What is Raft?

Raft is a consensus algorithm designed to be easy to understand. It gives the same kind of fault tolerance as Paxos for crash failures: as long as a majority of nodes are alive, the cluster keeps working.
Raft is not a blockchain algorithm. It is used in — Kubernetes etcd, HashiCorp Consul, CockroachDB — to replicate configuration and data inside your datacenter.

How Raft works

Leader election — one node becomes Leader; others are Followers.
Log replication — client writes go to the Leader; Leader appends to its log and copies to Followers.
Commit — once a majority has stored an entry, it is committed and applied to the state machine.
Safety — if the Leader dies, a new election runs; committed entries are never lost.

sequenceDiagram
  participant Client
  participant L as Leader (C)
  participant F1 as Follower A
  participant F2 as Follower B
  participant F3 as Follower D
  participant F4 as Follower E

  Note over L,F4: 1. C wins election (3 of 5 votes)

  Client->>L: SET config/key = "prod-v2"
  L->>L: Append entry #42 to local log
  L->>F1: AppendEntries #42
  L->>F2: AppendEntries #42
  L->>F3: AppendEntries #42
  L->>F4: AppendEntries #42
  F1-->>L: OK
  F2-->>L: OK
  F3-->>L: OK
  Note over L: Majority (3/5) acked → commit #42
  L-->>Client: Success