Database settings for Drupal 6/7/8 fo use with Docker with linked database

settings.php

<?php

//...

$databases = array ();

$databases['default']['default'] = array(
  'driver' => 'mysql',
  'database' => getenv('DB_ENV_MYSQL_DATABASE'),
  'username' => getenv('DB_ENV_MYSQL_USER'),
  'password' => getenv('DB_ENV_MYSQL_PASSWORD'),
  'host' => getenv('DB_PORT_3306_TCP_ADDR'),
  'port' => getenv('DB_PORT_3306_TCP_PORT'),
  'prefix' => '',
  'collation' => 'utf8_general_ci',
);

//...