What is the election algorithm used by ZooKeeper?

The election algorithm used by ZooKeeper is based on the Paxos protocol called Zab (ZooKeeper Atomic Broadcast) protocol. In this protocol, all nodes in the ZooKeeper cluster will go through a leader election process to choose one node as the “leader” responsible for handling client requests and maintaining consistency among the nodes in the cluster.

In short, the election algorithm of ZooKeeper follows the following steps:

1. Initial stage: All nodes are in the LOOKING state, attempting to gain leadership status.
2. Voting with your ballot: Nodes will vote with each other and decide which node to vote for based on the rules.
3. Vote counting: each node will collect voting results and determine the final leader based on the majority of nodes’ votes.
4. Leadership election: the selected node ultimately becomes the leader, while the other nodes become followers or observers.

This election algorithm ensures that only one leader exists in the ZooKeeper cluster, preventing data inconsistency and conflict issues, while also providing high availability and reliability.