AWS Certified Solutions Architect - Professional (#495)

A benefits enrollment company is hosting a 3-tier web application running in a VPC on AWS which includes a NAT (Network Address Translation) instance in the public Web tier. There is enough provisioned capacity for the expected workload tor the new fiscal year benefit enrollment period plus some extra overhead Enrollment proceeds nicely for two days and then the web tier becomes unresponsive, upon investigation using CloudWatch and other monitoring tools it is discovered that there is an extremely large and unanticipated amount of inbound traffic coming from a set of 15 specific IP addresses over port 80 from a country where the benefits company has no customers. The web tier instances are so overloaded that benefit enrollment administrators cannot even SSH into them. Which activity would be useful in defending against this attack?

Create a custom route table associated with the web tier and block the attacking IP addresses from the IGW (Internet Gateway)
Change the EIP (Elastic IP Address) of the NAT instance in the web tier subnet and update the Main Route Table with the new EIP
Create 15 Security Group rules to block the attacking IP addresses over port 80
Create an inbound NACL (Network Access control list) associated with the web tier subnet with deny rules to block the attacking IP addresses