我是使用docker的新手，我的问题是使用mysql和docker加载一个带有环境变量的Rails4应用程序。
基本上，我构建应用程序并运行它。在另一个终端中，我创建mysql数据库和database.yml使用的user/password。以下是我运行的步骤：

$ docker-compose build
$ docker-compose up -d
$ docker exec -it poseidon_db_1 bash -l

# root@dockerimg mysql -uroot -proot

mysql> create database poseidon_development;
mysql> CREATE USER 'poseidon_user'@'localhost' IDENTIFIED BY 'poseidon_password';
mysql> CREATE USER 'poseidon_user'@'%' IDENTIFIED BY 'poseidon_password';
mysql> GRANT ALL ON poseidon_development.* TO 'poseidon_user'@'localhost';
mysql> GRANT ALL ON poseidon_development.* TO 'poseidon_user'@'%';
mysql> FLUSH PRIVILEGES;
mysql> exit

# root@dockerimg exit

$ docker-compose run web bundle exec rake db:migrate

数据库.yml

default: &default
  adapter: mysql2
  encoding: utf8
  pool: 5
  username: <%= ENV["DATABASE_USERNAME"] %>
  password: <%= ENV["DATABASE_PASSWORD"] %>
  database: <%= ENV["DATABASE_NAME"] %>
  host: db

development:
  <<: *default

test:
  <<: *default

docker-compose.yml公司

version: '3.6'

services:
  db:
    restart: always
    image: mysql:5.6.34
    ports:
      - "3306:3306"
    volumes:
      - dbdata
    env_file:
      - .env

  dbdata:
    image: tianon/true
    volumes:
      - /var/lib/mysql

  web:
    build: .
    ports:
      - '3000:3000'
    volumes:
      - webdata
    links:
      - "db"
    env_file:
      - .env

  webdata:
    image: tianon/true
    volumes:
      - ".:/var/www/poseidon"

dockerfile文件

FROM ruby:2.3.7

ENV LANG C.UTF-8

RUN apt-get update -qq
RUN apt-get install -y build-essential mysql-client vim

WORKDIR /tmp
ADD Gemfile Gemfile
ADD Gemfile.lock Gemfile.lock
RUN bundle install

ENV APP_ROOT /var/www/poseidon

RUN mkdir -p $APP_ROOT
WORKDIR $APP_ROOT
COPY . $APP_ROOT
RUN chmod a+x .env

EXPOSE 3000

ENTRYPOINT ["bundle", "exec"]

CMD ["rails", "server", "-p", "3000", "-b", "0.0.0.0"]

.环境

SECRET_KEY_BASE=xxxxxxxx
RAILS_ENV=development
RAILS_SERVE_STATIC_FILES=true
URL_OPTIONS=domain.com
RECAPTCHA_SECRET_KEY=xxxxxxx
RECAPTCHA_SITE_KEY=xxxxxxx
MAILGUN_API=xxxxxx
MAILGUN_DOMAIN=xxxxxxx
MYSQL_ROOT_PASSWORD=root
DATABASE_USERNAME=poseidon_user
DATABASE_PASSWORD=poseidon_password
DATABASE_NAME=poseidon_development

问题是，当访问 http://127.0.0.1 ，我收到 Access denied for user '<%= ENV["DATABASE_USERNAME"] %>'@'IP' (using password: YES) 我不知道该怎么做了，它似乎没有加载环境变量正确。
任何帮助都将不胜感激！
当做