Zookeeper 简明教程

Zookeeper - Leader Election

让我们分析一下如何在 ZooKeeper 协同程序中选举一个领导者节点。考虑集群中存在 N 节点。领导者选举过程如下 −

Let us analyze how a leader node can be elected in a ZooKeeper ensemble. Consider there are N number of nodes in a cluster. The process of leader election is as follows −

  1. All the nodes create a sequential, ephemeral znode with the same path, /app/leader_election/guid_.

  2. ZooKeeper ensemble will append the 10-digit sequence number to the path and the znode created will be /app/leader_election/guid_0000000001, /app/leader_election/guid_0000000002, etc.

  3. For a given instance, the node which creates the smallest number in the znode becomes the leader and all the other nodes are followers.

  4. Each follower node watches the znode having the next smallest number. For example, the node which creates znode /app/leader_election/guid_0000000008 will watch the znode /app/leader_election/guid_0000000007 and the node which creates the znode /app/leader_election/guid_0000000007 will watch the znode /app/leader_election/guid_0000000006.

  5. If the leader goes down, then its corresponding znode /app/leader_electionN gets deleted.

  6. The next in line follower node will get the notification through watcher about the leader removal.

  7. The next in line follower node will check if there are other znodes with the smallest number. If none, then it will assume the role of the leader. Otherwise, it finds the node which created the znode with the smallest number as leader.

  8. Similarly, all other follower nodes elect the node which created the znode with the smallest number as leader.

当从头开始时，领导选举是复杂的过程。但 ZooKeeper 服务使其非常简单。让我们在下一章转到用于开发目的的 ZooKeeper 安装。

Leader election is a complex process when it is done from scratch. But ZooKeeper service makes it very simple. Let us move on to the installation of ZooKeeper for development purpose in the next chapter.