php - Unable to connect to Amazon RDS from EC2 wordpress site -

i'm migrating website cpanel hosting amazon ec2. i'm using amazon rds host wordpress database.

i followed following steps:

1. created folder wordpress files old server.
2. created database in rds , uploaded old site's db dump.
3. edited wp-config.php file change parameters connect rds instance.

while worked out fine, except i'm getting following error "error establishing database connection" while open site in browser. tried changing security group on rds , allow , added user on mysql required permission database.

the problem connection rds not getting established. i'm able connect rds ec2 instance wordpress not able to.

my wp-config.php looks like:

/** name of database wordpress */ define('db_name', 'wordpress');  /** mysql database username */ define('db_user', 'db_username');  /** mysql database password */ define('db_password', 'db_password');  /** mysql hostname */ define('db_host', 'wordpress-site.something.rds.amazonaws.com:3306');  /** database charset use in creating database tables. */ define('db_charset', 'utf8');  /** database collate type. don't change if in doubt. */ define('db_collate', ''); 

edit: changed localhost's wp-config.php point rds , site working fine on localhost. problem connection issues ec2.

go aws settings , have see ports have open. iirc, shut, have open port db.