Connection Drupal website with SQL Google cloud database

I can`t find too much documentation about connecting Drupal7 website with SQL Google database. Does anybody have experience with it? I trying to split Drupal website on VM instance and mysql database on SQL Google storage. After that, change settings.php in Drupal:

$databases['default']['default'] = array(
'database' => 'DATABASE',
'username' => 'USERNAME',
'password' => 'PASSWORD',
'host' => 'Public_IP_of_Google_SQL',
'driver' => 'mysql',
'port' => 3306 (I try 1433 also),
'prefix' => '',

); }

On SQL instance I have enabled firewall for tcp ports:3306,1433

However, I always get error PDOException: SQLSTATE[HY000] [2002] Connection refused in lock_may_be_available() (line 167 of /home/public_html/includes/lock.inc).

Can anybody help? What can I do on Drupal side to connect website with external database?