The answer is to configure the KMS key policy to allow the log-producing accounts to use the key, and the S3 bucket policy to allow those accounts to write. This is correct because cross-account VPC flow logs with KMS encryption require a two-layer permission model: the KMS key policy must explicitly grant the producing accounts the kms:Encrypt and kms:GenerateDataKey permissions, while the S3 bucket policy must grant s3:PutObject access to those same accounts, ensuring the logs are encrypted at rest with a centralized customer-managed key. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of how IAM, KMS, and S3 policies interact across accounts—a common trap is assuming the S3 bucket policy alone can handle encryption permissions, but KMS cross-account access always requires a key policy. Memory tip: think “Key policy for crypto, Bucket policy for write”—two policies, one centralized key.
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 multi-account architecture. They need to centralize VPC flow logs from all accounts into a single Amazon S3 bucket in the security account. The logs must be encrypted at rest using a customer-managed KMS key in the security account. Which combination of steps is required?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure the KMS key policy to allow the log-producing accounts to use the key, and the S3 bucket policy to allow those accounts to write.
Option D is correct because cross-account KMS access requires a KMS key policy that grants the log-producing accounts permission to use the key, and the S3 bucket policy must allow cross-account writes. Option A is wrong because using a single KMS key with cross-account access requires key policy. Option B is wrong because a CMK in each account would not be centralized. Option C is wrong because S3 bucket policy alone does not handle encryption permissions.
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.
✗
Configure the S3 bucket policy to allow the log accounts to write; encryption is automatic with SSE-S3.
Why it's wrong here
Requires customer-managed KMS key, not SSE-S3.
✗
Create a KMS key in each account and configure the S3 bucket to use each key.
Why it's wrong here
Not centralized; each account uses its own key.
✓
Configure the KMS key policy to allow the log-producing accounts to use the key, and the S3 bucket policy to allow those accounts to write.
Static NAT maps one inside address to one outside address.
✗
Create a KMS key in the security account with no key policy changes; use bucket policies to allow cross-account writes.
Why it's wrong here
KMS key needs cross-account permissions in key policy.
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 ANS-C01 NAT questions on configuration and troubleshooting.
Network Security, Compliance and Governance — This question tests Network Security, Compliance and Governance — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Configure the KMS key policy to allow the log-producing accounts to use the key, and the S3 bucket policy to allow those accounts to write. — Option D is correct because cross-account KMS access requires a KMS key policy that grants the log-producing accounts permission to use the key, and the S3 bucket policy must allow cross-account writes. Option A is wrong because using a single KMS key with cross-account access requires key policy. Option B is wrong because a CMK in each account would not be centralized. Option C is wrong because S3 bucket policy alone does not handle encryption permissions.
What should I do if I get this ANS-C01 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 ANS-C01 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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