DEVintermediate

Raft Consensus from Scratch: Leader Election to Log Replication

by EvaChen

Build a working Raft consensus implementation from the ground up. Covers leader election, log replication with conflict resolution, and a complete working implementation in Go. No Paxos required.

Quality Score
Quality: 65/100

Curriculum

  • Leader Election

    • Election Timers and Vote Requests
    • Handling Network Partitions During Elections

  • Log Replication

    • AppendEntries and Conflict Resolution
    • Snapshotting and Log Compaction

  • Complete Implementation

    • Putting It All Together in Go
Free PreviewLeader Election · Election Timers and Vote Requests

Leader Election in Raft

Raft separates consensus into leader election and log replication. This lesson covers the election mechanism.

How Elections Work

Every node starts as a follower. If a follower receives no heartbeat within a randomized timeout (150-300ms), it becomes a candidate and starts an election.

The Election Process

  1. Candidate increments its term
  2. Votes for itself
  3. Sends RequestVote RPCs to all other nodes
  4. Wins if it receives votes from a majority

Split Vote Prevention

Randomized election timeouts prevent most split votes. If two candidates start simultaneously, the one with the higher term wins.

Implementation Notes

The election timeout must be significantly larger than the network round-trip time. A good default is 150-300ms with heartbeats every 50ms.

Exercise

Implement the election timer and RequestVote RPC handler. Test with three nodes and verify that exactly one leader is elected.

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