- A
Configure the EC2 instance security group to allow inbound traffic from 0.0.0.0/0 on port 443.
Why wrong: This would allow direct access to EC2 instances, bypassing the ALB and its security features. It increases the attack surface.
- B
Use a network ACL to allow inbound HTTP/S traffic only from the ALB's subnet.
Why wrong: Network ACLs are stateless and less granular than security groups. Security groups are the recommended way to control traffic at the instance level.
- C
Place the EC2 instances behind an Amazon CloudFront distribution.
Why wrong: CloudFront is a content delivery network and does not directly replace the ALB for security. It can be used in front of the ALB for additional DDoS protection, but it is not a required security action for the described setup.
- D
Enable AWS WAF on the ALB to filter malicious requests.
AWS WAF provides a web application firewall that can block common attacks like SQL injection and cross-site scripting.
- E
Configure the EC2 instance security group to allow inbound traffic only from the ALB's security group.
This ensures that only traffic that passes through the ALB can reach the EC2 instances, preventing direct access.
DOP-C02 Security and Compliance Practice Question
This DOP-C02 practice question tests your understanding of security and compliance. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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.
Which TWO actions should a DevOps engineer take to secure a web application running on EC2 instances behind an Application Load Balancer? (Choose two.)
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
Enable AWS WAF on the ALB to filter malicious requests.
Correct answers are D and E. Option D: AWS WAF on the ALB helps filter out common web exploits. Option E: Configuring the EC2 security group to allow inbound traffic only from the ALB's security group ensures that direct access to instances is blocked, forcing traffic through the ALB. Option A is incorrect because allowing all inbound traffic (0.0.0.0/0) on port 443 exposes instances directly to the internet, bypassing the ALB. Option B is incorrect: network ACLs are stateless and less granular than security groups; using a NACL to allow traffic from the ALB's subnet is not a recommended practice for instance-level security. Option C is incorrect: placing EC2 instances behind CloudFront is a content delivery optimization, not a security measure to protect the application layer; it does not replace the need for WAF or security group restrictions.
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.
- ✗
Configure the EC2 instance security group to allow inbound traffic from 0.0.0.0/0 on port 443.
Why it's wrong here
This would allow direct access to EC2 instances, bypassing the ALB and its security features. It increases the attack surface.
- ✗
Use a network ACL to allow inbound HTTP/S traffic only from the ALB's subnet.
Why it's wrong here
Network ACLs are stateless and less granular than security groups. Security groups are the recommended way to control traffic at the instance level.
- ✗
Place the EC2 instances behind an Amazon CloudFront distribution.
Why it's wrong here
CloudFront is a content delivery network and does not directly replace the ALB for security. It can be used in front of the ALB for additional DDoS protection, but it is not a required security action for the described setup.
- ✓
Enable AWS WAF on the ALB to filter malicious requests.
- ✓
Configure the EC2 instance security group to allow inbound traffic only from the ALB's security group.
Why this is correct
This ensures that only traffic that passes through the ALB can reach the EC2 instances, preventing direct access.
Related concept
CIDR notation defines the prefix length.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
Visual reference
Quick reference
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
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 DOP-C02 subnetting questions on CIDR, address ranges, and subnet selection.
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Security and Compliance — study guide chapter
Learn the concepts, then practise the questions
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Security and Compliance practice questions
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FAQ
Questions learners often ask
What does this DOP-C02 question test?
Security and Compliance — This question tests Security and Compliance — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Enable AWS WAF on the ALB to filter malicious requests. — Correct answers are D and E. Option D: AWS WAF on the ALB helps filter out common web exploits. Option E: Configuring the EC2 security group to allow inbound traffic only from the ALB's security group ensures that direct access to instances is blocked, forcing traffic through the ALB. Option A is incorrect because allowing all inbound traffic (0.0.0.0/0) on port 443 exposes instances directly to the internet, bypassing the ALB. Option B is incorrect: network ACLs are stateless and less granular than security groups; using a NACL to allow traffic from the ALB's subnet is not a recommended practice for instance-level security. Option C is incorrect: placing EC2 instances behind CloudFront is a content delivery optimization, not a security measure to protect the application layer; it does not replace the need for WAF or security group restrictions.
What should I do if I get this DOP-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 DOP-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
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