The answer is the EC2 instance depends on the Elastic IP, and the Elastic IP depends on the EC2 instance. This creates a classic circular dependency in CloudFormation because the Elastic IP resource (AWS::EC2::EIP) uses an InstanceId property that references the EC2 instance, while the EC2 instance itself has a DependsOn or a direct reference back to the Elastic IP, often through an association resource. CloudFormation cannot determine which resource to create first when each requires the other to exist, leading to the stack creation failure. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding of resource dependency resolution and the common trap of mixing explicit DependsOn with implicit references like InstanceId. A memory tip: if your Elastic IP points to an instance and your instance points back to the IP, you have created a dependency loop—break it by removing the explicit DependsOn from the instance and letting CloudFormation infer the order from the association resource alone.
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 uses AWS CloudFormation to manage infrastructure. The stack creation fails with the error: 'Circular dependency between resources'. The template includes an EC2 instance, an Elastic IP, and an internet gateway. The instance is associated with the Elastic IP, and the Elastic IP uses the internet gateway for the VPC. Which resource relationship is MOST likely causing the circular dependency?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The EC2 instance depends on the Elastic IP, and the Elastic IP depends on the EC2 instance.
Option C is correct because the circular dependency arises when the EC2 instance depends on the Elastic IP (via an Association resource) and the Elastic IP depends on the EC2 instance (via the InstanceId property). CloudFormation cannot resolve the creation order when two resources each require the other to exist first. This is a classic circular dependency in CloudFormation templates when using an AWS::EC2::EIP with an InstanceId that references the EC2 instance, while the instance itself has a DependsOn or a reference to the Elastic IP.
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.
✗
The security group depends on the EC2 instance, and the EC2 instance depends on the security group.
Why it's wrong here
Security group does not depend on EC2 instance.
✗
The Elastic IP depends on the internet gateway, and the internet gateway depends on the Elastic IP.
The EC2 instance depends on the Elastic IP, and the Elastic IP depends on the EC2 instance.
Why this is correct
This creates a circular dependency.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The internet gateway depends on the VPC, and the VPC depends on the internet gateway.
Why it's wrong here
No circular dependency between internet gateway and VPC.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse the Elastic IP's dependency on the internet gateway (which is not direct) with the mutual dependency between the EC2 instance and the Elastic IP when the EIP uses the InstanceId property.
Detailed technical explanation
How to think about this question
Under the hood, CloudFormation uses a directed acyclic graph (DAG) to determine resource creation order. When a resource references another resource's logical ID (e.g., !Ref or !GetAtt), CloudFormation automatically adds a dependency. A circular dependency occurs when two resources each reference the other, creating a cycle in the DAG. In real-world scenarios, this often happens when an EC2 instance needs an Elastic IP, and the Elastic IP is configured with the instance's InstanceId, causing a mutual dependency that must be broken by using a separate AWS::EC2::EIPAssociation resource.
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.
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: The EC2 instance depends on the Elastic IP, and the Elastic IP depends on the EC2 instance. — Option C is correct because the circular dependency arises when the EC2 instance depends on the Elastic IP (via an Association resource) and the Elastic IP depends on the EC2 instance (via the InstanceId property). CloudFormation cannot resolve the creation order when two resources each require the other to exist first. This is a classic circular dependency in CloudFormation templates when using an AWS::EC2::EIP with an InstanceId that references the EC2 instance, while the instance itself has a DependsOn or a reference to the Elastic IP.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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