Q:

Error establishing a database connection : wordpress googleappengine cloudsql

I have DB connection error with ClouSQL. The details seems to be right. 
Error establishing a database connection
Below is my connection details.
 define('DB_HOST', ':/cloudsql/xxx-wp:wordpress');
  define('DB_USER', 'root');
  define('DB_PASSWORD', '');

I am stuck with this for couple of days now, no clue what the reason. It works fine with my local.
When I try wordpress admin console, it displays this message. Here my connection details and all the scenarios mentioned here seem to be ok.

This either means that the username and password information in your
  wp-config.php file is incorrect or we can't contact the database
  server at :/cloudsql/vairagyawp:wordpress. This could mean your host's
  database server is down.
Are you sure you have the correct username and password? 
  Are you sure that you have typed the correct hostname? 
  Are you sure that the database server is running?

Can you please clarify what the wordpress stands for in the DB_HOST detail. Is this CloudSQL instance name ?

A:

Found the reason, Cloud SQL Second Generation  is still in beta. Doesn't support App Engine. Its there in the dropdown, check the attached screenshot. 

