Here is an interesting article that describes private cloud architecture within LinkedIn. All the required tooling along with infrastructure has been done by them internally. Summary of what they wanted to achieve in 2009 :
LinkedIn aspires to create systems that are elegant and refined to the point of being invisible
Lot’s of open source solutions melded to achieve this orchestra of tools that provides this invisible infrastructure(that’s the cloud!).
Will they move to Azure with Microsoft acquisition is something we have to see!.