setup second domain controller as backup

hello,

need help, i started a project at work setting up a second dc on our domain. I am done with the setup part now i need to dc#2 to be a backup so incase dc#1 ever goes out dc#2 will now takeover as the main dc. dc#1 gets backed up every night so i also need to be able to point that backup folder to dc#2 so it too has the backup as well. Im using server 2012 r2 by the way if that helps any.

thanks,