dockerがrailsのコマンドを受け入れてくれないんです・・・助けてください・・

前提・実現したいこと

いつもお世話になっております。
今回もよろしくお願いいたします。
docker-composeで立ち上げたコンテナをVScodeの拡張機能remote-contaierを使って外部から扱いたいのですが、ConnectionErrorが出てしまい、railsがmysqlサーバーを認識してくれません
macを使っています

発生している問題・エラーメッセージ

yuzanoMacBook-puro:sample_app user$ rails db:migrate
rails aborted!
Mysql2::Error::ConnectionError: Unknown MySQL server host 'db' (0)
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/mysql2-0.5.2/lib/mysql2/client.rb:90:in `connect'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/mysql2-0.5.2/lib/mysql2/client.rb:90:in `initialize'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/activerecord-5.2.3/lib/active_record/connection_adapters/mysql2_adapter.rb:22:in `new'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/activerecord-5.2.3/lib/active_record/connection_adapters/mysql2_adapter.rb:22:in `mysql2_connection'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/activerecord-5.2.3/lib/active_record/connection_adapters/abstract/connection_pool.rb:811:in `new_connection'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/activerecord-5.2.3/lib/active_record/connection_adapters/abstract/connection_pool.rb:855:in `checkout_new_connection'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/activerecord-5.2.3/lib/active_record/connection_adapters/abstract/connection_pool.rb:834:in `try_to_checkout_new_connection'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/activerecord-5.2.3/lib/active_record/connection_adapters/abstract/connection_pool.rb:795:in `acquire_connection'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/activerecord-5.2.3/lib/active_record/connection_adapters/abstract/connection_pool.rb:523:in `checkout'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/activerecord-5.2.3/lib/active_record/connection_adapters/abstract/connection_pool.rb:382:in `connection'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/activerecord-5.2.3/lib/active_record/connection_adapters/abstract/connection_pool.rb:1014:in `retrieve_connection'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/activerecord-5.2.3/lib/active_record/connection_handling.rb:118:in `retrieve_connection'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/activerecord-5.2.3/lib/active_record/connection_handling.rb:90:in `connection'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/activerecord-5.2.3/lib/active_record/tasks/database_tasks.rb:172:in `migrate'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/activerecord-5.2.3/lib/active_record/railties/databases.rake:60:in `block (2 levels) in <main>'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/railties-5.2.3/lib/rails/commands/rake/rake_command.rb:23:in `block in perform'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/railties-5.2.3/lib/rails/commands/rake/rake_command.rb:20:in `perform'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/railties-5.2.3/lib/rails/command.rb:48:in `invoke'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/railties-5.2.3/lib/rails/commands.rb:18:in `<main>'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/bootsnap-1.4.4/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in `require'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/bootsnap-1.4.4/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in `block in require_with_bootsnap_lfi'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/bootsnap-1.4.4/lib/bootsnap/load_path_cache/loaded_features_index.rb:92:in `register'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/bootsnap-1.4.4/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:21:in `require_with_bootsnap_lfi'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/bootsnap-1.4.4/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:30:in `require'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/activesupport-5.2.3/lib/active_support/dependencies.rb:291:in `block in require'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/activesupport-5.2.3/lib/active_support/dependencies.rb:257:in `load_dependency'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/activesupport-5.2.3/lib/active_support/dependencies.rb:291:in `require'
bin/rails:4:in `<main>'
Tasks: TOP => db:migrate
(See full trace by running task with --trace)
yuzanoMacBook-puro:sample_app user$ rails db:migrate
rails aborted!
Mysql2::Error::ConnectionError: Unknown MySQL server host 'db' (0)
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/mysql2-0.5.2/lib/mysql2/client.rb:90:in `connect'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/mysql2-0.5.2/lib/mysql2/client.rb:90:in `initialize'

/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/activesupport-5.2.3/lib/active_support/dependencies.rb:291:in `block in require'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/activesupport-5.2.3/lib/active_support/dependencies.rb:257:in `load_dependency'
/Users/user/workspace/sample_app/vendor/bundle/ruby/2.6.0/gems/activesupport-5.2.3/lib/active_support/dependencies.rb:291:in `require'
bin/rails:4:in `<main>'
Tasks: TOP => db:migrate
(See full trace by running task with --trace)``

該当のソースコード

app/config/database.yml

# MySQL. Versions 5.1.10 and up are supported.
#
# Install the MySQL driver
#   gem install mysql2
#
# Ensure the MySQL gem is defined in your Gemfile
#   gem 'mysql2'
#
# And be sure to use new-style password hashing:
#   https://dev.mysql.com/doc/refman/5.7/en/password-hashing.html
#
default: &default
  adapter: mysql2
  encoding: utf8
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
  username: root
  password: password
  host: db

development:
  <<: *default
  database: app_name_development

# 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: app_name_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="mysql2://myuser:mypass@localhost/somedatabase"
#
# You can use this database configuration with:
#
#   production:
#     url: <%= ENV['DATABASE_URL'] %>
#
production:
  <<: *default
  database: app_name_production
  username: app_name
  password: <%= ENV['APP_NAME_DATABASE_PASSWORD'] %>

docker-compose.yml

version: '3'
services:
  db:
    image: mysql:5.7
    environment:
      MYSQL_ROOT_PASSWORD: password
      MYSQL_DATABASE: root
    ports:
      - "3306:3306"

  web:
    build: .
    command: bundle exec rails s -p 3000 -b '0.0.0.0'
    volumes:
      - .:/app_name
    ports:
      - "3000:3000"
    links:
      - db:mysql

Dockerfile

# コピペでOK, app_nameもそのままでOK
# 19.01.20現在最新安定版のイメージを取得
FROM ruby:2.5.3

# 必要なパッケージのインストール（基本的に必要になってくるものだと思うので削らないこと）
RUN apt-get update -qq && \
    apt-get install -y build-essential \ 
                       libpq-dev \        
                       nodejs           

# 作業ディレクトリの作成、設定
RUN mkdir /app_name 
##作業ディレクトリ名をAPP_ROOTに割り当てて、以下$APP_ROOTで参照
ENV APP_ROOT /app_name 
WORKDIR $APP_ROOT

# ホスト側（ローカル）のGemfileを追加する（ローカルのGemfileは【３】で作成）
ADD ./Gemfile $APP_ROOT/Gemfile
ADD ./Gemfile.lock $APP_ROOT/Gemfile.lock

# Gemfileのbundle install
RUN bundle install
ADD . $APP_ROOT

退会済みユーザー

2019/08/09 08:35

前の質問はどうなったのでしょうか？追記依頼放置されているようですが

k_yusuke

2019/08/10 11:19

dyoshikawa様返信ありがとうございます！すみません！質問に反応できていませんでした。。。まだ未解決のままです！遅くなってしまったのですが追記させていただきました。知らせていただき助かりました！ありがとうございます！

行動規範の内容に同意します

回答1件

rails の設定では host: db となっていて db という名前のサーバーにアクセスしようとしていますが、

docker-compose.yml では

    links:
      - db:mysql

となっているので、 dbのコンテナは mysql というホスト名で参照される設定になっているように見えます。

    links:
      - db

とかにしたら、何か変わるのではないでしょうか？

投稿2019/08/10 06:16

mokemokechicken

総合スコア948

k_yusuke

2019/08/10 11:23

mokemokeshicken様返信ありがとうございます。教えていただいたように、linksの表記を変更してみたのですが、エラーメッセージは前と変更ありませんでした。。　謎です。。他に質問文に追記しておくべきファイルなどあればどんどんおっしゃってくださいませ！！

mokemokechicken

2019/08/10 12:50

あー、これは、Dockerのホスト(Mac)から、Dockerの中のdbにアクセスしようとしているんですかね？

k_yusuke

2019/08/11 06:20

すみません、理解が追い付けてないんですがそうだと思います。。 dockerがDBを探し切れていないかなと判断しまして、 https://qiita.com/chorome/items/14dde59e960c0b35d8a0 の記事を参考にそのような記載にしていました。。 ※指摘いただいた箇所のみ以外は https://qiita.com/azul915/items/5b7063cbc80192343fc0 からコピペをしています

行動規範の内容に同意します