Please help me out !

Hello Please hear me and try to help me out, I am a PHP programmer, I know PHP for websites that can be hosted on one server Buy I don't know how to work with PHP on website that has more than one server So I am trying to find out where I could learn about all the subjects that are related to Building a large web application - a website that has multiple servers and doesn't rely one one server only The reason behind this is that one server written with PHP will likely go down if number of users exceeds the limit So I don't know what to do, where I can learn all the subjects (PHP,DATABASE,THE RIGHT DESIGN ETC ..)that are related to that Do you know what eBooks out there or web links or any source of information that can help ? Websites like facebook,twitter,reddit, are built like that, how could I learn that ? Please do your best effort to help me out, I have a cool idea that I want to develop, Thank you !!!