The correct approach is to create a VPC endpoint for S3 (Gateway type) and enable AWS CloudTrail to log S3 API calls. This works because a Gateway VPC endpoint provides private, direct connectivity from EC2 instances in a private subnet to S3 without traversing the internet or a NAT gateway, while CloudTrail captures the data plane API calls (like GetObject or PutObject) made to S3, logging them to a specified S3 bucket or CloudWatch Logs. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this question tests your ability to distinguish between network-level logging (VPC Flow Logs) and application-level logging (CloudTrail), a common trap where candidates confuse traffic logs with API call logs. Remember, Flow Logs show IP traffic, not S3 API actions—CloudTrail is the only service that records the specific API calls. Memory tip: "Flow for flows, Trail for trails"—VPC Flow Logs track network flows, CloudTrail tracks API trails.
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 has a VPC with a public subnet containing a NAT gateway and a private subnet with EC2 instances. The EC2 instances need to access an S3 bucket. The security team wants to log all S3 API calls made by the instances. Which approach should be used?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a VPC endpoint for S3 (Gateway type) and enable AWS CloudTrail to log S3 API calls
Option B is correct. VPC endpoint for S3 with bucket policies and CloudTrail can log API calls. Option A is wrong because Flow Logs capture network traffic, not API calls. Option C is wrong because a proxy would add complexity. Option D is wrong because CloudWatch alone does not log API calls.
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.
✗
Enable Amazon CloudWatch Logs on the instances to capture application logs
Why it's wrong here
Application logs may not capture all S3 API calls.
✗
Configure a proxy server in the public subnet and use it for S3 access
Why it's wrong here
Proxies can log but add complexity; CloudTrail is simpler.
✗
Enable VPC Flow Logs on the private subnet
Why it's wrong here
Flow Logs capture IP traffic, not S3 API calls.
✓
Create a VPC endpoint for S3 (Gateway type) and enable AWS CloudTrail to log S3 API calls
Why this is correct
CloudTrail logs API calls, and the VPC endpoint ensures traffic stays within AWS.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
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 a VPC endpoint for S3 (Gateway type) and enable AWS CloudTrail to log S3 API calls — Option B is correct. VPC endpoint for S3 with bucket policies and CloudTrail can log API calls. Option A is wrong because Flow Logs capture network traffic, not API calls. Option C is wrong because a proxy would add complexity. Option D is wrong because CloudWatch alone does not log API calls.
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.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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