Consensus

Raft, Paxos, Zab; FLP result; ZooKeeper/etcd; equivalence theorem (linearizable CAS = total order broadcast = locks = uniqueness)

Raft state machine (follower/candidate/leader); election terms; CAS+lease practical approach; fencing tokens for mutual exclusion; leader as SPOF

Link models (fair-loss/reliable/authenticated), process failure models (Byzantine/crash-recovery/crash-stop), timing models (sync/async/partial sync); default assumptions

*Understanding Distributed Systems* — Roberto Vitillo