ANS-C01 Network Security, Compliance and Governance Practice Question
A company runs a web application on EC2 instances in an Auto Scaling group behind an Application Load Balancer. The application must only accept traffic from known corporate IP addresses, but the company also needs to allow healthy traffic from AWS health checkers. Which architecture meets these requirements securely?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure the Application Load Balancer's security group to allow inbound from corporate IPs, and the EC2 instances' security group to allow inbound from the ALB's security group.
The correct approach is to use security groups. The ALB security group should allow inbound from corporate IPs, and the EC2 instances' security group should allow inbound only from the ALB's security group. This ensures that traffic from the internet first passes through the ALB, which performs health checks using its private IPs (which are part of the ALB's security group). Option B is incorrect because having multiple target groups does not control traffic filtering. Option C (WAF) can filter by IP but still requires allowing health check traffic, and it adds unnecessary complexity. Option D (NACL) is stateless and would require complex rules to allow return traffic and health checks, making it less secure and manageable.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Configure the Application Load Balancer's security group to allow inbound from corporate IPs, and the EC2 instances' security group to allow inbound from the ALB's security group.
Why this is correct
This ensures that only traffic through the ALB (including health checks) reaches the instances, and the ALB only accepts corporate IP traffic.
- ✗
Create two target groups: one for corporate traffic and one for health check traffic, each with different security groups.
Why it's wrong here
Health checks are sent by the ALB itself, not by separate target groups; this approach doesn't solve the problem.
- ✗
Use AWS WAF on the ALB to create an IP set containing corporate IPs, and allow all traffic from ALB to instances.
Why it's wrong here
AWS WAF can filter by IP, but health checker traffic from the ALB is still allowed; however, WAF adds unnecessary cost and complexity compared to security groups.
- ✗
Use a network ACL on the VPC subnet to allow inbound traffic from corporate IPs and AWS health checker IP ranges.
Why it's wrong here
A network ACL is stateless, so while it can filter inbound traffic from corporate IPs and AWS health checkers, it cannot track return traffic; the ALB would send responses back through ephemeral ports, requiring explicit outbound rules that are difficult to manage securely. This option is tempting because network ACLs are often used for IP-based subnet filtering, and they would be correct in a scenario where the application itself, rather than a load balancer, directly receives traffic and stateless filtering is acceptable.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This ANS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the ANS-C01 exam.