How to seperate web servers and Database servers?

Question

In the application running in one particular web server and fetching data in the other database servers.
In the sense both machines running seperately..

Answer 1

Its perfectly possible,

Suppose you have a MYSQL server and another server running Apache httpd. Then you need to configure the mysql to allow the IP of the httpd machine to have access. And from apache it it just providing the IP of the machine of the MySql server.

Steps on machine where MySql Server is running

$ FLUSH PRIVILEGES;
$ GRANT ALL PRIVILEGES ON *.* TO  'username'@'X.X.X.X'  IDENTIFIED  BY  'mypassword';
Where X.X.X.X is the IP of the machine where apache is running.

Now on Apache or PHP in place of 127.0.0.1 you will provide the IP of the MySql Server machine and login and password as you have provided in the above steps.

Answer 2

Just addition to what Salil suggested,
You just need to grant PRIVILEGES to the username@ipaddress identified by the and you are done.