【rails + docker】 bin/rails db:create 実行時エラーについて

Question

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

# 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'] %>

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

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

Answer 1

could not translate host name "db" to address: Name does not resolve
は db というホストが見つかりませんという趣旨です。

host: db

Railsからはdockerで設定したリンク（ホスト）が見えません。なので、環境変数を経由して伝えます。
例えば
docker-compose.ymlに次のように追加し

environment:
  - DATABASE_HOST=db
  - DATABASE_PORT=5432

database.ymlに次のように追加します

default: &default
  adapter: postgresql
  encoding: unicode
  host: <%= ENV.fetch('DATABASE_HOST') { 'localhost' } %>
  port: <%= ENV.fetch('DATABASE_PORT') { 5432 } %>

Comments

[yodev21]

アドバイスありがとうございました！