Reject actions that are disruptive to the leader during configuration changes

[kuujo]

There is some potential for leaders to be disrupted during configuration changes. Since the leader updates its configuration when it logs the configuration change, servers that are removed from the leader's configuration may timeout and attempt an election. By incrementing the term and requesting a vote from the leader, a server that was removed from the leader's configuration can force the leader to step down.

§4.3.2

Handling this case requires a simple extension to the handling of VoteRequest to reject requests if received within an election timeout of receiving a heartbeat from the leader.

[kuujo]

Actually, this logic can be added to handling of PollRequest to prevent potential candidates from ever transitioning and incrementing their term in the first place. This feels much more elegant in my mind as it doesn't break the nature and spirit of monotonically increasing terms (even if the server was removed from the configuration anyways).