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Question 552 of 1,740

Configuration Management and IaC →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is to add an AWS::EC2::SecurityGroupIngress rule that references the instance’s network interface using Fn::GetAtt on the network interface resource. This resolves the circular dependency because the security group ingress rule no longer depends on the EC2 instance directly; instead, it depends on the network interface, which is created as part of the instance launch but can be referenced by its logical ID without creating a loop. The original circular dependency occurs because the security group references the instance’s private IP (unknown until creation), while the instance references the security group—creating a deadlock. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this tests your understanding of CloudFormation dependency chains and the use of intermediate resources like ENIs to break cycles. A common trap is assuming Ref on the instance returns the IP, but it returns the instance ID. Memory tip: think “ENI breaks the tie”—by attaching the ingress rule to the network interface, you decouple the creation order.

DOP-C02 Configuration Management and IaC Practice Question

This DOP-C02 practice question tests your understanding of configuration management and iac. 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 DevOps engineer is troubleshooting a CloudFormation stack that fails to create. The error message indicates a 'circular dependency' between two resources: a security group and an EC2 instance. The security group contains an ingress rule that references the instance's private IP address, which is not known until the instance is created. The instance's network interface uses the security group. What change should the engineer make to resolve the circular dependency?

Question 1hardmultiple choice

Full question →

A
Create the EC2 instance first without a security group, then attach the security group after creation.
Why wrong: D: This would require two separate stacks or a custom resource, not a single template.
B
Add an AWS::EC2::SecurityGroupIngress rule that references the instance's network interface using Fn::GetAtt on the network interface resource.
C: By creating the network interface as a separate resource and referencing its primary private IP, you can order the dependencies correctly.
C
Hardcode the instance's private IP address in the security group rule.
Why wrong: A: Hardcoding is not dynamic and may not be accurate for future replacements.
D
Use the Ref function on the EC2 instance to get its private IP address.
Why wrong: B: Ref on an EC2 instance returns the instance ID, not the IP.

Full breakdown with real-world context →

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

✓

Add an AWS::EC2::SecurityGroupIngress rule that references the instance's network interface using Fn::GetAtt on the network interface resource.

Option C is correct because by using a VPC endpoint on the security group rule, you can reference the instance's network interface after creation, breaking the circular dependency. Option A is wrong because hardcoding the IP is not dynamic and may not be the correct IP. Option B is wrong because Ref on the instance returns the instance ID, not the IP. Option D is wrong because depending on the network interface still requires the interface to exist, which depends on the instance.

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.

✗
Create the EC2 instance first without a security group, then attach the security group after creation.
Why it's wrong here
D: This would require two separate stacks or a custom resource, not a single template.
✓
Add an AWS::EC2::SecurityGroupIngress rule that references the instance's network interface using Fn::GetAtt on the network interface resource.
Why this is correct
C: By creating the network interface as a separate resource and referencing its primary private IP, you can order the dependencies correctly.
Related concept
Read the scenario before looking for a memorised answer.
✗
Hardcode the instance's private IP address in the security group rule.
Why it's wrong here
A: Hardcoding is not dynamic and may not be accurate for future replacements.
✗
Use the Ref function on the EC2 instance to get its private IP address.
Why it's wrong here
B: Ref on an EC2 instance returns the instance ID, not the IP.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.

Detailed technical explanation

How to think about this question

This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.

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.
Use explanations to understand the rule behind the answer.

TExam Day Tips

Underline the problem statement mentally.
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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.

What to study next

Got this wrong? Here's your next step.

Identify which DOP-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.

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FAQ

Questions learners often ask

What does this DOP-C02 question test?

Configuration Management and IaC — This question tests Configuration Management and IaC — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: Add an AWS::EC2::SecurityGroupIngress rule that references the instance's network interface using Fn::GetAtt on the network interface resource. — Option C is correct because by using a VPC endpoint on the security group rule, you can reference the instance's network interface after creation, breaking the circular dependency. Option A is wrong because hardcoding the IP is not dynamic and may not be the correct IP. Option B is wrong because Ref on the instance returns the instance ID, not the IP. Option D is wrong because depending on the network interface still requires the interface to exist, which depends on the instance.

What should I do if I get this DOP-C02 question wrong?

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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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.