Added final README.md

README.md

+
+
+
+
+
+#  What Is the Herd Effect?
+(This defination is taked from google)
+
+In a naive leader election system:
+
+1. When a leader fails or disconnects,
+2. ZooKeeper sends a notification to all nodes,
+3. All nodes simultaneously try to become the next leader,
+4. This results in a massive spike of requests hitting ZooKeeper at once.
+
+This creates:
+
+- High CPU usage  
+- High network load  
+- Performance degradation as the cluster grows  
+
+This is known as the Herd Effect.
+
+---
+
+# How This small demo Solution Avoids the Herd Effect
+
+I used **Ephemeral Sequential znodes**, a built-in ZooKeeper pattern for safe and efficient leader election.
+
+### How it works:
+
+1. Each node creates an **ephemeral sequential** znode under:
+```
+
+/election/node_
+
+```
+
+2. ZooKeeper automatically assigns each client a unique number:
+```
+
+node_0000001
+node_0000002
+node_0000003
+
+```
+
+3. The node with the smallest number is the leader.
+
+4. Non-leader nodes do NOT watch the leader.  
+Instead, each node watches **only the node directly before it** (its predecessor).
+
+### Why this avoids the Herd Effect:
+
+- Only one node wakes up when a failure happens  
+- Only the node whose predecessor disappeared runs an election step  
+- Zero thundering herd  
+- ZooKeeper load stays small, even with hundreds or thousands of clients
+
+This is the most scalable and recommended approach for leader election with ZooKeeper.
+
+---
+
+#  Project Structure
+
+```
+
+src/main/java/com/ds/LeaderElection/
+│── App.java
+│── LeaderElection.java
+│── ZKConnection.java
+launch.sh              (starts ZooKeeper ensemble)
+pom.xml
+README.md
+conf/  --> contains configuration for launch.sh
+````
+
+---
+
+#  Running the Project
+
+### 1. Start ZooKeeper Ensemble
+
+The project includes a `launch.sh` script that starts 3 ZooKeeper servers
+defined in The configuration files.
+
+Run:
+
+```bash
+./launch.sh
+````
+
+This boots ZooKeeper servers on ports:
+
+* 2181
+* 2182
+* 2183
+
+With corresponding quorum and election ports.
+
+---
+
+### 2. Run the leader election demo
+
+Open multiple terminals, and from the project root, run:
+
+```bash
+mvn exec:java
+```
+
+Run it 2x, 3x, or more times to simulate multiple clients.
+
+Each instance will:
+
+* Connect to ZooKeeper
+* Create an ephemeral sequential node
+* Either become the leader
+* Or watch its predecessor
+* Automatically take over leadership when needed
+
+
+
+
+
+
+
+
+
+```