MySQLに接続出来ないエラー

Question

前提・実現したいこと

Mysql2::Error::ConnectionError: Can't connect to MySQL server on '172.18.0.3' (115) のエラーを解決したい

Docker環境でRuby on RailsのDBを作成する為に

docker-compose run web rails db:create
```と入力すると上記のエラーが発生しました。

## 発生している問題・エラーメッセージ

Creating notworry_web_run ... done
Can't connect to MySQL server on '172.18.0.3' (115)
Couldn't create 'app_development' database. Please check your configuration.
rails aborted!
Mysql2::Error::ConnectionError: Can't connect to MySQL server on '172.18.0.3' (115)

/usr/local/bundle/gems/mysql2-0.5.3/lib/mysql2/client.rb:90:in connect' /usr/local/bundle/gems/mysql2-0.5.3/lib/mysql2/client.rb:90:in initialize'
/usr/local/bundle/gems/activerecord-6.0.3.4/lib/active_record/connection_adapters/mysql2_adapter.rb:24:in new' /usr/local/bundle/gems/activerecord-6.0.3.4/lib/active_record/connection_adapters/mysql2_adapter.rb:24:in mysql2_connection'
/usr/local/bundle/gems/activerecord-6.0.3.4/lib/active_record/connection_adapters/abstract/connection_pool.rb:887:in new_connection' /usr/local/bundle/gems/activerecord-6.0.3.4/lib/active_record/connection_adapters/abstract/connection_pool.rb:931:in checkout_new_connection'
/usr/local/bundle/gems/activerecord-6.0.3.4/lib/active_record/connection_adapters/abstract/connection_pool.rb:910:in try_to_checkout_new_connection' /usr/local/bundle/gems/activerecord-6.0.3.4/lib/active_record/connection_adapters/abstract/connection_pool.rb:871:in acquire_connection'
/usr/local/bundle/gems/activerecord-6.0.3.4/lib/active_record/connection_adapters/abstract/connection_pool.rb:593:in checkout' /usr/local/bundle/gems/activerecord-6.0.3.4/lib/active_record/connection_adapters/abstract/connection_pool.rb:437:in connection'
/usr/local/bundle/gems/activerecord-6.0.3.4/lib/active_record/connection_adapters/abstract/connection_pool.rb:1119:in retrieve_connection' /usr/local/bundle/gems/activerecord-6.0.3.4/lib/active_record/connection_handling.rb:221:in retrieve_connection'
/usr/local/bundle/gems/activerecord-6.0.3.4/lib/active_record/connection_handling.rb:189:in connection' /usr/local/bundle/gems/activerecord-6.0.3.4/lib/active_record/tasks/mysql_database_tasks.rb:8:in connection'
/usr/local/bundle/gems/activerecord-6.0.3.4/lib/active_record/tasks/mysql_database_tasks.rb:16:in create' /usr/local/bundle/gems/activerecord-6.0.3.4/lib/active_record/tasks/database_tasks.rb:126:in create'
/usr/local/bundle/gems/activerecord-6.0.3.4/lib/active_record/tasks/database_tasks.rb:185:in block in create_current' /usr/local/bundle/gems/activerecord-6.0.3.4/lib/active_record/tasks/database_tasks.rb:479:in block (2 levels) in each_current_configuration'
/usr/local/bundle/gems/activerecord-6.0.3.4/lib/active_record/tasks/database_tasks.rb:476:in each' /usr/local/bundle/gems/activerecord-6.0.3.4/lib/active_record/tasks/database_tasks.rb:476:in block in each_current_configuration'
/usr/local/bundle/gems/activerecord-6.0.3.4/lib/active_record/tasks/database_tasks.rb:475:in each' /usr/local/bundle/gems/activerecord-6.0.3.4/lib/active_record/tasks/database_tasks.rb:475:in each_current_configuration'
/usr/local/bundle/gems/activerecord-6.0.3.4/lib/active_record/tasks/database_tasks.rb:184:in create_current' /usr/local/bundle/gems/activerecord-6.0.3.4/lib/active_record/railties/databases.rake:39:in block (2 levels) in <main>'
/usr/local/bundle/gems/railties-6.0.3.4/lib/rails/commands/rake/rake_command.rb:23:in block in perform' /usr/local/bundle/gems/railties-6.0.3.4/lib/rails/commands/rake/rake_command.rb:20:in perform'
/usr/local/bundle/gems/railties-6.0.3.4/lib/rails/command.rb:48:in invoke' /usr/local/bundle/gems/railties-6.0.3.4/lib/rails/commands.rb:18:in <main>'
/usr/local/bundle/gems/bootsnap-1.7.0/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in require' /usr/local/bundle/gems/bootsnap-1.7.0/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in block in require_with_bootsnap_lfi'
/usr/local/bundle/gems/bootsnap-1.7.0/lib/bootsnap/load_path_cache/loaded_features_index.rb:92:in register' /usr/local/bundle/gems/bootsnap-1.7.0/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in require_with_bootsnap_lfi'
/usr/local/bundle/gems/bootsnap-1.7.0/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:31:in require' /app/bin/rails:9:in <top (required)>'
/usr/local/bundle/gems/spring-2.1.1/lib/spring/client/rails.rb:28:in load' /usr/local/bundle/gems/spring-2.1.1/lib/spring/client/rails.rb:28:in call'
/usr/local/bundle/gems/spring-2.1.1/lib/spring/client/command.rb:7:in call' /usr/local/bundle/gems/spring-2.1.1/lib/spring/client.rb:30:in run'
/usr/local/bundle/gems/spring-2.1.1/bin/spring:49:in <top (required)>' /usr/local/bundle/gems/spring-2.1.1/lib/spring/binstub.rb:11:in load'
/usr/local/bundle/gems/spring-2.1.1/lib/spring/binstub.rb:11:in <top (required)>' /app/bin/spring:15:in <top (required)>'
bin/rails:3:in load' bin/rails:3:in <main>'
Tasks: TOP => db:create
(See full trace by running task with --trace)

## 試したこと
1.docker-compose.yamlファイルのpasswordを設定

version: '3'

services:
web:
build: ./api
command: bundle exec rails s -p 3000 -b '0.0.0.0'
ports:
- '3000:3000'
depends_on:
- db
volumes:
- ./api:/app
- bundle:/usr/local/bundle
tty: true
stdin_open: true
db:
image: mysql:5.7
volumes:
- mysql_data:/var/lib/mysql/
environment:
MYSQL_ROOT_PASSWORD: 01110111
ports:
- '3306:3306'
front:
build: ./front
volumes:
- ./front:/app
- node_modules:/app/node_modules
ports:
- '8080:8080'
tty: true
stdin_open: true
command: npm run serve

volumes:
mysql_data:
bundle:
node_modules:

2.config/database.ymlのpassword、hostを変更

MySQL. Versions 5.5.8 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: utf8mb4
pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
username: root

• password:

• password: 01110111

• host: localhost

• host: 172.18.0.3

development:
<<: *default
database: app_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_test

As with config/credentials.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 https://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_production
username: app
password: <%= ENV['APP_DATABASE_PASSWORD'] %>

## 補足情報（FW/ツールのバージョンなど）
OS Catalina
バージョン10.15.7
MySQL 5.7
参考にしたサイト: [https://qiita.com/Kyou13/items/be9cdc10c54d39cded15](https://qiita.com/Kyou13/items/be9cdc10c54d39cded15)
##
5時間ほど調べてみましたが自力で解決できませんでした。
よろしくお願いします。

Answer 1

こんにちは。もし参考になりましたら。

docker-composeを使っていらっしゃるのであれば、docker compose側で各サービス（Rails, MySQL,フロントエンド用のNode.js）の名前解決ができるようになります。

※それぞれのコンテナ内からは、IPアドレスではなく、web,db, front で名前解決できます。

明示的にRails側の config/database.yml で host: 172.18.0.3 と記載されていますが、こちらではなくて、host: db としてみてはいかがでしょう。

また、設定を変更した上で、以下のコマンドでrailsのコンテナ内でMySQLのクライアントを起動できたりしますので、それで確認できると思います。

docker-compose run web rails dbconsole

https://railsguides.jp/command_line.html#rails-dbconsole

Comments

[Takum]

host: dbにしてみたところ、Created database 'app_development'と表示されました！ありがとうございます！
ただ、
docker-compose run web rails dbconsole
と入力したところ

Couldn't find database client: mysql, mysql5. Check your $PATH and try again.

と表示されたのですが、これはDBが作成できていないという事でしょうか。

[suama]

こんばんは、接続は大丈夫そうですね！
Created database 'app_development'　が出ていれば問題ないです！

> Couldn't find database client: mysql, mysql5.

こちらは接続確認用のものなので、Railsのコンテナ（動かしている環境）の中にMySQLのクライアントが入っていたらそれを起動する、というコマンドなのでできてなくても大丈夫です！（失礼しました）

[Takum]

わかりました！調べてみたらMySQLにクライアントツールがあるという事を理解したので、今後使う事があればインストールしてみようと思います。

[suama]

良かったです！
また、適切にエラーメッセージや設定ファイルを添えてくださっていたので、切り分けしやすく、こちらこそお役に立てて嬉しいです。