Server 2012 w./ 4 vm's running. How to put in place a setup secondary server as a "standby" or backup server.

I am running Windows Server 2012 with 4 Hyper V VM's.  If this server fails, I want to have in a place a secondary server that I can manually activate.  How can I set this up with the existing Hyper V info and not have to start over. The new (secondary) server will be 2012R2.  I can NOT redo the hard drives but want to configure the secondary server to take over if primary fails.  Is clustering an option??  How can I do this with the least amount of hassle??