An ELB automatically distributes a load/traffic across multiple instances in a part of different availability zones (AZs). The member instances can be part of single AZ or multiple AZs. An ELB becomes the single point of contact for the DNS and the end users. An ELB also monitors the instance via a health check; if the instance is healthy, then only the requests will be routed to the instance.
As we have already created instances, we will create an ELB using CLI. The command to do so is as follows:
$ aws elb create-load-balancer --load-balancer-name my-test-elb --listeners "Protocol=HTTP,LoadBalancerPort=80,InstanceProtocol=HTTP,InstancePort=80" --availability-zones us-west-2a us-west-2b
Add the newly created instance ...