Getting Started with Apache Zookeeper

Explore the four znode modes in ZooKeeper: persistent, ephemeral, sequential, and ephemeral sequential, and how they affect creation, deletion, and session-based behavior in master and worker examples.

Learn how watches and notifications replace polling by letting clients register for changes to z nodes, using one-shot watches, and receiving ordered updates for data or children.

Explore how ZooKeeper increments version numbers on data changes and uses them to guard concurrent updates, with set data and delete succeeding only when the client version matches the server.

Explore how Zookeeper architecture enables client interactions through the client library and servers. Learn how standalone and quorum modes use a Zookeeper ensemble to replicate state and serve requests.

Learn about zookeeper quorums, where the data tree is replicated across the ensemble and a majority keeps updates durable. Prefer odd server counts to tolerate crashes and avoid split-brain.

Set up a local ZooKeeper session in standalone mode, start the server, connect with the ZK CLI to localhost:2181, and create and delete a worker znode.

Explore the lifetime of a ZooKeeper session from creation to end, detailing states such as connecting, connected, and closed, and the events that trigger transitions.

Configure a three-node ZooKeeper ensemble on a single machine to form a quorum, enabling leader election and reliable coordination. Connect clients via a host:port connect string for quorum access.

Explore Zookeeper API and its Java and C bindings, clients connect to an ensemble and perform create, exists, get data, set data, get children, delete with synchronous or asynchronous methods.

Create a znode in the zookeeper ensemble using the create method with a path and data, using open ACL unsafe and persistent create mode; demonstrate with a Java example.

Explore the zookeeper getData method to retrieve data from a specified z node with a path and watcher, including one-time notifications when data changes.

Demonstrate how the zookeeper setData method updates znode data at a path using versioning, and show a java example to perform the update and verify with the zookeeper cli.

Learn how to use the Getchildren method to fetch all subnodes of a znode with a path and watcher, and print the children in a Java example.

Learn how to delete a z node in Apache Zookeeper using the delete method, checking existence and version, with a Java example that deletes the z node and its subnodes.

Set data and child watches on znodes using exist, get data, and get children, triggering events such as node created or data changed; implement a watcher to process these events.

Explore watches as a replacement for explicit cache management in zookeeper, enabling clients to cache znode data and its list of children locally while receiving asynchronous update notifications.

Explore the master worker example in Apache Zookeeper and state changes. See how mastership changes and waits for worker lists and tasks, while clients await task execution results with code.

Explore how Zookeeper recovers from recoverable failures by reestablishing sessions after disconnections, syncing connected events, and reregistering watches to maintain consistent state across clients.

Explore how the exists watch and the disconnected event affect Zookeeper session recovery; the client reestablishes watches on reconnect, but creation events can be missed in certain corner cases.

Explore leader election and fencing token, using z id to prevent external resource corruption when Zookeeper sessions fail from overload or clock drift.