Zookeeper 2

Zookeeper 2 is a distributed coordination system designed for large-scale distributed applications. It helps developers to build reliable, scalable and maintainable distributed systems by providing a simple and high-performance way to manage shared resources.

Introduction

Zookeeper 2 provides a hierarchical namespace where developers can store data and watch for changes. It also provides synchronization primitives such as locks, barriers, and semaphores. This makes it easy to coordinate distributed systems and ensures that they are always in sync.

Zookeeper 2 is a master-slave architecture where there are multiple nodes acting as servers and the clients connect to them to read/write data. The servers synchronize with each other and maintain a consistent view of the system state. They handle client requests and return responses based on the current state of the system.

Features

Zookeeper 2 has the following features:

• Highly Available: Zookeeper 2 is designed to be highly available, meaning it can tolerate failures of individual nodes without affecting overall system operations.

• Reliable: Zookeeper 2 stores data redundantly across multiple servers, ensuring that data is always available even if a single node fails.

• Fast: Zookeeper 2 is designed to be fast and lightweight, with low latency for read/write operations.

• Scalable: Zookeeper 2 can handle massive amounts of data and workloads, making it suitable for large-scale applications.

Use cases

Zookeeper 2 is used in a variety of applications, including:

• Distributed Databases: Zookeeper 2 can be used to coordinate and manage distributed databases, ensuring data consistency and reliability.

• Messaging Systems: Zookeeper 2 can be used to coordinate messaging systems, ensuring that messages are delivered reliably and ordered.

• Distributed Applications: Zookeeper 2 can be used to coordinate distributed applications, providing synchronization primitives like locks and semaphores.

Getting started

To start using Zookeeper 2, you need to download and install it from the official website. Once installed, you can connect to it using the provided clients or API libraries.

Here's an example code snippet in Java using the Zookeeper API:

import org.apache.zookeeper.*;
import org.apache.zookeeper.Watcher.Event.*;
import org.apache.zookeeper.ZooDefs.*;
import java.util.concurrent.CountDownLatch;

public class ZookeeperExample implements Watcher {
    private static final String ZOOKEEPER_ADDRESS = "localhost:2181";
    private static final int SESSION_TIMEOUT_MS = 5000;
    private static final String ZNODE_PATH = "/example";

    private final CountDownLatch connectedSignal = new CountDownLatch(1);
    private ZooKeeper zooKeeper;

    public void connect() throws Exception {
        zooKeeper = new ZooKeeper(ZOOKEEPER_ADDRESS, SESSION_TIMEOUT_MS, this);
        connectedSignal.await();
    }

    public void process(WatchedEvent event) {
        if (event.getState() == KeeperState.SyncConnected) {
            connectedSignal.countDown();
        }
    }

    public void setData(String data) throws Exception {
        byte[] bytes = data.getBytes();
        zooKeeper.setData(ZNODE_PATH, bytes, -1);
    }

    public String getData() throws Exception {
        byte[] bytes = zooKeeper.getData(ZNODE_PATH, false, null);
        return new String(bytes);
    }

    public void close() throws Exception {
        zooKeeper.close();
    }

    public static void main(String[] args) throws Exception {
        ZookeeperExample example = new ZookeeperExample();
        example.connect();
        example.setData("Hello, World!");
        System.out.println(example.getData());
        example.close();
    }
}

This code connects to Zookeeper 2, sets data at a particular path, retrieves the data, and then closes the connection. It uses the asynchronous API to handle events.

Conclusion

Zookeeper 2 is an essential tool for developers building distributed systems. It provides synchronization primitives and coordination services to ensure that such systems are reliable, scalable, and maintainable. Using Zookeeper 2, developers can build distributed systems with confidence.