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SAA-C03 Practice Question 63: Network Firewall Egress Domains

AWS Certified Solutions Architect – Associate (SAA-C03) · Test 7 · question 3 of 10

Network Securitymedium

Instances in a VPC's private subnets reach the internet through a NAT gateway. A new policy states that these instances may open outbound HTTPS connections only to an approved list of external domain names: a package mirror and three partner APIs. Those endpoints sit behind content delivery networks whose IP addresses change constantly, so an address-based allow list is not workable. The control must be enforced at the VPC perimeter, with nothing installed on the instances.

Which solution meets the requirement?

Select one answer
Show answer and explanation

Answer:

  • A. Deploy AWS Network Firewall in the VPC, write a stateful rule group that allows only the approved domain names, and route outbound traffic through the firewall endpoints

Network Firewall is a managed, stateful firewall for a VPC that filters traffic at the perimeter, including traffic heading out through an internet gateway or NAT gateway. Its stateful engine supports domain name filtering, so an allow list of domains is exactly the rule type it is built for, and stateful protocol detection identifies HTTPS independently of port. Traffic is steered to the firewall endpoints through VPC route tables, which means the control is applied to every instance in the routed subnets with no agent installed anywhere.

Option B asks security groups to do something they cannot. A security group rule's source or destination is an IPv4 or IPv6 address, a CIDR block, a prefix list ID or another security group ID; there is no field that accepts a domain name.

Option C fails for the same reason, and adds two more. Network ACL rules are also CIDR-based, they are stateless so each direction needs matching rules, and a list of "everything except these domains" is not expressible as deny rules in the first place.

Option D is the wrong direction and the wrong attachment point. AWS WAF inspects inbound HTTP requests to resources such as CloudFront distributions, Application Load Balancers and API Gateway APIs; it cannot be associated with a NAT gateway and does not filter traffic your instances originate.

Reference: What is AWS Network Firewall?

Practice Test 7 ›

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