The big site like Google, Facebook and co test their new features on a particular group of people. I wondered how he did that : both in programmation and architecture (cache ...).
--Edit-- Server side, if I several version of one function How do you do to first version of this function run on 90% of the people, the version 2 of this function to 5% and the version to 5% remaining.
Or to be most simple, if I have a version of my site operational, and 2 versions modified of site. How do ou run the three instance of site for differents persons. -- !Edit --
What Do Symfony do it ? or other framework (spring, django) ?