PHP local host to URL - php

Question

I've set up a local web server on my home network by setting up a LAMP on my Raspberry Pi. When doing my PHP scripts and connecting to MySQL database I have been using localhost. Now I'm messing about with accessing the server outside of my home network so I've set-up a domain name to access the server.
But what I didn't realise is my code still uses the localhost to log into the MySQL database. So I decided to change it to my domain name and now it states that the database cannot be found so I'm assuming it is not logging on and therefore no database is being selected.
PHP Script:
<?php
//thermReading1.php
$servername = "myservername.com"; //example URL
$username = "user";
$password = "password";
$dbname = "database";
//create connection
$db_handle = mysql_connect($servername,$username,$password);
$db_found = mysql_select_db($dbname,$db_handle);
$thermID = "'T00'";
$userID = "'1'";
if($db_found)
{
$sql = "SELECT * FROM tblTempReading"
$result = mysql_query($sql);
while($db_field = mysql_fetch_assoc($result))
{
echo "<p>" . $db_field['temp'] . "°C</p>";
echo "<p>" . $db_field['tempTimeStamp'] . "</p>";
}
}
else
{
echo "<p>Database NOT Found</p>";
}//endif
mysql_close($db_handle);
?>
Is this a problem with logging into MySQL via the server instead of localhost or would it be firewall issues (I've set up port forwarding on my router to access the server)?
Any help is appreciated, I'm new to this web server stuff.

Answer 1

localhost is a domain name to refer to the local machine.
If the web server and the MySQL database server are on the same server, you can leave localhost as "remote" database host.
In fact, when you're running a script on a server, all addresses that have to be resolved from DNS are solved from internal DNS server and not from the client DNS.
It does not matter from where you make the request to the server. If the IP address of the machine that runs PHP is the same of the database server, the address of the database server is localhost, relative to the web server.