What is a tie-breaker, and do I need one in two-node clusters?
Tie-breakers are additional heuristics that allow a cluster partition to decide whether or not it is quorate in the event of an even-split – prior to fencing. A typical tie-breaker construct is an IP tie-breaker, sometimes called a ping node. With such a tie-breaker, nodes not only monitor each other, but also an upstream router that is on the same path as cluster communications.
