- A
Place the EC2 instances in a private subnet with no internet gateway attachment.
Private subnets prevent direct internet access to instances.
- B
Attach an Internet Gateway to the VPC and route the private subnet to it.
Why wrong: Private subnets should not have routes to an Internet Gateway.
- C
Configure a network ACL on the private subnet to allow inbound traffic on all ephemeral ports.
Why wrong: Security groups are sufficient; NACLs are stateless and not needed for this scenario.
- D
Configure the security group for the EC2 instances to allow traffic only from the ALB's security group.
This ensures only the ALB can reach the instances.
- E
Set up an AWS Direct Connect connection for the instances to access the internet.
Why wrong: Direct Connect is for private connectivity to on-premises, not for inbound web traffic.
Quick Answer
The correct answer is to place EC2 instances in private subnets without an internet gateway and configure their security group to allow traffic only from the ALB’s security group. This architecture ensures the application is completely isolated from the internet, as private subnets have no direct egress or ingress path, while the security group rule creates a tightly scoped, identity-based trust between the load balancer and the instances. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding of defense-in-depth for secure VPC architecture with private subnets and ALB, often appearing as a distractor where candidates mistakenly add a NAT gateway or open the instance security group to 0.0.0.0/0. A common trap is thinking a NAT gateway is needed for outbound traffic—but the requirement here is isolation, not internet access. Remember the memory tip: “Private subnet, no IGW; SG only from ALB—that’s the secure VPC key.”
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.
A security engineer is designing a secure VPC architecture for a web application. The application must be isolated from the internet and only accessible through a load balancer. Which TWO actions should the engineer take?
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
Place the EC2 instances in a private subnet with no internet gateway attachment.
Option A is correct because placing EC2 instances in a private subnet without an internet gateway ensures they have no direct path to the internet, meeting the isolation requirement. This forces all traffic to and from the instances to go through the load balancer, which is the only entry point for the application.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Place the EC2 instances in a private subnet with no internet gateway attachment.
Why this is correct
Private subnets prevent direct internet access to instances.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Attach an Internet Gateway to the VPC and route the private subnet to it.
Why it's wrong here
Private subnets should not have routes to an Internet Gateway.
- ✗
Configure a network ACL on the private subnet to allow inbound traffic on all ephemeral ports.
Why it's wrong here
Security groups are sufficient; NACLs are stateless and not needed for this scenario.
- ✓
Configure the security group for the EC2 instances to allow traffic only from the ALB's security group.
Why this is correct
This ensures only the ALB can reach the instances.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Set up an AWS Direct Connect connection for the instances to access the internet.
Why it's wrong here
Direct Connect is for private connectivity to on-premises, not for inbound web traffic.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the need for a network ACL to allow ephemeral ports (Option C) as a necessary step for inbound traffic from the ALB, but security groups handle stateful filtering and the ALB's security group is the correct source, while network ACLs are stateless and require explicit rules for both inbound and outbound traffic, which is not the primary action for isolation.
Trap categories for this question
Scenario analysis trap
Security groups are sufficient; NACLs are stateless and not needed for this scenario.
Detailed technical explanation
How to think about this question
In a secure VPC architecture, private subnets have no route to an internet gateway, so instances use a NAT gateway or load balancer for outbound traffic. The security group for EC2 instances should reference the ALB's security group as the source, allowing only traffic that has passed through the load balancer, which enforces application-layer security and prevents direct access. This pattern is commonly used in multi-tier web applications to ensure the web tier is the only public-facing component.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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Security and Compliance — study guide chapter
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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 — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Place the EC2 instances in a private subnet with no internet gateway attachment. — Option A is correct because placing EC2 instances in a private subnet without an internet gateway ensures they have no direct path to the internet, meeting the isolation requirement. This forces all traffic to and from the instances to go through the load balancer, which is the only entry point for the application.
What should I do if I get this DOP-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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Last reviewed: Jun 24, 2026
This DOP-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 DOP-C02 exam.
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