write TransientWorker class

worker/src/main/java/worker/TransientWorker.java

+package worker;
+
+import org.apache.zookeeper.*;
+import common.ZkConfig;
+import java.io.IOException;
+import java.util.Random;
+import java.util.concurrent.locks.LockSupport;
+
+public class TransientWorker {
+
+    private static final float CHANCE_TO_FAIL = 0.1F;
+    private final Random random = new Random();
+    private ZooKeeper zooKeeper;
+    private final String nodeId;
+
+    public TransientWorker(String nodeId) {
+        this.nodeId = nodeId;
+    }
+
+    public static void main(String[] args) {
+        if (args.length < 1) {
+            System.out.println("Usage: java -jar TransientWorker.jar <nodeId>");
+            System.exit(1);
+        }
+
+        String nodeId = args[0];
+        TransientWorker worker = new TransientWorker(nodeId);
+
+        try {
+            worker.connectToZookeeper();
+            worker.work();
+        } catch (Exception e) {
+            System.err.println("Worker on node [" + nodeId + "] crashed: " + e.getMessage());
+            System.exit(1);
+        }
+    }
+
+    public void connectToZookeeper() throws IOException {
+        // We can pass null for the watcher since the worker doesn't need to respond to events
+        this.zooKeeper = new ZooKeeper(ZkConfig.ZOOKEEPER_ADDRESS, ZkConfig.SESSION_TIMEOUT, null);
+    }
+
+    public void work() throws KeeperException, InterruptedException {
+        registerWorkerInCluster();
+
+        while (true) {
+            System.out.println("Worker on node [" + nodeId + "] is performing calculations...");
+            LockSupport.parkNanos(2_000_000_000L); // 2 seconds
+
+            if (random.nextFloat() < CHANCE_TO_FAIL) {
+                System.out.println("Critical error simulated.");
+                throw new RuntimeException("Oops! Worker crashed.");
+            }
+        }
+    }
+
+    private void registerWorkerInCluster() throws KeeperException, InterruptedException {
+        String path = ZkConfig.WORKERS_PARENT_PATH + "/worker_";
+        byte[] data = nodeId.getBytes();
+
+        // Create ephemeral sequential node to signal presence
+        zooKeeper.create(path, data, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
+    }
+}
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