You have configured a classic load balancer in the public subnet with EC2 instances behind them. You are sending an HTTP request using the DNS name as the destination. But you are not getting the response from the underlying instances. Which of the following checks should you carry out? Choose 2 answers from the options given below.

Answer options:

A.Ensure the load balancer is created in the public subnet.
B.Ensure the load balancer is created in the private subnet.
C.Ensure the Security group for the load balancer accepts traffic on port 80 from10.0.0.0/16.
D.Ensure the Security group for the load balancer accepts traffic on port 80 from0.0.0.0/0.

Answer – A and D
These checks are also given in the AWS Documentation.
Troubleshoot a Classic Load Balancer: Client Connectivity
If your Internet-facing load balancer in a VPC is not responding to requests, check for the following.
Your Internet-facing load balancer is attached to a private subnet
Verify that you specified public subnets for your load balancer. A public subnet has a route to the Internet Gateway for your virtual private cloud (VPC).
A security group or network ACL does not allow traffic
The security group for the load balancer and any network ACLs for the load balancer subnets must allow inbound traffic from the clients and outbound traffic to the clients on the listener ports. For more information, see Security Groups for Load Balancers in a VPC.Option B is incorrect since the load balancer needs to be created in the public subnet.
Option C is incorrect since the traffic needs to be allowed from anywhere.
For more information on troubleshooting the load balancer, one can visit the below URLs
https://docs.aws.amazon.com/elasticloadbalancing/latest/classic/ts-elb-connection-failed.html
https://docs.aws.amazon.com/elasticloadbalancing/latest/classic/elb-troubleshooting.html