Hello all,
I completed a website (it was code by php) and putted it to AWS, I install fedora instance in EC2 with the base is php and mysql.
I putted all files of my website to folder /home/webuser/helloworld/htddocs and my database (mysql) to folder /var/lib/mysql/test ("test" is my database's name).
I connect to database by a php file that is successful and its code is:

<?php # mysql_connect.php 
DEFINE ('DB_USER', 'root'); 
DEFINE ('DB_PASSWORD', 'ab2345'); 
DEFINE ('DB_HOST', 'root@localhost'); 
DEFINE ('DB_NAME', 'test'); 
# Connect to MYSQL 
$dbc = @mysql_connect (DB_HOST, DB_USER, DB_PASSWORD) OR die ('Could not connect to MYSQL:' .mysql_error()); 
mysql_select_db (DB_NAME) OR die ('Could not select the database:' .mysql_error()); 
?>

What does the php.errors log file say about this?

Try change:

DEFINE('DB_HOST', 'root@localhost');

DEFINE('DB_HOST', 'localhost');

Could not connect to MYSQL:Unknown MySQL server host 'root@localhost' (1)