Propagating web configuration changes to multiple servers

I have a requirement that I need to store the configuration for my website. This website will be hosted on around 100 web servers. I want to plan for a mechanism through which I can propagate the configuration changes seamlessly so as to have minimum impact on the App running onto my server.

I need to ignore the scenario of taking few servers down, updating them (while other servers are up) and follow the same process for other servers.