While deceptively simple, there's actually a lot of thought involved in correctly placing an odd node, and why we use witness nodes rather than yet another PostgreSQL replica:
- Our first guideline is the most straightforward of these, such that we ensure there are an odd number of nodes in the cluster. Once we have that, any event in the cluster is submitted to the entire quorum for a decision, and only agreement guarantees subsequent action. Further, since the witness cannot vote for itself, only one eligible node will ever win the election. Consider this sample cluster diagram:
We have three nodes in this cluster and, in ...
