Consensus & coordination Study Portal

Key takeaways

• Majorities overlap; 2f + 1 nodes tolerate f failures; use odd cluster sizes.
• Raft: randomised elections per term, majority-replicated log, newer term always wins.
• Use etcd, ZooKeeper or Consul rather than hand-rolling consensus; keep their data small.
• Leases expire while holders pause; fencing tokens checked by the resource are what make locks correct.
• Efficiency locks can be simple; correctness locks need consensus plus fencing.
• Split-brain is prevented by quorum plus fencing, not by timeouts alone.
• Consensus replicates one state; 2PC coordinates different participants.