AWS Classic Load Balancer

Load balancing is a very common need for any production application. In this post, I will try to demonstrate how to use a classic load balancer with AWS to manage load among various EC2 instances. I am using a simple Hello world code here which returns the address of EC2 instance, to distinguish between instances responding.

Here is the code used to return message

public class HelloWorldService
    public String helloWorld()
    	String address =" IP Address";
    	try {
		InetAddress inetAddress = InetAddress.getLocalHost();
		address = inetAddress.getHostAddress().toString();
	} catch (UnknownHostException e) {
        return "Hello World from "+ address + "!!";

After creating replicas of the same code, we have 3 instances that have now our code. Next, we need to use a load balancer that can balance out the load among these 3 instances.

Once you click on the “Create Load Balancer” button, you will be given 3 options to choose from. Application load balancer, Network load balancer, and Classic load balancer.

For the sake of this example, we will use Classic Load Balancer. First thing you will need to set the “listener port and protocol” and “target port and protocol”.

After that, you will be asked to provide more information like security groups, health check path and port, instances to be balanced, and so on. Finally, you can review and create the load balancer. Once load balance is created, you will be given a DNS name which you can use to call the service. Also, you can check instances health and set alerts if needed.

In my case, to validate that my load balancer is working, all I need to do is to hit the load balancer URL and check that the IP address returned by the call is changing, showcasing the request is going to a different server.