)
bundle installを省略　(-B)
テストファイルの作成を省略 (-T)

Gemfileを編集する

therubyracerのコメントを外します。

Gemfile

source 'https://rubygems.org'

git_source(:github) do |repo_name|
  repo_name = "#{repo_name}/#{repo_name}" unless repo_name.include?("/")
  "https://github.com/#{repo_name}.git"
end


# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '~> 5.1.4'
# Use postgresql as the database for Active Record
gem 'pg', '~> 0.18'
# Use Puma as the app server
gem 'puma', '~> 3.7'
# Use SCSS for stylesheets
gem 'sass-rails', '~> 5.0'
# Use Uglifier as compressor for JavaScript assets
gem 'uglifier', '>= 1.3.0'
# See https://github.com/rails/execjs#readme for more supported runtimes
gem 'therubyracer', platforms: :ruby

# Use CoffeeScript for .coffee assets and views
gem 'coffee-rails', '~> 4.2'
# Turbolinks makes navigating your web application faster. Read more: https://github.com/turbolinks/turbolinks
gem 'turbolinks', '~> 5'
# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
gem 'jbuilder', '~> 2.5'
# Use Redis adapter to run Action Cable in production
# gem 'redis', '~> 3.0'
# Use ActiveModel has_secure_password
# gem 'bcrypt', '~> 3.1.7'

# Use Capistrano for deployment
# gem 'capistrano-rails', group: :development

group :development, :test do
  # Call 'byebug' anywhere in the code to stop execution and get a debugger console
  gem 'byebug', platforms: [:mri, :mingw, :x64_mingw]
end

group :development do
  # Access an IRB console on exception pages or by using <%= console %> anywhere in the code.
  gem 'web-console', '>= 3.3.0'
  gem 'listen', '>= 3.0.5', '< 3.2'
  # Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
  gem 'spring'
  gem 'spring-watcher-listen', '~> 2.0.0'
end

# Windows does not include zoneinfo files, so bundle the tzinfo-data gem
gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]

config/database.ymlを編集する

PostgreSQLに接続できるように編集します。
defaultに下記項目の設定を追加します。

host
port
username
password

# PostgreSQL. Versions 9.1 and up are supported.
#
# Install the pg driver:
#   gem install pg
# On OS X with Homebrew:
#   gem install pg -- --with-pg-config=/usr/local/bin/pg_config
# On OS X with MacPorts:
#   gem install pg -- --with-pg-config=/opt/local/lib/postgresql84/bin/pg_config
# On Windows:
#   gem install pg
#       Choose the win32 build.
#       Install PostgreSQL and put its /bin directory on your path.
#
# Configure Using Gemfile
# gem 'pg'
#
default: &default
  adapter: postgresql
  encoding: unicode
  # For details on connection pooling, see Rails configuration guide
  # http://guides.rubyonrails.org/configuring.html#database-pooling
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
  host: <%= ENV.fetch('DATABASE_HOST') { 'localhost' } %>
  port: <%= ENV.fetch('DATABASE_PORT') { 5432 } %>
  username: <%= ENV.fetch('DATABASE_USER') { 'root' } %>
  password: <%= ENV.fetch('DATABASE_PASSWORD') { 'password' } %>

development:
  <<: *default
  database: <アプリ名>_development

  # The specified database role being used to connect to postgres.
  # To create additional roles in postgres see `$ createuser --help`.
  # When left blank, postgres will use the default role. This is
  # the same name as the operating system user that initialized the database.
  #username: <アプリ名>

  # The password associated with the postgres role (username).
  #password:

  # Connect on a TCP socket. Omitted by default since the client uses a
  # domain socket that doesn't need configuration. Windows does not have
  # domain sockets, so uncomment these lines.
  #host: localhost

  # The TCP port the server listens on. Defaults to 5432.
  # If your server runs on a different port number, change accordingly.
  #port: 5432

  # Schema search path. The server defaults to $user,public
  #schema_search_path: myapp,sharedapp,public

  # Minimum log levels, in increasing order:
  #   debug5, debug4, debug3, debug2, debug1,
  #   log, notice, warning, error, fatal, and panic
  # Defaults to warning.
  #min_messages: notice

# Warning: The database defined as "test" will be erased and
# re-generated from your development database when you run "rake".
# Do not set this db to the same as development or production.
test:
  <<: *default
  database: <アプリ名>_test

# As with config/secrets.yml, you never want to store sensitive information,
# like your database password, in your source code. If your source code is
# ever seen by anyone, they now have access to your database.
#
# Instead, provide the password as a unix environment variable when you boot
# the app. Read http://guides.rubyonrails.org/configuring.html#configuring-a-database
# for a full rundown on how to provide these environment variables in a
# production deployment.
#
# On Heroku and other platform providers, you may have a full connection URL
# available as an environment variable. For example:
#
#   DATABASE_URL="postgres://myuser:mypass@localhost/somedatabase"
#
# You can use this database configuration with:
#
#   production:
#     url: <%= ENV['DATABASE_URL'] %>
#
production:
  <<: *default
  database: <アプリ名>_production
  username: <アプリ名>
  password: <%= ENV['<アプリ名>_DATABASE_PASSWORD'] %>

Railsアプリを起動する

作成したアプリのディレクトリに移動します。
そしてbundle installの実行し、その後アプリを起動します。

ブラウザでlocalhost:3000を開き、
"Yay! You're on Rails" が表示されることを確認します。

cd <アプリ名>
bundle install
rails s -b 0.0.0.0 -d

テーブルを生成する

PostgreSQLとの接続に問題がなく、テーブルが生成されることを確認します。

rails db:create

以上で、Rails+PostgreSQL環境の構築は完了です。

さいごに

間違っている箇所がありましたら、訂正リクエスト等をしていただけると幸いです。

参考

https://qiita.com/pokohide/items/7397b92a188da841b435
https://www.gakusmemo.com/?p=962

Rails+PostgreSQLの環境をdocker-composeで作成する