Will the servers be in the same physical location?
Yes, they are in the same location on a rack (have a private LAN between them in case they are needed).
What type of cluster are you looking to do? There are several types.
Well.. right now I have a single PGSQL Server, and if system fails, ram or power supply fails I need to have a solution to have all online until the server is repaired.
I think about mounting 2 PGSQL Servers with the same content on each, same users, permissions, etc, and both servers must write and read databases, queries from the web server must be balanced between this two servers and in case one fails, the other must have the hability to recieve all the traffic until the 1st server is online again.
I don't know if this can be done, don't have too much experience with SQL balancing, have worked with Apache balancing but this is very different, I think it will be the best solution.