parameters:
    database_driver:   pdo_mysql
    database_host:     127.0.0.1
    database_port:     ~
    database_name:     database_example_name
    database_user:     example_username
    database_password: ****

SQLSTATE[28000] [1045] Access denied for user 'example_username'@'localhost' (using password: NO)

(...)
return $this->services['doctrine.dbal.default_connection'] = $this->get('doctrine.dbal.connection_factory')->createConnection(array('host' => 'localhost', 'port' => NULL, 'user' => 'root', 'password' => NULL, 'driver' => 'pdo_mysql', 'driverOptions' => array()), $b, $c, array());
(...)

setsebool -P httpd_can_network_connect=1
setsebool -P httpd_can_network_connect_db=1

database_driver: pdo_mysql
database_host: 127.0.0.1
database_port: null
database_name: database_name
database_user: username
database_password: password