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Leader_Election
Commit 86f4dfc1 authored by areej.mohammad's avatar areej.mohammad
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<component name="VcsDirectoryMappings">
<mapping directory="$PROJECT_DIR$" vcs="Git" />
</component>
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pom.xml 0 → 100644
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<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>org.example</groupId>
<artifactId>zookeeper_client</artifactId>
<version>1.0-SNAPSHOT</version>
<properties>
<maven.compiler.source>17</maven.compiler.source>
<maven.compiler.target>17</maven.compiler.target>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<dependencies>
<dependency>
<groupId>org.apache.zookeeper</groupId>
<artifactId>zookeeper</artifactId>
<version>3.8.5</version> <exclusions>
<exclusion>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
</exclusion>
</exclusions>
</dependency>
</dependencies>
</project>
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src/main/java/org/example/LeaderElection.java 0 → 100644
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package org.example;
import org.apache.zookeeper.*;
import org.apache.zookeeper.data.Stat;
import java.io.IOException;
import java.util.Collections;
import java.util.List;
public class LeaderElection implements Watcher {
private static final String address = "192.168.144.134:2181";
private static final int SESSION_TIMEOUT = 3000; //dead client
private static final String ELECTION_NAMESPACE = "/election";
private String currentZnodeName;
private ZooKeeper zooKeeper;
public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
LeaderElection leaderElection = new LeaderElection();
leaderElection.connectToZookeeper();
leaderElection.volunteerForLeadership();
leaderElection.electLeader();
leaderElection.run();
leaderElection.close();
System.out.println("Successfully Closed");
}
public void volunteerForLeadership() throws InterruptedException, KeeperException {
String znodePrefix = ELECTION_NAMESPACE + "/c_";
String znodeFullPath = zooKeeper.create(znodePrefix, new byte[]{}, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
System.out.println(znodeFullPath);
this.currentZnodeName = znodeFullPath.replace(ELECTION_NAMESPACE + "/", "");
}
public void electLeader() throws InterruptedException, KeeperException {
List<String> children = zooKeeper.getChildren(ELECTION_NAMESPACE, this);
Collections.sort(children);
String smallestChild = children.get(0); //the first element
if (smallestChild.equals(currentZnodeName)) {
System.out.println("I'm a leader");
} else {
System.out.println("I'm not a leader" + smallestChild + " is a leader.");
}
}
private void close() throws InterruptedException {
this.zooKeeper.close();
}
public void connectToZookeeper() throws IOException {
this.zooKeeper = new ZooKeeper(address, SESSION_TIMEOUT, this);
}
public void run() throws InterruptedException {
synchronized (zooKeeper) {
zooKeeper.wait();
}
}
@Override
public void process(WatchedEvent watchedEvent) {
switch (watchedEvent.getType()) {
case None:
if (watchedEvent.getState() == Event.KeeperState.SyncConnected) {
System.out.println("Successfully connected to Zookeeper");
} else if (watchedEvent.getState() == Event.KeeperState.Disconnected) {
synchronized (zooKeeper) {
System.out.println("Disconnected from Zookeeper");
zooKeeper.notifyAll();
}
} else if (watchedEvent.getState() == Event.KeeperState.Closed) {
System.out.println("Closed Successfully");
}
case NodeChildrenChanged:
try {
electLeader();
System.out.println(ELECTION_NAMESPACE + " NodeChildrenChanged");
} catch (InterruptedException e) {
throw new RuntimeException(e);
} catch (KeeperException e) {
throw new RuntimeException(e);
}
}
}
}
src/main/java/org/example/LeaderElectionImprovement.java 0 → 100644
View file @ 86f4dfc1
package org.example;
import org.apache.zookeeper.*;
import org.apache.zookeeper.data.Stat;
import java.io.IOException;
import java.util.Collections;
import java.util.List;
public class LeaderElectionImprovement implements Watcher {
// **1. Connection Settings**
private static final String address = "192.168.144.134:2181";
private static final int SESSION_TIMEOUT = 3000;
private static final String ELECTION_NAMESPACE = "/election";
private String currentZnodeName;
private ZooKeeper zooKeeper;
public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
// Class Instance
LeaderElectionImprovement leaderElectionImprovement = new LeaderElectionImprovement();
leaderElectionImprovement.connectToZookeeper();
leaderElectionImprovement.volunteerForLeadership();
leaderElectionImprovement.electLeader();
leaderElectionImprovement.run();
leaderElectionImprovement.close();
System.out.println("Successfully Closed");
}
public void volunteerForLeadership() throws InterruptedException, KeeperException {
String znodePrefix = ELECTION_NAMESPACE + "/c_";
// Creating an Ephemeral Sequential znode
String znodeFullPath = zooKeeper.create(znodePrefix, new byte[]{}, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
System.out.println(" Successfully volunteered. Full Znode path: " + znodeFullPath);
this.currentZnodeName = znodeFullPath.replace(ELECTION_NAMESPACE + "/", "");
}
public void electLeader() throws InterruptedException, KeeperException {
// Getting children without setting a watcher on the parent node (false)
List<String> children = zooKeeper.getChildren(ELECTION_NAMESPACE, false);
Collections.sort(children); // Sorting the children
String smallestChild = children.get(0);
int index = children.indexOf(currentZnodeName);
if (index == 0) {
// I am the Leader!
System.out.println(" I am the Leader!");
} else {
// I am a Follower. I must watch the immediately preceding rival.
String smallerZnodeName = children.get(index - 1);
String watcherZnodePath = ELECTION_NAMESPACE + "/" + smallerZnodeName;
System.out.println(" I am a Follower.");
System.out.println(" I will watch the closest preceding rival: " + smallerZnodeName);
// Using exists() to set a NodeDeleted Watcher on the preceding node only
Stat stat = zooKeeper.exists(watcherZnodePath, this);
if (stat == null) {
// If the previous znode is not found, it means it was deleted before we set the watcher.
System.out.println(" Failure! Preceding znode already deleted. Re-electing immediately.");
electLeader();
}
}
}
private void close() throws InterruptedException {
this.zooKeeper.close();
}
public void connectToZookeeper() throws IOException {
this.zooKeeper = new ZooKeeper(address, SESSION_TIMEOUT, this);
}
public void run() throws InterruptedException {
// Keeps the main thread waiting to process Watcher events
synchronized (zooKeeper) {
zooKeeper.wait();
}
}
@Override
public void process(WatchedEvent watchedEvent) {
// Connection and Disconnection handling
if (watchedEvent.getType() == Event.EventType.None) {
if (watchedEvent.getState() == Event.KeeperState.SyncConnected) {
System.out.println(" Successfully connected to Zookeeper");
} else if (watchedEvent.getState() == Event.KeeperState.Disconnected) {
synchronized (zooKeeper) {
System.out.println(" Disconnected from Zookeeper");
zooKeeper.notifyAll();
}
}
}
// **Handling the Deletion Event**
if (watchedEvent.getType() == Event.EventType.NodeDeleted) {
// This is triggered when the znode we are watching (our preceding rival) is deleted
try {
System.out.println(" Notification! Rival we were watching has been deleted: " + watchedEvent.getPath());
electLeader(); // Re-elect to determine if we are the new leader
} catch (InterruptedException | KeeperException e) {
e.printStackTrace();
}
}
}
}
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src/main/java/org/example/WatchersAndTriggers.java 0 → 100644
View file @ 86f4dfc1
package org.example;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.data.Stat;
import java.io.IOException;
import java.util.List;
import java.io.IOException;
//import org.apache.zookeeper.ZooKeeper;
public class WatchersAndTriggers implements Watcher {
private static final String address="192.168.144.134:2181";
private static final int SESSION_TIMEOUT = 3000; //dead client
private static final String TargetZnode = "/target_znode";
static ZooKeeper zooKeeper;
public static void main(String[] args) throws IOException ,InterruptedException , KeeperException {
WatchersAndTriggers watchersAndTriggers = new WatchersAndTriggers();
watchersAndTriggers.connectToZookeeper();
watchersAndTriggers.testWatcher();
watchersAndTriggers.run();
watchersAndTriggers.close();
}
private void close() throws InterruptedException {
this.zooKeeper.close();
}
private void run() throws InterruptedException {
synchronized (zooKeeper) {
this.zooKeeper.wait();
}
}
private void connectToZookeeper() throws IOException {
this.zooKeeper = new ZooKeeper(address, SESSION_TIMEOUT, this);
}
public void testWatcher() throws InterruptedException, KeeperException {
Stat stat = zooKeeper.exists(TargetZnode, this);
if (stat == null) {
System.out.println(TargetZnode + " not exist");
return;
}
byte[] data = zooKeeper.getData(TargetZnode, this, stat);
List<String> children = zooKeeper.getChildren(TargetZnode, this);
System.out.println("Data " + new String(data) + "children " + children);
}
@Override
public void process(WatchedEvent watchedEvent) {
switch (watchedEvent.getType()) {
case None:
if (watchedEvent.getState() == Event.KeeperState.SyncConnected) {
System.out.println("Successfully connected to Zookeeper");
} else if (watchedEvent.getState() == Event.KeeperState.Disconnected) {
synchronized (zooKeeper) {
System.out.println("Disconnected from Zookeeper");
zooKeeper.notifyAll();
}
} else if (watchedEvent.getState() == Event.KeeperState.Closed) {
System.out.println("Closed Successfully");
}
case NodeCreated:
System.out.println(TargetZnode + " Created");
break;
case NodeDeleted:
System.out.println(TargetZnode + " Deleted");
break;
case NodeDataChanged:
System.out.println(TargetZnode + " DataChanged");
break;
case NodeChildrenChanged:
System.out.println(TargetZnode + " ChildrenChanged");
break;
}
try {
testWatcher();
} catch (InterruptedException e) {
throw new RuntimeException(e);
} catch (KeeperException e) {
throw new RuntimeException(e);
}
}
}
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