On the EC2 dashboard, select the Load Balancers service from the navigation pane on left.

Launch the Create Load Balancer wizard. AWS offers four types of load balancers:
Application load balancer
Network load balancer
Gateway load balancer
Classic Load BalancerInfo

A simple use case: Assume you are running a microservices-architecture based application. An Application Load Balancer allows you to host the different API endpoints of your application on different servers. The load balancer then redirects the incoming HTTP/HTTP traffic to the suitable server based on the rules you specify in the configuration.

A Network Load Balancer helps to balance the load on each individual server. Having an NLB becomes essential when your application requires handling millions of requests per second securely while maintaining ultra-low latencies.

Choose a Gateway Load Balancer when you need to deploy and manage a fleet of third-party virtual appliances that support GENEVE. These appliances enable you to improve security, compliance, and policy controls.

Choose a Classic Load Balancer when you have an existing application running in the EC2-Classic network.

Let's create a network load balancer (NLB), and see the role of a NLB.

An NLB serves as the single point of contact for clients and automatically distributes the incoming traffic uniformly across multiple targets. The targets are the EC2 instances within the same or different AZs.

An AWS account
A default VPC
Subnets in each AZ in the default VPC. Also, notice that a common route table is attached to all subnets.
A route table with a rule for internet facing communication. See that it requires an internet gateway
Target groups

Go to the EC2 dashboard. In order to use elastic load balancing, you will need to make sure that you've launched the EC2 instances that you plan to register with your load balancer.

You must have more than one EC2 instance in the running state. In the example snapshot below, we have two instances, in two different availability zones (AZs).

The steps below show how to create the first EC2 instance in a public subnet in any one Availability Zone, and install the Apache webserver on it. Auto-assign Public IP: Enable

Let's add advanced details.
Under the Advanced Details → User data section, add the following configuration script to run automatically during launch.

#!/bin/bash
sudo yum update -y
sudo amazon-linux-extras install -y lamp-mariadb10.2-php7.2 php7.2
sudo yum install -y httpd mariadb-server
sudo systemctl start httpd
sudo systemctl enable httpd
sudo chkconfig httpd on

#Set file permissions for the Apache web server
sudo groupadd www
sudo usermod -a -G www ec2-user
sudo chgrp -R www /var/www
sudo chmod 2775 /var/www
find /var/www -type d -exec sudo chmod 2775 {} +
find /var/www -type f -exec sudo chmod 0664 {} +

#Create a new PHP file at /var/www/html/ path
echo "" > /var/www/html/phpinfo.php

The script above will install, configure, and launch the Apache webserver on the EC2 instance.

Specify the user data to configure the EC2 instance

Keep the storage as default, and use a tag as Name: Server1

Go to VPC, click security group and Configure Security Group, you can create a new one, and ensure to have a firewall rule to allow incoming HTTP traffic on port 80.

Launch the second EC2 instance using the same steps above, except for the following changes at the Configure Instance Details step:

Select another public subnet in a different AZ, say us-east-2b

#!/bin/bash
sudo yum update -y
sudo amazon-linux-extras install -y lamp-mariadb10.2-php7.2 php7.2
sudo yum install -y httpd mariadb-server
sudo systemctl start httpd
sudo systemctl enable httpd
sudo chkconfig httpd on

#Set file permissions for the Apache web server
sudo groupadd www
sudo usermod -a -G www ec2-user
sudo chgrp -R www /var/www
sudo chmod 2775 /var/www
find /var/www -type d -exec sudo chmod 2775 {} +
find /var/www -type f -exec sudo chmod 0664 {} +

#Create a new PHP file at /var/www/html/ path
echo "Welcome to server 2" ?>" > /var/www/html/phpinfo.php

Additionally, change the tag to Name: Server2.

Confirm that the newly created EC2 instances are in the running state and status check is showing2/2 checks passed.
Verify that the Apache server is running successfully on both the EC2 instances. Simply copy, and paste the public IPv4 address of each instance in a new browser window. If the Apache is configured successfully, you will see the Apache welcome page.

http://54.226.12.70
http://52.202.155.208

Note: We have opened the HTTP traffic on the default port, therefore the public IPv4 address should be prepended with http://, instead of https://.

View the content of the PHP page that you configured using the shell script.

http://54.226.12.70/phpinfo.php
http://52.202.155.208/phpinfo.php

Select the Load Balancers service on the left-hand side menu of the EC2 dashboard, and click on the Create Load Balancer button.

At the Register Targets step, add the two EC2 instances created previously to the target group.

You will be taken back to the Load Balancers dashboard. Copy the DNS name of the newly created NLB, and append the /phpinfo.php at the end of it. A sample DNS name appended with the file name looks like this:
http://network-load-balancer-9ffad67548f8c722.elb.us-east-1.amazonaws.com/phpinfo.php

Paste the copied DNS name to a new browser window and refresh the browser a few times, each after a few seconds. You will notice that sometimes the request is redirected to Server-A and other times, it is routed to Server-B.

Delete the NLB by going to the Load Balancer dashboard.
Stop and terminate the EC2 instances by going to the Instances dashboard.
Delete the Target groups by going to the Target groups dashboard