What mechanism will allow the company to implement all required network rules without incurring additional cost?
Configure AWS WAF rules to implement the required rules.
Use the operating system built-in, host-based firewall to implement the required rules.
Use a NAT gateway to control ingress and egress according to the requirements.
Launch an EC2-based firewall product from the AWS Marketplace, and implement the required rules in that product.
Explanations:
AWS WAF is designed for web application protection and does not manage ingress or egress traffic for EC2 instances or control network connectivity between EC2 instances. It primarily deals with HTTP/S traffic.
The operating system’s built-in, host-based firewall (such as iptables on Linux or Windows Firewall on Windows) can be used to enforce network rules directly on the instances. This provides flexibility in managing complex rules without exceeding security group or NACL limits and does not incur additional costs.
A NAT gateway is used to allow instances in private subnets to initiate outbound connections to the internet but does not control ingress and egress based on complex security rules for EC2 instance-to-instance communications. It does not address the requirements of complex connectivity rules.
Although using an EC2-based firewall from the AWS Marketplace could provide the required functionality, it would incur additional costs, which the company wants to avoid. It also involves managing additional infrastructure and does not align with the objective of not incurring extra cost.
I evaluate that the answer is:
Use the operating system built-in, host-based firewall to implement the required rules.