Securing Communication between Client and EC2 Instances Behind ELB

Answer - D.

Since there are applications that work on legacy protocols, you need to ensure that the ELB can be used at the network layer as well.

Hence you should choose the Classic ELB.

Since the traffic needs to be secure till the EC2 Instances, the SSL termination should occur on the EC2 Instances.

Options A and C are invalid because the Application Load Balancer does not support SSL pass-through.

You need to use a Classic Load balancer.

Option B is incorrect since the encryption is required until the EC2 Instance.

For more information on HTTPS listeners for classic load balancers, please refer to the below URL.

https://docs.aws.amazon.com/elasticloadbalancing/latest/classic/elb-https-load-balancers.html

The best option for securing traffic between the clients and the EC2 instances that communicate via a legacy protocol behind an ELB is to use an Application Load Balancer (ALB) and terminate the SSL connection at the EC2 instances (Option C).

Explanation:

1. Application Load Balancer (ALB) vs. Classic Load Balancer (CLB):

• ALB is a Layer 7 load balancer that can route traffic based on content such as URL or HTTP headers.
• CLB is a Layer 4 load balancer that balances traffic based on IP and port.
• ALB provides better performance, advanced routing capabilities, and more flexible security options.

2. Terminating SSL connection:

• When SSL is terminated, the ELB decrypts the incoming SSL traffic and forwards it in plain HTTP to the backend EC2 instances.
• The reverse process happens for the outgoing traffic. The EC2 instance responds in plain HTTP, and the ELB encrypts it back into SSL before sending it to the client.

3. Security:

• Terminating SSL at the ELB provides security benefits such as SSL offloading and DDoS protection. However, it is not suitable for legacy protocols because they may not support SSL.
• Terminating SSL at the EC2 instances provides end-to-end encryption between the client and the instances, ensuring that the legacy protocol traffic is secure.

Therefore, option C is the best choice for securing traffic between clients and EC2 instances that communicate via a legacy protocol behind an ELB.