php - Amazon EC2 Connects to RDS from command line but not from web server

If have an amazon ec2 instance running php 5.5 and apache2. I am connecting to my RDS database using a simple test.php script. When I run the script as ec2-user or as root I am able to get a connection. When I run the same script via my webserver I get

Connection Can't connect to MySQL server on 'ip' (13).

I've tried the public and private IP addresses. This script does work from my other, non-amazon, webservers running the same php and apache. Not sure what to look at next since it works on the command line. Here's the example of the test.php script, pretty straight forward.

define("DB_IP”,”ip”);
define("DB_USERNAME”,”username”);
define("DB_PASSWORD”,”password”);
define("DB_DATABASE”,”database”);

echo "Connecting...\n";
$conn = new mysqli(DB_IP, DB_USERNAME, DB_PASSWORD, DB_DATABASE, 3306);

// Check connection
if ($conn->connect_error) {
   die(date('H:i:s')." Connection " . $conn->connect_error);
} 
echo date('H:i:s')." Connected successfully\n";
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Why would the connection work on the command line but not work when called from the web server?