Raft: Understandable Distributed Consensus
Master the Raft consensus algorithm: Leader election, heartbeat heartbeats, log replication, commit index, and election safety.
01.1. Why Raft Replaced Paxos in Modern Distributed Systems
Despite Paxos being mathematically rigorous, it was widely criticized in the distributed systems community for being notoriously difficult to comprehend and implement in production software.
In 2014, Diego Ongaro and John Ousterhout at Stanford University introduced Raft, designed with a primary objective: Understandability. Raft delivers equivalent formal safety and performance guarantees to Multi-Paxos while decomposing consensus into three independent, modular sub-problems:
- Leader Election: Electing a single authoritative leader when the existing leader crashes or disconnects.
- Log Replication: The leader accepts log entries from clients, appends them locally, and forces followers to synchronize their logs.
- Safety (State Machine Invariant): If any server has applied an entry at a given index to its state machine, no other server will ever apply a different entry for that same index.
Raft 3-State Machine Lifecycle 🔄
Raft 3-State Machine Lifecycle 🔄
Transitions between Follower, Candidate, and Leader states.
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