B. Create security group rules using the security group ID as the source or destination. This way, the security team can ensure that the least privileged access is given to the application tiers by allowing only the necessary communication between the security groups. For example, the web tier security group should only allow incoming traffic from the load balancer security group and outgoing traffic to the application tier security group. This approach provides a more granular and secure way to control traffic between the different tiers of the application and also allows for easy modification of access if needed. It's also worth noting that it's good practice to minimize the number of open ports and protocols, and use security groups as a first line of defense, in addition to network access control lists (ACLs) to control traffic between subnets.

By using security group IDs, the ingress and egress rules can be restricted to only allow traffic from the necessary source or destination, and to deny all other traffic. This ensures that only the minimum required traffic is allowed between the application tiers. Option A is not the best choice because using the instance ID as the source or destination would allow traffic from any instance with that ID, which may not be limited to the specific application tier. Option C is also not the best choice because using VPC CIDR blocks would allow traffic from any IP address within the VPC, which may not be limited to the specific application tier. Option D is not the best choice because using subnet CIDR blocks would allow traffic from any IP address within the subnet, which may not be limited to the specific application tier.

Create security group rules using the security group ID as the source or destination. This way, the security team can ensure that the least privileged access is given to the application tiers by allowing only the necessary communication between the security groups. For example, the web tier security group should only allow incoming traffic from the load balancer security group and outgoing traffic to the application tier security group. This approach provides a more granular and secure way to control traffic between the different tiers of the application and also allows for easy modification of access if needed. It's also worth noting that it's good practice to minimize the number of open ports and protocols, and use security groups as a first line of defense, in addition to network access control lists (ACLs) to control traffic between subnets.

A. would limit the traffic based on specific instances, which may not be the most suitable solution for applying the principle of least privilege between application tiers. B. By using security group IDs in the rules, you can precisely control the traffic between application tiers, allowing only the necessary communication and adhering to the principle of least privilege. C. would apply broad rules based on the entire VPC CIDR blocks, which may not provide the necessary level of granularity required for secure communication between specific application tiers. D. would limit the traffic based on subnet CIDR blocks, which may not be sufficient for ensuring proper security between application tiers. In summary, using security group IDs (Option B) is the recommended approach as it allows for precise control of traffic between application tiers, aligning with the principle of least privilege.

I vote for option B.

. Create security group rules using the security group ID as the source or destination

Security Group Rulesapply to instances https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/security-group-rules.html

Correct answer is B

https://www.examtopics.com/discussions/amazon/view/46463-exam-aws-certified-solutions-architect-associate-saa-c02/

B right https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/security-group-rules.html