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This article introduces the relevant knowledge of "zookeeper application implementation process". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Implement a distributed lock

The distributed lock is realized by creating a temporary sequence node under a path node of zookeeper, that is, before each thread (a thread across processes) acquires the same lock, a node needs to be created under the same path, and the node name is composed of uuid + incremental sequence. By comparing whether the sequence number is in the first place of all the child nodes, we can judge whether the lock has been acquired successfully. When it fails to acquire the lock, it adds a watcher to listen for changes in the previous node, and then waits for the state. Until the watcher event takes effect, it wakes itself up, or the timeout exception returns.

Let's analyze how to elect a leader node in the ZooKeeper collection. Consider that there are N nodes in a cluster.

The process of the leader election is as follows:

All nodes create sequential, temporary nodes with the same path / app/leader_election/guid_.

The ZooKeeper collection will append a 10-bit sequence number to the path, and the znode created will be / app/leader_election/guid_0000000001,/app/leader_election/guid_0000000002, and so on.

For a given instance, the node that creates the lowest number in znode becomes leader, while all other nodes are follower.

Each follower node monitors the next znode with the lowest number. For example, the node that created the znode/app/leader_election/guid_0000000008 monitors the znode/app/leader_election/guid_0000000007, and the node that creates the znode/app/leader_election/guid_0000000007 monitors the znode/app/leader_election/guid_0000000006.

If leader is closed, its corresponding znode/app/leader_electionN is deleted.

The next online follower node will be notified of leader removal through the monitor.

The next online follower node will check for the existence of other znode with the lowest number. If not, it will assume the role of leader. Otherwise, the node it finds to create the znode with the lowest number will be used as the leader.

Similarly, all other follower nodes elect the node that creates the znode with the lowest number as the leader.

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