- A
Use the 'DependsOn' attribute to ensure the route is created after the NAT gateway.
Why wrong: DependsOn only ensures order, not dynamic updates.
- B
Use the 'AWS::EC2::Route' resource with a 'GatewayId' property that references the NAT gateway using 'Ref'.
Why wrong: 'Ref' returns the logical ID, not the physical ID; and the route would not automatically update if the NAT gateway is replaced.
- C
Use the 'Fn::GetAtt' intrinsic function to retrieve the NAT gateway ID and pass it to the route.
Fn::GetAtt can retrieve the physical ID of the NAT gateway, and if the NAT gateway is replaced, CloudFormation updates the route automatically.
- D
Use an AWS Lambda custom resource to update the route table when the NAT gateway changes.
Why wrong: Custom resource could work but is not the simplest or most automatic.
Quick Answer
The answer is to use the `Fn::GetAtt` intrinsic function to retrieve the NAT gateway ID and pass it to the route. This is correct because `Fn::GetAtt` dynamically extracts the `NatGatewayId` attribute from the NAT gateway resource, allowing you to reference it in the `GatewayId` property of an `AWS::EC2::Route` resource. When the NAT gateway is replaced—due to an update, failure, or stack operation—CloudFormation automatically updates the route with the new ID, ensuring private subnet route tables stay synchronized without manual intervention. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this tests your understanding of CloudFormation’s intrinsic functions for dynamic resource references, a common pattern in high-availability VPC designs. A frequent trap is hardcoding the NAT gateway ID or using `Ref`, which returns the logical name rather than the physical ID; `Fn::GetAtt` is required for attributes like `NatGatewayId`. Memory tip: "GetAtt gets the attribute—don't Ref the name, GetAtt the ID."
ANS-C01 Network Design Practice Question
This ANS-C01 practice question tests your understanding of network design. 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 company is using AWS CloudFormation to deploy a VPC with public and private subnets across multiple Availability Zones. The template includes a NAT gateway in each public subnet. The company wants to ensure that the private subnet route tables automatically update when the NAT gateway ID changes. Which feature should be used?
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
Use the 'Fn::GetAtt' intrinsic function to retrieve the NAT gateway ID and pass it to the route.
Option C is correct because the `Fn::GetAtt` intrinsic function can retrieve the NAT gateway ID (e.g., `Fn::GetAtt: [NatGateway, NatGatewayId]`) and pass it as the `GatewayId` property of an `AWS::EC2::Route` resource. This ensures that when the NAT gateway is replaced (e.g., due to an update or failure), the route automatically updates to reference the new NAT gateway ID, maintaining connectivity for private subnets without manual intervention.
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.
- ✗
Use the 'DependsOn' attribute to ensure the route is created after the NAT gateway.
Why it's wrong here
DependsOn only ensures order, not dynamic updates.
- ✗
Use the 'AWS::EC2::Route' resource with a 'GatewayId' property that references the NAT gateway using 'Ref'.
- ✓
Use the 'Fn::GetAtt' intrinsic function to retrieve the NAT gateway ID and pass it to the route.
- ✗
Use an AWS Lambda custom resource to update the route table when the NAT gateway changes.
Why it's wrong here
Custom resource could work but is not the simplest or most automatic.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse `Ref` (which returns the logical resource name or a default attribute like the AZ) with `Fn::GetAtt` (which returns a specific physical attribute like the NAT gateway ID), leading them to choose Option B incorrectly.
Detailed technical explanation
How to think about this question
Under the hood, `Fn::GetAtt` retrieves the physical resource ID (e.g., `nat-0abc123def456`) from the NAT gateway resource, which CloudFormation resolves at stack creation and update time. When a NAT gateway is replaced (e.g., due to a change in its configuration or an Availability Zone migration), CloudFormation automatically updates the route's `NatGatewayId` property to the new physical ID, ensuring the route table remains valid. This is critical in multi-AZ architectures where NAT gateways are replaced during stack updates or disaster recovery scenarios.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Design — This question tests Network Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use the 'Fn::GetAtt' intrinsic function to retrieve the NAT gateway ID and pass it to the route. — Option C is correct because the `Fn::GetAtt` intrinsic function can retrieve the NAT gateway ID (e.g., `Fn::GetAtt: [NatGateway, NatGatewayId]`) and pass it as the `GatewayId` property of an `AWS::EC2::Route` resource. This ensures that when the NAT gateway is replaced (e.g., due to an update or failure), the route automatically updates to reference the new NAT gateway ID, maintaining connectivity for private subnets without manual intervention.
What should I do if I get this ANS-C01 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: Jun 24, 2026
This ANS-C01 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 ANS-C01 exam.
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