Consensus / Raft
Watch leader election, log replication, and quorum as nodes join, crash, and recover.
Term
1
Leader
N0
Quorum
3
Committed
0
Leader Follower Down
Committed log
none yet
All nodes up. Quorum needs 3 of 5. With no leader, auto-append does nothing and committed entries stop growing until you Elect a new leader.
How this simulator works
One node is the leader and replicates its log to followers. An entry is committed only once a majority of the cluster holds it. Kill the leader or drop below a quorum and writes stall.
Leader election
- A candidate becomes leader only with votes from a majority of the whole cluster.
- Fewer than a majority of nodes alive → no election can succeed, so there is no leader.
- Crash the leader and the group must elect a new one before writes resume.
Quorum and commit
- Quorum = floor(N/2) + 1. With 5 nodes that is 3.
- An entry is committed once a majority of nodes have replicated it — then it is safe.
- If a minority holds the latest entry, it is NOT committed and can be overwritten.