The answer is to use the Fn::ImportValue intrinsic function in the application stack to import the security group ID from the VPC stack's exports. This approach is correct because Fn::ImportValue creates a live cross-stack reference that automatically resolves to the latest exported value whenever the source stack is updated, ensuring dependent stacks always receive the current output without manual intervention. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding of CloudFormation cross-stack reference best practices, specifically how to decouple stacks while maintaining dynamic dependencies—a common trap is confusing nested stacks with cross-stack exports, as nested stacks do not automatically propagate output changes. Remember that Fn::ImportValue is the only way to create a true, live dependency between independent stacks, whereas nested stacks require explicit parameter updates. Memory tip: "Import to stay current, nest to stay separate."
DOP-C02 SDLC Automation Practice Question
This DOP-C02 practice question tests your understanding of sdlc automation. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 large enterprise is using AWS CloudFormation to manage their infrastructure. They have a master template that orchestrates nested stacks for different components: VPC, application, and database. The VPC stack creates subnets, route tables, and security groups. The application stack creates EC2 instances and an Application Load Balancer. The database stack creates an RDS instance. The master template uses parameters to pass configuration values. Recently, when updating the application stack, the update failed because the security group ID from the VPC stack changed, and the application stack references the old security group ID. The team wants to ensure that when the VPC stack is updated, dependent stacks are automatically updated to use the new outputs. Which approach should they take?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use the Fn::ImportValue intrinsic function in the application stack to import the security group ID from the VPC stack's exports.
Option B is correct because using Fn::ImportValue to import exported outputs from other stacks ensures that the dependent stack always gets the latest value. Option A is wrong because hardcoding is error-prone. Option C is wrong because CloudFormation does not automatically update nested stacks when parent outputs change; the parent stack must be updated. Option D is wrong because cross-stack references using Fn::ImportValue are the recommended pattern.
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.
✓
Use the Fn::ImportValue intrinsic function in the application stack to import the security group ID from the VPC stack's exports.
Why this is correct
Fn::ImportValue allows stacks to reference exported outputs from other stacks.
Use the Fn::GetAtt intrinsic function in the application stack to directly reference the security group from the VPC stack.
Why it's wrong here
Fn::GetAtt only works within the same stack, not cross-stack.
✗
Hardcode the security group ID in the application template to avoid changes.
Why it's wrong here
Hardcoding defeats the purpose of dynamic infrastructure.
✗
Configure the master template to automatically update all nested stacks whenever any output changes.
Why it's wrong here
CloudFormation does not support automatic propagation of output changes to nested stacks.
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.
Trap categories for this question
Command / output trap
CloudFormation does not support automatic propagation of output changes to nested stacks.
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 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.
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.
SDLC Automation — This question tests SDLC Automation — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Use the Fn::ImportValue intrinsic function in the application stack to import the security group ID from the VPC stack's exports. — Option B is correct because using Fn::ImportValue to import exported outputs from other stacks ensures that the dependent stack always gets the latest value. Option A is wrong because hardcoding is error-prone. Option C is wrong because CloudFormation does not automatically update nested stacks when parent outputs change; the parent stack must be updated. Option D is wrong because cross-stack references using Fn::ImportValue are the recommended pattern.
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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