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  13761642169

  2019-09-29

  使用raft协议的系统，只有leader可以接受写请求，follower接受读请求？

  作者回复: Etcd支持以下两种read：
  
  1. Linearizable read(默认): 需要由Leader发起，Leader发送一个请求给所有节点，在收到多数节点的响应之后，才把结果返回给客户端。如果一个follower收到linearizable read的请求，需要转发给leader来处理。
  2. Serializable read（使用Get API的话要加WithSerializable选项）: Leader和follower都可以在本地处理，时延低。
  
  只有Etcd的leader才能处理write。Follower在接到write请求后，要转发给leader来处理。
  
  参见https://github.com/etcd-io/etcd/blob/master/Documentation/faq.md#do-clients-have-to-send-requests-to-the-etcd-leader：
  > Raft is leader-based; the leader handles all client requests which need cluster consensus. However, the client does not need to know which node is the leader. Any request that requires consensus sent to a follower is automatically forwarded to the leader. Requests that do not require consensus (e.g., serialized reads) can be processed by any cluster member.

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