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 the Hazelcast cluster. For that, we will create a 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 the 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 a MultiInstanceHazelcastExample.java file (as below) which would be used for a 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 .\target\demo-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
