Leader Election & Consensus (Raft, Paxos)

Leader election is how a distributed cluster picks one node to be in charge so the others can stop arguing. This lesson covers the consensus problem (FLP impossibility), Paxos in concept, Raft in detail (leader election + log replication + safety), the role of quorum, and the operational pitfalls of split brain and network partitions. We also tour the systems that ship Raft or Paxos in production: etcd, ZooKeeper, Consul, CockroachDB, MongoDB, Spanner. By the end you can explain why every modern distributed database has a consensus protocol at its core, and you can sketch Raft on a whiteboard.