- A
Change the EC2 instance security group to allow inbound traffic on port 8080 from 0.0.0.0/0, and rely on the subnet network ACL to block traffic.
Why wrong: This would allow direct internet access to instances, making them vulnerable.
- B
Add a rule to the EC2 security group that denies inbound traffic from 0.0.0.0/0 on port 8080.
Why wrong: Security groups only support allow rules; you cannot add a deny rule.
- C
Modify the ALB security group to remove the inbound rule for port 8080 from 0.0.0.0/0, and configure the ALB listener to forward traffic from port 80/443 to port 8080 on the target group.
This correctly restricts internet access to the ALB on standard ports and allows the ALB to forward to port 8080.
- D
Place the EC2 instances in a public subnet and use a network ACL to block inbound traffic on port 8080 from the internet.
Why wrong: Placing instances in public subnet exposes them to internet; NACLs are stateless and less secure.
Quick Answer
The answer is to modify the ALB security group by removing the inbound rule for port 8080 from 0.0.0.0/0, then configure the ALB listener to accept traffic on standard ports 80 or 443 and forward it to port 8080 on the target group. This is correct because the ALB acts as the internet-facing entry point, so its security group should only allow inbound HTTP/HTTPS traffic from the internet on standard ports, not the application port itself. The ALB then translates that traffic to port 8080 internally, ensuring the EC2 instances remain isolated in private subnets behind the NAT Gateway. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of security group layering and ALB listener configuration—a common trap is leaving the application port open on the ALB security group, which directly exposes the backend. The key insight is that the ALB’s security group controls what the internet sees, while the listener controls internal routing. Memory tip: ALB security groups should only expose standard web ports; the listener handles the port translation to your application.
SCS-C02 Infrastructure Security Practice Question
This SCS-C02 practice question tests your understanding of infrastructure security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company runs a multi-tier web application on AWS. The web tier uses an Application Load Balancer (ALB) in a public subnet, and the application tier runs on EC2 instances in private subnets. The security team recently ran a vulnerability scan and found that the application instances are accessible from the internet on port 8080. The EC2 instances have a security group that allows inbound traffic on port 8080 from the ALB's security group only. However, the ALB's security group allows inbound traffic on port 8080 from 0.0.0.0/0. The architecture also includes a NAT Gateway for outbound internet access from private subnets. The security engineer needs to ensure that only the ALB can communicate with the application instances on port 8080, and that the application instances cannot be directly accessed from the internet. What should the security engineer do?
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
Modify the ALB security group to remove the inbound rule for port 8080 from 0.0.0.0/0, and configure the ALB listener to forward traffic from port 80/443 to port 8080 on the target group.
The ALB's security group should not allow inbound from 0.0.0.0/0 on the application port. Instead, the ALB should listen on port 80/443 from the internet and forward to port 8080 on the instances. The ALB security group rule should be removed, and the listener should be configured on standard ports. The EC2 security group is already correct.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Change the EC2 instance security group to allow inbound traffic on port 8080 from 0.0.0.0/0, and rely on the subnet network ACL to block traffic.
Why it's wrong here
This would allow direct internet access to instances, making them vulnerable.
- ✗
Add a rule to the EC2 security group that denies inbound traffic from 0.0.0.0/0 on port 8080.
Why it's wrong here
Security groups only support allow rules; you cannot add a deny rule.
- ✓
Modify the ALB security group to remove the inbound rule for port 8080 from 0.0.0.0/0, and configure the ALB listener to forward traffic from port 80/443 to port 8080 on the target group.
Why this is correct
This correctly restricts internet access to the ALB on standard ports and allows the ALB to forward to port 8080.
Related concept
CIDR notation defines the prefix length.
- ✗
Place the EC2 instances in a public subnet and use a network ACL to block inbound traffic on port 8080 from the internet.
Why it's wrong here
Placing instances in public subnet exposes them to internet; NACLs are stateless and less secure.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
- CIDR notation defines the prefix length.
- Block size helps identify subnet boundaries.
- Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
- The required host count determines the smallest suitable subnet.
TExam Day Tips
- Write the block size before choosing the subnet.
- Check whether the question asks for hosts, subnets or a specific address range.
- Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SCS-C02 subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Questions learners often ask
What does this SCS-C02 question test?
Infrastructure Security — This question tests Infrastructure Security — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Modify the ALB security group to remove the inbound rule for port 8080 from 0.0.0.0/0, and configure the ALB listener to forward traffic from port 80/443 to port 8080 on the target group. — The ALB's security group should not allow inbound from 0.0.0.0/0 on the application port. Instead, the ALB should listen on port 80/443 from the internet and forward to port 8080 on the instances. The ALB security group rule should be removed, and the listener should be configured on standard ports. The EC2 security group is already correct.
What should I do if I get this SCS-C02 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SCS-C02 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Last reviewed: Jun 20, 2026
This SCS-C02 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 SCS-C02 exam.
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