- A
Deploy a single NAT Gateway in one AZ and use a VPN to an on-premises internet gateway as backup.
Why wrong: This still has a single point of failure for the NAT Gateway and adds VPN complexity.
- B
Deploy one NAT Gateway in each AZ that contains private subnets, and update the route tables accordingly.
This ensures each AZ is independent; if one NAT Gateway fails, only that AZ loses internet access.
- C
Use a NAT instance in an Auto Scaling group across multiple AZs instead of a NAT Gateway.
Why wrong: NAT instances are not fully managed and require maintenance; NAT Gateway is preferred for high availability.
- D
Create a second VPC with a NAT Gateway and peer the VPCs to share the NAT Gateway.
Why wrong: VPC peering does not allow transitive routing to a NAT Gateway across VPCs.
NAT Gateway High Availability — Multi-AZ Deployment | AWS Advanced Networking Specialty Explained
This ANS-C01 practice question tests your understanding of network design. 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 company has a VPC with public and private subnets. The private subnets need to access the internet for software updates. The company wants to use a single NAT Gateway for all private subnets to reduce costs, but the NAT Gateway is in a single Availability Zone (AZ). The network architect is concerned about single points of failure. Which design best addresses high availability while still using the minimum number of NAT Gateways?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"minimum / minimize"Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
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
Deploy one NAT Gateway in each AZ that contains private subnets, and update the route tables accordingly.
Option B is correct because deploying one NAT Gateway per Availability Zone (AZ) that contains private subnets ensures that if an AZ fails, the private subnets in other AZs still have internet access via their local NAT Gateway. This design provides high availability while using the minimum number of NAT Gateways necessary to cover all AZs with private subnets, avoiding a single point of failure without over-provisioning.
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.
- ✗
Deploy a single NAT Gateway in one AZ and use a VPN to an on-premises internet gateway as backup.
- ✓
Deploy one NAT Gateway in each AZ that contains private subnets, and update the route tables accordingly.
- ✗
Use a NAT instance in an Auto Scaling group across multiple AZs instead of a NAT Gateway.
- ✗
Create a second VPC with a NAT Gateway and peer the VPCs to share the NAT Gateway.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a single NAT Gateway is sufficient for high availability if placed in a multi-AZ setup, but they overlook that NAT Gateway is an AZ-scoped resource and does not automatically fail over to another AZ, so a single NAT Gateway remains a single point of failure.
Detailed technical explanation
How to think about this question
NAT Gateways are highly available within a single AZ but not across AZs; if the AZ hosting the NAT Gateway fails, all private subnets lose internet access unless a NAT Gateway exists in another AZ. The recommended design uses one NAT Gateway per AZ with private subnets, and route tables in each private subnet point to the NAT Gateway in the same AZ to avoid cross-AZ data transfer costs and minimize latency. This aligns with AWS best practices for high availability while minimizing the number of NAT Gateways.
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 startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
Visual reference
What to study next
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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: Deploy one NAT Gateway in each AZ that contains private subnets, and update the route tables accordingly. — Option B is correct because deploying one NAT Gateway per Availability Zone (AZ) that contains private subnets ensures that if an AZ fails, the private subnets in other AZs still have internet access via their local NAT Gateway. This design provides high availability while using the minimum number of NAT Gateways necessary to cover all AZs with private subnets, avoiding a single point of failure without over-provisioning.
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.
Are there clue words in this question I should notice?
Yes — watch for: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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Same concept, more angles
1 more ways this is tested on ANS-C01
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company has a VPC with public and private subnets. They want to provide outbound internet access to instances in private subnets while preventing inbound internet traffic. The solution must be highly available and scale automatically. Which combination of services should be used?
hard- A.NAT instances in each Availability Zone
- B.VPC endpoint for S3 and DynamoDB
- C.Internet Gateway attached to the VPC with route tables pointing to the Internet Gateway
- ✓ D.NAT Gateway in each Availability Zone with route tables pointing to the NAT Gateway
Why D: D is correct because a NAT Gateway in each Availability Zone provides highly available, automatically scaling outbound internet access for private subnets while blocking unsolicited inbound traffic. NAT Gateways are managed by AWS, scale up to 45 Gbps, and are redundant per AZ, meeting the requirements for high availability and automatic scaling without manual intervention.
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Last reviewed: Jul 4, 2026
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