Leadership transfer

Node::transfer_leadership_to(peer) asks the current leader to hand leadership to peer. Uses:

• Graceful shutdown of the current leader.
• Pinning the leader to a specific node (e.g. for locality).
• Maintenance windows.

#![allow(unused)]
fn main() {
node.transfer_leadership_to(nid(2)).await?;
}

Protocol

The leader replicates to peer until matchIndex[peer] == last_log_index, then sends TimeoutNow. The target immediately starts an election at current_term + 1. Followers with a known leader redirect; leaderless followers and candidates drop.

The call returns once the local driver has accepted the request and dispatched the engine actions. It does not wait for the new leader to be elected. The cluster may briefly have no leader if the target fails to win.

Errors

• NotLeader { leader_hint } — we are a follower.
• NoLeader — no leader currently known.
• InvalidTarget { target } — target is self or not a member of the current peer set.