Hazelcast can be run in isolation (single node) or multiple nodes can be run to form a cluster. Let us first try starting a single instance.

Single Instance

Example

Now, let us try creating and using a single instance of Hazelcast cluster. For that, we will create SingleInstanceHazelcastExample.java file.

package com.example.demo;

import java.util.Map;
import com.hazelcast.core.Hazelcast;
import com.hazelcast.core.HazelcastInstance;

public class SingleInstanceHazelcastExample {
   public static void main(String... args){
      //initialize hazelcast server/instance
      HazelcastInstance hazelcast = Hazelcast.newHazelcastInstance();
      System.out.println(“Hello world”);
        
      // perform a graceful shutdown
      hazelcast.shutdown();
   }
}

Now let’s compile the code and execute it −

mvn clean install
java -cp target/demo-0.0.1-SNAPSHOT.jar
com.example.demo.SingleInstanceHazelcastExample

Output

If you execute above code, the output would be −

Hello World

However, more importantly, you will also notice log lines from Hazelcast which signifies that Hazelcast has started. Since we are running this code only once, i.e., a single JVM, we would only have one member in our cluster.

Jan 30, 2021 10:26:51 AM com.hazelcast.config.XmlConfigLocator
INFO: Loading ''hazelcast-default.xml'' from classpath.
Jan 30, 2021 10:26:51 AM com.hazelcast.instance.AddressPicker
INFO: [LOCAL] [dev] [3.12.12] Prefer IPv4 stack is true.
Jan 30, 2021 10:26:52 AM com.hazelcast.instance.AddressPicker
INFO: [LOCAL] [dev] [3.12.12] Picked [localhost]:5701, using socket
ServerSocket[addr=/0:0:0:0:0:0:0:0,localport=5701], bind any local is true
Jan 30, 2021 10:26:52 AM com.hazelcast.system
...

Members {size:1, ver:1} [
   Member [localhost]:5701 - 9b764311-9f74-40e5-8a0a-85193bce227b this
]

Jan 30, 2021 10:26:56 AM com.hazelcast.core.LifecycleService
INFO: [localhost]:5701 [dev] [3.12.12] [localhost]:5701 is STARTED
...

You will also notice log lines from Hazelcast at the end which signifies
Hazelcast was shutdown:
INFO: [localhost]:5701 [dev] [3.12.12] Hazelcast Shutdown is completed in 784 ms.
Jan 30, 2021 10:26:57 AM com.hazelcast.core.LifecycleService
INFO: [localhost]:5701 [dev] [3.12.12] [localhost]:5701 is SHUTDOWN

Cluster: Multi Instance

Now, let”s create MultiInstanceHazelcastExample.java file (as below) which would be used for multi-instance cluster.

package com.example.demo;

import com.hazelcast.core.Hazelcast;
import com.hazelcast.core.HazelcastInstance;

public class MultiInstanceHazelcastExample {
   public static void main(String... args) throws InterruptedException{
      //initialize hazelcast server/instance
      HazelcastInstance hazelcast = Hazelcast.newHazelcastInstance();
        
      //print the socket address of this member and also the size of the cluster
      System.out.println(String.format("[%s]: No. of hazelcast members: %s",
         hazelcast.getCluster().getLocalMember().getSocketAddress(),
         hazelcast.getCluster().getMembers().size()));
        
      // wait for the member to join
      Thread.sleep(30000);
        
      //perform a graceful shutdown
      hazelcast.shutdown();
   }
}

Let’s execute the following command on two different shells −

java -cp .targetdemo-0.0.1-SNAPSHOT.jar
com.example.demo.MultiInstanceHazelcastExample

You would notice on the 1st shell that a Hazelcast instance has been started and a member has been assigned. Note the last line of output which says that there is a single member using port 5701.

Jan 30, 2021 12:20:21 PM com.hazelcast.internal.cluster.ClusterService
INFO: [localhost]:5701 [dev] [3.12.12]
Members {size:1, ver:1} [
   Member [localhost]:5701 - b0d5607b-47ab-47a2-b0eb-6c17c031fc2f this
]
Jan 30, 2021 12:20:21 PM com.hazelcast.core.LifecycleService
INFO: [localhost]:5701 [dev] [3.12.12] [localhost]:5701 is STARTED
[/localhost:5701]: No. of hazelcast members: 1

You would notice on the 2nd shell that a Hazelcast instance has joined the 1st instance. Note the last line of the output which says that there are now two members using port 5702.

INFO: [localhost]:5702 [dev] [3.12.12]
Members {size:2, ver:2} [
   Member [localhost]:5701 - b0d5607b-47ab-47a2-b0eb-6c17c031fc2f
   Member [localhost]:5702 - 037b5fd9-1a1e-46f2-ae59-14c7b9724ec6 this
]
Jan 30, 2021 12:20:46 PM com.hazelcast.core.LifecycleService
INFO: [localhost]:5702 [dev] [3.12.12] [localhost]:5702 is STARTED
[/localhost:5702]: No. of hazelcast members: 2