ANS-C01 Network Design Practice Question
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?
⚠ Common exam trap
A common mix-up: 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.
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.
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.
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.
Why it's wrong here
This still has a single point of failure for the NAT Gateway and adds VPN complexity.
- ✓
Deploy one NAT Gateway in each AZ that contains private subnets, and update the route tables accordingly.
Why this is correct
This ensures each AZ is independent; if one NAT Gateway fails, only that AZ loses internet access.
- ✗
Use a NAT instance in an Auto Scaling group across multiple AZs instead of a NAT Gateway.
Why it's wrong here
NAT instances are not fully managed and require maintenance; NAT Gateway is preferred for high availability.
- ✗
Create a second VPC with a NAT Gateway and peer the VPCs to share the NAT Gateway.
Why it's wrong here
VPC peering does not allow transitive routing to a NAT Gateway across VPCs.
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Same concept, more angles
1 more way 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.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.