Ubuntu Servers :: Create Script To Keep Machine Cluster Synced Properly Until Failover

I've been reading up on clustering a bit and want to create simple 2 machine cluster of which the 2nd one will turn on and take over traffic at the previous machine's IP (I'm aware there will be a couple minutes of downtime while the failover server boots). I've looked into doing a simple DNS round robin, but I think both machines would need to be online all the time for this to function correctly. I've also looked into linux-HA and GlusterFS but both seem a little intense for the simple failover I'm trying to achieve. One catch if approaching with DNS round robin... the server that I want to setup with a failover also operates as a DNS server. Anyone know the simplest way to complete this? One idea I had (that seemed like a bit of manual work): Create script that runs every 60 secs through CRON on firewall (running pfsense) and have it check if master-server is up. If it's not, it will send a WOL signal to the slave, which has a mirrored image of the first. the problem I have with that is I will also need to create a script to keep both synced properly which seems almost impossible if one is shut down until failover (my thought was periodic rsyncs.) Perhaps creating a FS to direct all files to for the master/slave would be the only way around that.