5.5 Follower and candidate crashes
Until this point we have focused on leader failures. Fol- lower and candidate crashes are much simpler to han- dle than leader crashes, and they are both handled in the same way. If a follower or candidate crashes, then fu- ture RequestVote and AppendEntries RPCs sent to it will fail. Raft handles these failures by retrying indefinitely; if the crashed server restarts, then the RPC will complete successfully. If a server crashes after completing an RPC but before responding, then it will receive the same RPC again after it restarts. Raft RPCs are idempotent, so this causes no harm. For example, if a follower receives an AppendEntries request that includes log entries already present in its log, it ignores those entries in the new re- quest.
5.5 Follower 和 candidate 崩溃
到目前为止，我们只关注了 leader 崩溃的情况。Follower 和 candidate 崩溃后的处理方式比 leader 崩溃要简单的多，并且两者的处理方式是相同的。如果 follower 或者 candidate 崩溃了，那么后续发送给他们的 RequestVote 和 AppendEntries RPCs 都会失败。Raft 通过无限的重试来处理这种失败；如果崩溃的机器重启了，那么这些 RPC 就会成功地完成。如果一个服务器在完成了一个 RPC，但是还没有响应的时候崩溃了，那么在它重启之后就会再次收到同样的请求。Raft 的 RPCs 都是幂等的，所以这样的重试不会造成任何伤害。例如，一个 follower 如果收到 AppendEntries 请求但是它的日志中已经包含了这些日志条目，它就会直接忽略这个新的请求中的这些日志条目。
