AWS: Not able to connect to mysql(rds) from wordpress

I'm trying to connect to mysql instance on rds via worpress, but I get this error:

Warning: mysql_connect(): Unknown MySQL server host '***********************' (111) in /var/www/html/wp-includes/wp-db.php on line 1568

Error establishing a database connection...

As I have read, (111) is for permission error. But I'm able to connect to the instance via workbench. In fact I was able to connect via wordpress earlier too.

This is driving me crazy. Please help. (My wp-config.php is correct. Checked it a 1000 times)