The answer is to create VPC Flow Logs in each account, specifying the central S3 bucket ARN as the destination, and configure the bucket policy to allow the flow logs service principal to write. This works because VPC Flow Logs natively support publishing directly to an S3 bucket in another account by ARN, and the bucket policy must explicitly grant the `delivery.logs.amazonaws.com` service principal the `s3:PutObject` permission—no IAM roles or cross-account users are needed. On the AWS Certified Security Specialty SCS-C02 exam, this tests your understanding of service principals versus IAM roles for cross-account delivery, and the common trap is confusing VPC Flow Logs with CloudTrail or assuming Kinesis Firehose is required. Remember: VPC Flow Logs use a service principal, not a user or role, so the bucket policy is the only access control needed. Memory tip: “Flow logs flow to S3 via service principal, not a principal you.”
SCS-C02 Security Logging and Monitoring Practice Question
This SCS-C02 practice question tests your understanding of security logging and monitoring. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 multiple AWS accounts and wants to centrally aggregate VPC Flow Logs from all accounts into a single S3 bucket in the logging account. What is the MOST secure way to configure cross-account delivery?
Use AWS CloudTrail to log flow logs and deliver to the central bucket.
Why wrong: CloudTrail does not handle VPC Flow Logs.
B
Create VPC Flow Logs in each account, specifying the central S3 bucket ARN as the destination, and configure the bucket policy to allow the flow logs service principal to write.
This is the standard cross-account flow log delivery method.
C
Share the central bucket's access key with each account to write directly.
Why wrong: Sharing access keys is insecure.
D
Use Amazon Kinesis Data Firehose to stream flow logs from each account to the central S3 bucket.
Why wrong: Kinesis Data Firehose is not directly integrated with VPC Flow Logs.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create VPC Flow Logs in each account, specifying the central S3 bucket ARN as the destination, and configure the bucket policy to allow the flow logs service principal to write.
Option A is correct because VPC Flow Logs can be published to a central S3 bucket by specifying the bucket ARN in the flow log creation, and the bucket policy must grant the flow logs service principal (delivery.logs.amazonaws.com) permission to write objects. Option B is wrong because CloudTrail is for API logging, not VPC Flow Logs. Option C is wrong because Kinesis Data Firehose is not directly supported for VPC Flow Logs delivery. Option D is wrong because sharing the bucket access key is insecure.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 AWS CloudTrail to log flow logs and deliver to the central bucket.
Why it's wrong here
CloudTrail does not handle VPC Flow Logs.
✓
Create VPC Flow Logs in each account, specifying the central S3 bucket ARN as the destination, and configure the bucket policy to allow the flow logs service principal to write.
Why this is correct
This is the standard cross-account flow log delivery method.
Related concept
Static NAT maps one inside address to one outside address.
✗
Share the central bucket's access key with each account to write directly.
Why it's wrong here
Sharing access keys is insecure.
✗
Use Amazon Kinesis Data Firehose to stream flow logs from each account to the central S3 bucket.
Why it's wrong here
Kinesis Data Firehose is not directly integrated with VPC Flow Logs.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SCS-C02 NAT questions on configuration and troubleshooting.
Security Logging and Monitoring — This question tests Security Logging and Monitoring — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Create VPC Flow Logs in each account, specifying the central S3 bucket ARN as the destination, and configure the bucket policy to allow the flow logs service principal to write. — Option A is correct because VPC Flow Logs can be published to a central S3 bucket by specifying the bucket ARN in the flow log creation, and the bucket policy must grant the flow logs service principal (delivery.logs.amazonaws.com) permission to write objects. Option B is wrong because CloudTrail is for API logging, not VPC Flow Logs. Option C is wrong because Kinesis Data Firehose is not directly supported for VPC Flow Logs delivery. Option D is wrong because sharing the bucket access key is insecure.
What should I do if I get this SCS-C02 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SCS-C02 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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