The answer is creating VPC endpoints for S3 and DynamoDB in the private subnets and updating the route tables, as this is the most cost-effective solution. VPC endpoints allow private subnet resources to access these services over the AWS network without traversing the internet, eliminating the need for a NAT gateway, which incurs both hourly charges and per-GB data processing fees. Since VPC endpoints themselves have no hourly cost and only minimal data processing charges, they directly achieve the goal of minimizing data transfer costs while maintaining private connectivity. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of cost optimization in hybrid network designs, often appearing as a trap where candidates mistakenly choose a NAT gateway for private subnet access. A common memory tip is “endpoints are free, NATs are not”—remember that Gateway Endpoints for S3 and DynamoDB are a zero-cost entry point for private access, making them the default choice for cost-conscious architectures.
ANS-C01 Network Security, Compliance and Governance Practice Question
This ANS-C01 practice question tests your understanding of network security, compliance and governance. 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 designing a VPC with public and private subnets. The private subnets need to access Amazon S3 and Amazon DynamoDB. The company wants to minimize data transfer costs and avoid using a NAT gateway. What is the MOST cost-effective solution?
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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create VPC endpoints for S3 and DynamoDB in the private subnets and update route tables
Option B is correct because VPC endpoints for S3 and DynamoDB are free to create and avoid NATgateway costs. Option A is wrong because NAT gateway incurs hourly charges and data processing fees. Option C is wrong because an HTTP proxy is unnecessary and adds complexity. Option D is wrong because it incurs NAT costs.
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.
✗
Set up an HTTP proxy in the private subnets and configure the applications to use it
Why it's wrong here
Proxy adds complexity and cost; VPC endpoints are simpler.
✗
Use a NAT instance instead of a NAT gateway
Why it's wrong here
NAT instance still incurs EC2 costs and management overhead.
✓
Create VPC endpoints for S3 and DynamoDB in the private subnets and update route tables
Why this is correct
VPC endpoints are free and provide private connectivity without NATgateway.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
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.
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 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.
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 ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Network Security, Compliance and Governance — This question tests Network Security, Compliance and Governance — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Create VPC endpoints for S3 and DynamoDB in the private subnets and update route tables — Option B is correct because VPC endpoints for S3 and DynamoDB are free to create and avoid NAT gateway costs. Option A is wrong because NAT gateway incurs hourly charges and data processing fees. Option C is wrong because an HTTP proxy is unnecessary and adds complexity. Option D is wrong because it incurs NAT costs.
What should I do if I get this ANS-C01 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 ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
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?
CIDR notation defines the prefix length.
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Question Discussion
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