Pulling RDS config from an Elastic Beanstalk environment for Drupal

settings.php

<?php

// ---8<--- SNIP ---8<---

if (isset(
    $_SERVER['PARAM2'], $_SERVER['RDS_HOSTNAME'], $_SERVER['RDS_PORT'], $_SERVER['RDS_USERNAME'], $_SERVER['RDS_PASSWORD']
)) {
  $databases = array(
    'default' =>
    array(
      'default' =>
      array(
        'database' => $_SERVER['PARAM2'], // Set by you in the EB container
        'username' => $_SERVER['RDS_USERNAME'],
        'password' => $_SERVER['RDS_PASSWORD'],
        'host' => $_SERVER['RDS_HOSTNAME'],
        'port' => $_SERVER['RDS_PORT'],
        'driver' => 'mysql',
        'prefix' => '',
      ),
    ),
  );
} else {
  $databases = array(
    'default' =>
    array(
      'default' =>
      array(
        'database' => 'dev_db',
        'username' => 'dev_user',
        'password' => 'dev_password',
        'host' => 'localhost',
        'port' => '',
        'driver' => 'mysql',
        'prefix' => '',
      ),
    ),
  );
}

// ---8<--- SNIP ---8<---