How does an NACL differ from a security group in AWS?

The correct answer highlights a key functional difference between Network Access Control Lists (NACLs) and security groups in AWS. NACLs operate at the subnet level, which means they apply rules to all traffic entering and exiting a subnet, impacting the flow of traffic for all instances within that subnet. They provide an additional layer of security by allowing both inbound and outbound traffic filtering, which enables administrators to define specific rules for both types of traffic.

In contrast, security groups function at the instance level and primarily control inbound traffic to instances. They allow for stateful filtering, meaning that if an incoming request is allowed, the response is automatically permitted regardless of outbound rules. However, security groups do not filter outbound traffic based on incoming requests, making them less flexible in certain scenarios compared to NACLs.

This distinction is essential for network security management in AWS, as choosing the right mechanism depends on the specific networking needs and security requirements of a deployment. Understanding how NACLs and security groups operate at different levels and with different filtering capabilities assists in designing secure and efficient cloud architectures.