I'm no expert, but I think the main idea is to have an odd number of nodes plus a consensus protocol like Paxos or Raft to figure out who's actually alive. If a

I'm no expert, but I think the main idea is to have an odd number of nodes plus a consensus protocol like Paxos or Raft to figure out who's actually alive. If a node finds itself in a split minority, it won't become a master. This doesn't work when you have only two nodes, as there's no minority after the split, both sides are equal. Building this from scratch is extremely difficult and error-prone, so people usually use systems like ZooKeeper.