Do not know where to start for server redundancy
I do not know which direction to take but here is my problem:
We have 2 servers which basically run identical software and automatically assign them selfs as master or standby or alone based on the condition of the other server. The problem is they both have 2 IP address, and one would have to manually go to the other address to access the web interface when the condition of the servers change. What would be required to have a single (i guess virtual IP) that routes to the master or standalone server at all times? Can i use pfsense to do this combined with some software that is put on the 2 servers?
This sounds more like a job for Linux Heartbeat than for Pfsense. From what you wrote it sounds like you have intelligence at the server level to determine which should be master and which should be slave. Linux Heartbeat does a very good job at shifting around virtual IPs and services…
If you wanted to use Pfsense, you could set up a failover load balance pool. The only problem there is that you would have to kill the primary server if you wanted failover to occur.