### 前提・実現したいこと

Ruby on Rails6 実践ガイドの書籍を用いてDockerでRuby on Railsの環境構築をしたいです。  
以下のコマンドを実行するとエラーが出て、データベースに接続されないようです。解決策をお教え下さい。

### 発生している問題・エラーメッセージ

```

    bash-4.4$ bin/rails db:create
    could not translate host name "db" to address: Name does not resolve
    Couldn't create 'baukis2_development' database. Please check your configuration.
    rails aborted!
    PG::ConnectionBad: could not translate host name "db" to address: Name does not resolve
    /usr/local/bundle/gems/pg-1.2.3/lib/pg.rb:58:in `initialize'
    /usr/local/bundle/gems/pg-1.2.3/lib/pg.rb:58:in `new'
    /usr/local/bundle/gems/pg-1.2.3/lib/pg.rb:58:in `connect'
    /usr/local/bundle/gems/activerecord-6.0.2.2/lib/active_record/connection_adapters/postgresql_adapter.rb:46:in `postgresql_connection'
    /usr/local/bundle/gems/activerecord-6.0.2.2/lib/active_record/connection_adapters/abstract/connection_pool.rb:889:in `new_connection'
    /usr/local/bundle/gems/activerecord-6.0.2.2/lib/active_record/connection_adapters/abstract/connection_pool.rb:933:in `checkout_new_connection'
    /usr/local/bundle/gems/activerecord-6.0.2.2/lib/active_record/connection_adapters/abstract/connection_pool.rb:912:in `try_to_checkout_new_connection'
    /usr/local/bundle/gems/activerecord-6.0.2.2/lib/active_record/connection_adapters/abstract/connection_pool.rb:873:in `acquire_connection'
    /usr/local/bundle/gems/activerecord-6.0.2.2/lib/active_record/connection_adapters/abstract/connection_pool.rb:595:in `checkout'
    /usr/local/bundle/gems/activerecord-6.0.2.2/lib/active_record/connection_adapters/abstract/connection_pool.rb:439:in `connection'
    /usr/local/bundle/gems/activerecord-6.0.2.2/lib/active_record/connection_adapters/abstract/connection_pool.rb:1121:in `retrieve_connection'
    /usr/local/bundle/gems/activerecord-6.0.2.2/lib/active_record/connection_handling.rb:238:in `retrieve_connection'
    /usr/local/bundle/gems/activerecord-6.0.2.2/lib/active_record/connection_handling.rb:206:in `connection'
    /usr/local/bundle/gems/activerecord-6.0.2.2/lib/active_record/tasks/postgresql_database_tasks.rb:12:in `connection'
    /usr/local/bundle/gems/activerecord-6.0.2.2/lib/active_record/tasks/postgresql_database_tasks.rb:21:in `create'
    /usr/local/bundle/gems/activerecord-6.0.2.2/lib/active_record/tasks/database_tasks.rb:126:in `create'
    /usr/local/bundle/gems/activerecord-6.0.2.2/lib/active_record/tasks/database_tasks.rb:185:in `block in create_current'
    /usr/local/bundle/gems/activerecord-6.0.2.2/lib/active_record/tasks/database_tasks.rb:479:in `block (2 levels) in each_current_configuration'
    /usr/local/bundle/gems/activerecord-6.0.2.2/lib/active_record/tasks/database_tasks.rb:476:in `each'
    /usr/local/bundle/gems/activerecord-6.0.2.2/lib/active_record/tasks/database_tasks.rb:476:in `block in each_current_configuration'
    /usr/local/bundle/gems/activerecord-6.0.2.2/lib/active_record/tasks/database_tasks.rb:475:in `each'
    /usr/local/bundle/gems/activerecord-6.0.2.2/lib/active_record/tasks/database_tasks.rb:475:in `each_current_configuration'
    /usr/local/bundle/gems/activerecord-6.0.2.2/lib/active_record/tasks/database_tasks.rb:184:in `create_current'
    /usr/local/bundle/gems/activerecord-6.0.2.2/lib/active_record/railties/databases.rake:39:in `block (2 levels) in <main>'
    /usr/local/bundle/gems/railties-6.0.2.2/lib/rails/commands/rake/rake_command.rb:23:in `block in perform'
    /usr/local/bundle/gems/railties-6.0.2.2/lib/rails/commands/rake/rake_command.rb:20:in `perform'
    /usr/local/bundle/gems/railties-6.0.2.2/lib/rails/command.rb:48:in `invoke'
    /usr/local/bundle/gems/railties-6.0.2.2/lib/rails/commands.rb:18:in `<main>'
    /usr/local/bundle/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in `require'
    /usr/local/bundle/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in `block in require_with_bootsnap_lfi'
    /usr/local/bundle/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/loaded_features_index.rb:92:in `register'
    /usr/local/bundle/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in `require_with_bootsnap_lfi'
    /usr/local/bundle/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:31:in `require'
    /usr/local/bundle/gems/activesupport-6.0.2.2/lib/active_support/dependencies.rb:325:in `block in require'
    /usr/local/bundle/gems/activesupport-6.0.2.2/lib/active_support/dependencies.rb:291:in `load_dependency'
    /usr/local/bundle/gems/activesupport-6.0.2.2/lib/active_support/dependencies.rb:325:in `require'
    /apps/baukis2/bin/rails:9:in `<top (required)>'
    /usr/local/bundle/gems/spring-2.1.0/lib/spring/client/rails.rb:28:in `load'
    /usr/local/bundle/gems/spring-2.1.0/lib/spring/client/rails.rb:28:in `call'
    /usr/local/bundle/gems/spring-2.1.0/lib/spring/client/command.rb:7:in `call'
    /usr/local/bundle/gems/spring-2.1.0/lib/spring/client.rb:30:in `run'
    /usr/local/bundle/gems/spring-2.1.0/bin/spring:49:in `<top (required)>'
    /usr/local/bundle/gems/spring-2.1.0/lib/spring/binstub.rb:11:in `load'
    /usr/local/bundle/gems/spring-2.1.0/lib/spring/binstub.rb:11:in `<top (required)>'
    /apps/baukis2/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)
    
```

### 該当のソースコード

database.yml

```

    # PostgreSQL. Versions 9.3 and up are supported.
    #
    # Install the pg driver:
    #   gem install pg
    # On macOS with Homebrew:
    #   gem install pg -- --with-pg-config=/usr/local/bin/pg_config
    # On macOS 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
      # https://guides.rubyonrails.org/configuring.html#database-pooling
      pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
      host: db
      username: postgres
      password: ""
    
    development:
      <<: *default
      database: baukis2_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: baukis2
    
      # 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: baukis2_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="postgres://myuser:mypass@localhost/somedatabase"
    #
    # You can use this database configuration with:
    #
    #   production:
    #     url: <%= ENV['DATABASE_URL'] %>
    #
    production:
      <<: *default
      database: baukis2_production
      username: baukis2
      password: <%= ENV['BAUKIS2_DATABASE_PASSWORD'] %>
    
    
```

docker-compose.yml

```

    version: '3'
    services:
      db:
        image: postgres:11.2-alpine
        volumes:
          - ./tmp/db:/var/lib/postgresql/data
      web:
        build: .
        command: /bin/sh
        environment:
          WEBPACKER_DEV_SERVER_HOST: "0.0.0.0"
          RAILS_SERVE_STATIC_FILES: "1"
          EDITOR: "vim"
        volumes:
          - ./apps:/apps
        ports:
          - "3000:3000"
          - "3035:3035"
        depends_on:
          - db
        tty: true
    
    
```

Dockerfile

```

    FROM oiax/rails6-deps:latest
    
    ARG UID=1000
    ARG GID=1000
    
    RUN mkdir /var/mail
    RUN groupadd -g $GID devel
    RUN useradd -u $UID -g devel -m devel
    RUN echo "devel ALL=(ALL) NOPASSWD:ALL" >> /etc/sudoers
    
    WORKDIR /tmp
    COPY init/Gemfile /tmp/Gemfile
    COPY init/Gemfile.lock /tmp/Gemfile.lock
    RUN bundle install
    
    COPY ./apps /apps
    
    RUN apk add --no-cache openssl
    
    USER devel
    
    RUN openssl rand -hex 64 > /home/devel/.secret_key_base
    RUN echo $'export SECRET_KEY_BASE=$(cat /home/devel/.secret_key_base)' \
      >> /home/devel/.bashrc
    
    WORKDIR /apps
    
```

### 試したこと

  1. `docker-compose run web rails db:create` を実行したが、変化はなかった。
  2. config/database.ymlのuserをrootにし、実行したが、変化はなかった。
  3. config/database.ymlのhostをlocalhostにし、実行したが、変化はなかった。

postgresqlのプロセスを確認したところ  
存在していなかった

```

    ps -ef | grep ps -ef | grep post
    devel     1407  1333  0 09:46 pts/1    00:00:00 grep post
    
```

postgresqlに関するディレクトリが存在するか確認したところ複数件ヒットした。  
しかし、どのようにしてサービスのステータスを確認および、起動させるかわからず調査中。

```

    find / -type f | xargs grep postgres
    
```
CC BY-SA 4.0
2020-04-25T09:54:45.850
65951
2022-05-09T11:05:35.657
2020-04-25T11:26:10.943
3060
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question
ruby-on-rails ruby docker docker-compose docker-for-mac
docker-composeでのRuby on Rails環境構築でPostgreSQLに接続できない
> could not translate host name "db" to address: Name does not resolve

とあるので、Docker内部DNSの名前解決ができていないように見えます。  
アプリケーションのコンテナの中から ping db などは通りますか？
CC BY-SA 4.0
2020-04-25T10:38:26.973
65952
2020-04-25T10:38:26.973
21329
65951
answer