Apache Zookeeper Explained: Tutorial, Use Cases and Zookeeper Java API Examples
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This document provides an overview of Apache Zookeeper, a distributed coordination service. It discusses Zookeeper's data model, use of ZAB protocol for consensus, and common use cases such as naming, configuration management, and leader election. It also provides a brief Java client API example.
Apache Zookeeper Explained: Tutorial, Use Cases and Zookeeper Java API Examples
- 2. Agenda Coordination headache in distributed applications What is zookeeper? Zookeeper Overview Zookeeper Service & Data Model ZAB (Zookeeper Atomic Broadcasting Protocol) Zookeeper Read, Write and Watch Zookeeper Use Cases Zookeeper Client API Example
- 3. Coordination headache in distributed applications Problem of Detection Cluster Size Estimation Leader Election Group Membership Configuration Management Consensus among multiple parties is difficult in dynamic distributed systems as members may leave/fail/join anytime Consistency, Availability and Partition tolerance
- 4. What is Zookeeper? Apache Zookeeper is a highly consistent, scalable and reliable cluster co-ordination service. Zookeeper is a CP system where Consistency and Partition tolerance are guaranteed. Off-the-shelf support for implementing consensus, group management, leader election etc. Zookeeper cluster is called Ensemble Ensemble has one leader and remaining followers Zookeeper is a Distributed Coordination Service for Distributed Applications. Zookeeper is originally developed by Yahoo research Team and became a top level Apache project. Zookeeper is used by many enterprises including Rackspace, Yahoo! and eBay.
- 5. Zookeeper Overview Zookeeper use Zookeeper Broadcasting Protocol (ZAB) for ordering and integrity. Achieves High availability and performance via replication. Low latency and high throughput via in memory image of data tree ,transaction logs and snapshots. Uses “quorum” model and will only be available if a majority of servers are alive (by a strict majority of nodes). Zookeeper relies on a quorum for durability as well. Pipelined architecture of Zookeeper enables the execution of operations from a single client in FIFO order. Ordered updates uses ZAB protocol (a leader-based atomic broadcast protocol) for Ordering, Integrity , exactly once. Election of a new leader is followed by a synchronization phase before any new changes are accepted.
- 6. Zookeeper Service & Data Model At any given time, one Zookeeper client is connected to one Zookeeper server. If the node (to which client connected) fails, client automatically connect to another server in ensemble with transparent session transfer. Znode is an in-memory data node in Zookeeper Data organized in a hierarchical namespace (data tree) The data model of ZooKeeper (znode) is essentially a file system with a simplified API and associated meta data and versions. Regular, Ephemeral and Sequential Znode are supported. Each ZNode is using UNIX style notation. For example, /A/B/C to denote the path to znode C, where C has B as its parent and B has A as its parent. All znodes store data, and all znodes, except for ephemeral znodes, can have children.
- 7. Zookeeper read/write/watch Clients make use of Zookeeper API to update/write Zookeeper the data tree. All Updates are ordered and managed by leader with unique zxid and are considered complete when a quorum confirms the update. The leader executes update request and broadcasts the change to the ZooKeeper state through Zab. Zab by default uses a simple majority quorums to decide on a proposal. Read and Watch requests on the znode sent by a client to a ZooKeeper server are processed locally. Watch –Allows client to get notification if an already returned information gets updated.
- 9. Zookeeper read/write/watch Read and Watch requests on the znode are processed locally but, write requests are propagated to leader server and go through a consensus before a response is generated. Throughput of read request increases with number of servers and throughput of write requests, decreases with number of servers.
- 10. Zookeeper use cases ZooKeeper offers the library to create and manage synchronization primitives. ZooKeeper avoids the single-point-of-failure. Typical use cases , Naming service Configuration management Synchronization Leader election Message Queue Notification system
- 11. Zookeeper Java Client API Examples A simple example. To check the complete example see at the below link. http://java.globinch.com/enterprise- services/zookeeper/apache-zookeeper-explained- tutorial-cases-zookeeper-java-api-examples/
Editor's Notes
- #4: 1)Number of non-faulty nodes currently in the system (heartbeat.Distributed Hashtables (DHT)) Leader/master detection & availability Membership notifications etc. 2)