From what i understand about clusters, there is one master computer and the rest are slaves. If a slave goes down it really doesnt matter but if the master goes down the cluster is toast.
Your understanding is wrong. The idea of clusters and high-availability is that there is no single point of failure - that means that failure of one single component (be it a computer in a cluster or a hardware device inside a computer) does not prevent operation of the entire system.
So even if in your architecture there will be some "master" and "slave" roles, the slaves will be able to take over master responsibilities in case the old master goes to lunch.