could not translate host name "db" to address: Name or service not known が解決できない

Question

docker-composeを用いたdb:createコマンドを実行しようとしていたのですが、下記のエラー分が発生してしまい、解消できずに困っております。

could not translate host name "db" to address: Name or service not known
Couldn't create database for {"adapter"=>"postgresql", "encoding"=>"unicode", "host"=>"db", "username"=>"postgres", "password"=>nil, "pool"=>5, "database"=>"myapp_development"}
rake aborted!

【エラーログ】
db_1 | Error: Database is uninitialized and superuser password is not specified.
db_1 | Error: Database is uninitialized and superuser password is not specified.
db_1 | You must specify POSTGRES_PASSWORD to a non-empty value for the
db_1 | superuser. For example, "-e POSTGRES_PASSWORD=password" on "docker run".
db_1 |
db_1 | You may also use "POSTGRES_HOST_AUTH_METHOD=trust" to allow all
db_1 | connections without a password. This is not recommended.
db_1 |
db_1 | See PostgreSQL documentation about "trust":
db_1 | https://www.postgresql.org/docs/current/auth-trust.html

下記の記事通りにdocker-compose.ymlにPOSTGRES_HOST_AUTH_METHOD=trustを定義してあげたのですがエラーが解消されません。
【PostgreSQL（Docker）にRails（Docker）が接続できなくなったから調べてみた。】
https://qiita.com/at-946/items/2fb75cec5355fad4050d

なぜなのでしょうか・・・？

以下コードです。
ご指南のほど何卒よろしくお願いいたします。

【dartabase.yml】

#
# 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
  host: db
  username: postgres

  # For details on connection pooling, see rails configuration guide
  # http://guides.rubyonrails.org/configuring.html#database-pooling
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>

development:
  <<: *default
  database: myapp_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: myapp

  # 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: myapp_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: myapp_production
  username: myapp
  password: <%= ENV['MYAPP_DATABASE_PASSWORD'] %>

【docker-compose.yml】

services:
  db:
    image: postgres
    environment:
      - POSTGRES_HOST_AUTH_METHOD=trust
  web:
    build: .
    command: bundle exec rails s -p 3000 -b '0.0.0.0'
    volumes:
      - .:/myapp
    ports:
      - "3000:3000"
    depends_on:
      - db

Answer 1

既に「db」サービス用のボリューム（ /var/lib/postgresql/data）が作成済みの状態としても、後から docker-compose.yaml を今回のように編集されたら、通常は db サービスが起動すると思います。私の環境でも試しましたが docker-compose ps を実行すると、「db」サービスは正常に起動しています。

下記の記事通りにdocker-compose.ymlにPOSTGRES_HOST_AUTH_METHOD=trustを定義してあげたのですがエラーが解消されません。

エラー解消のための設定としては、こちらで問題無いはずです。

念のため、現在の docker-compose.yaml ファイルがあるディレクトリとは別の場所で、docker-compose up -d を試みてみると、データベースは真っ新な状態から実行されますので、正常に処理ができるでしょう。

また、エラー could not translate host name "db" to address: Name or service not known に関しても、当初は db サービス（postgres）が起動できなかったから出ていたエラーであり、正常に起動できる設定であれば、こちらのエラーの解消も期待できます。