You need to tell mysqli to throw exceptions:
mysqli_report(MYSQLI_REPORT_STRICT);
try {
$connection = new mysqli('localhost', 'my_user', 'my_password', 'my_db') ;
} catch (Exception $e ) {
echo "Service unavailable";
echo "message: " . $e->message; // not in live code obviously...
exit;
}
Now you will catch the exception and you can take it from there.