Check this tutorial How To Create a High Availability Setup with Corosync, Pacemaker, and Floating IPs on Ubuntu 14.04

I don’t have experience on this, but I found something you could need.

You could have use of How To Use Nginx as a Global Traffic Director on Debian or Ubuntu.

I think this is something that can help you more. You could check geo-location of user, and depends on it redirect them to server in their region. In this case, content will load faster, because server is in their region.

The negative side that users in SFO will have special subdomain, sfo.example.com, yet users in AUS and users near to AUS will have only example.com or aus.example.com.

Don’t forget, for quality content, you should have same content on both server.
I recommend you researching you about:
Configuration management. This will help you configure servers, and have same configuration on both. Personally, I would recommend Ansible, which is in my opinion easiest.
Database replication
Content replication

If you need more help, don’t hesitate to ask :)