$dsn = getenv('MYSQL_DSN');
$user = getenv('MYSQL_USER');
$password = getenv('MYSQL_PASSWORD');
try {
    $db = new PDO($dsn, $user, $password);
    $statement = $db->prepare("SELECT * from user");
    $statement->execute();
    $users = $statement->fetchAll();
} catch (Exception $e) {
    echo 'Caught exception: ',  $e->getMessage(), "n";
}

runtime: php
env: flex

runtime_config:
    document_root: .

env_variables:
    MYSQL_DSN: mysql:dbname=DATABASE;unix_socket=/cloudsql/CONNECTION_NAME
    MYSQL_USER: username
    MYSQL_PASSWORD: password