- A
Hardcode the subnet ID in the template.
Why wrong: Hardcoding makes the template non-reusable across different environments.
- B
Use a mapping (Mappings) to define the subnet ID based on the stack name.
Why wrong: Mappings are for static key-value pairs; subnet IDs are not predictable.
- C
Define a parameter (Parameters) of type AWS::EC2::Subnet::Id and reference it.
Parameters allow the user to specify the subnet ID at stack creation.
- D
Use the Fn::GetAtt function to retrieve the subnet ID from a VPC resource.
Why wrong: Fn::GetAtt returns attributes of a resource, but the subnet is not created in the stack.
Question 1,653 of 1,750
Referencing Subnet IDs in CloudFormation — Using AWS::EC2::Subnet::Id Parameter
This DOP-C02 practice question tests your understanding of sdlc automation. 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 DevOps engineer is creating an AWS CloudFormation template to deploy a stack that includes an Amazon EC2 instance. The instance needs to be launched in a specific subnet. How should the engineer reference the subnet ID in the template?
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
✓
Define a parameter (Parameters) of type AWS::EC2::Subnet::Id and reference it.
Option C is correct because defining a parameter of type `AWS::EC2::Subnet::Id` allows the CloudFormation template to accept a subnet ID as input at stack creation or update time, making the template reusable across different environments without modification. This approach follows infrastructure-as-code best practices by avoiding hardcoded values and enabling parameterized deployments.
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.
- ✗
Hardcode the subnet ID in the template.
Why it's wrong here
Hardcoding makes the template non-reusable across different environments.
- ✗
Use a mapping (Mappings) to define the subnet ID based on the stack name.
Why it's wrong here
Mappings are for static key-value pairs; subnet IDs are not predictable.
- ✓
Define a parameter (Parameters) of type AWS::EC2::Subnet::Id and reference it.
Why this is correct
Parameters allow the user to specify the subnet ID at stack creation.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use the Fn::GetAtt function to retrieve the subnet ID from a VPC resource.
Why it's wrong here
Fn::GetAtt returns attributes of a resource, but the subnet is not created in the stack.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse Fn::GetAtt with the ability to retrieve any resource attribute from any stack, but Fn::GetAtt only works for resources defined in the same template and cannot fetch a subnet ID from an existing VPC resource unless that VPC resource itself outputs the subnet ID.
Detailed technical explanation
How to think about this question
The `AWS::EC2::Subnet::Id` parameter type leverages CloudFormation's built-in validation to ensure the provided value is a valid subnet ID (e.g., subnet-xxxxxxxx), reducing runtime errors. Under the hood, CloudFormation uses the AWS EC2 API to validate the subnet exists and is in the same account and region, but it does not check whether the subnet is in the correct VPC or Availability Zone — that responsibility falls to the template designer. In real-world scenarios, combining this parameter with a Condition or a VPC reference can enforce cross-resource constraints, such as ensuring the subnet belongs to a specific VPC created in the same stack.
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 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.
Visual reference
What to study next
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FAQ
Questions learners often ask
What does this DOP-C02 question test?
SDLC Automation — This question tests SDLC Automation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Define a parameter (Parameters) of type AWS::EC2::Subnet::Id and reference it. — Option C is correct because defining a parameter of type `AWS::EC2::Subnet::Id` allows the CloudFormation template to accept a subnet ID as input at stack creation or update time, making the template reusable across different environments without modification. This approach follows infrastructure-as-code best practices by avoiding hardcoded values and enabling parameterized deployments.
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.
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Last reviewed: Jul 4, 2026
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