The answer is to add a condition in the KMS key policy using 'aws:SourceVpc' to restrict usage to the VPC. This works because KMS key policies support the global condition key 'aws:SourceVpc', which evaluates the origin of the API request against the VPC ID you specify, effectively blocking any KMS operations that originate from outside that VPC. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this concept tests your understanding of how to combine resource-based policies with network-level controls, and it often appears as a distractor where candidates mistakenly try to use S3 bucket policies or IAM policies—both of which cannot enforce VPC restrictions on KMS actions. A common trap is confusing network ACLs, which control IP traffic at the subnet level, with the API-level control provided by KMS key policies. Remember the memory tip: "Key policy, VPC key" — the restriction lives in the key policy itself, not in the network layer.
SOA-C02 Security and Compliance Practice Question
This SOA-C02 practice question tests your understanding of security and compliance. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 uses AWS Key Management Service (KMS) to encrypt data in Amazon S3. They want to ensure that the KMS key can only be used from within a specific VPC. How can this be accomplished?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add a condition in the KMS key policy using 'aws:SourceVpc' to restrict usage to the VPC.
Option D is correct because a KMS key policy can use the 'aws:SourceVpc' condition to restrict usage to requests originating from a specific VPC. Option A is wrong because S3 bucket policies cannot restrict KMS key usage. Option B is wrong because IAM policies cannot restrict based on VPC for KMS actions. Option C is wrong because network ACLs control network traffic, not KMS API calls.
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.
✗
Add a condition in the S3 bucket policy to allow only requests from the VPC.
Why it's wrong here
S3 bucket policy does not control KMS key usage.
✓
Add a condition in the KMS key policy using 'aws:SourceVpc' to restrict usage to the VPC.
Static NAT maps one inside address to one outside address.
✗
Use an IAM policy with a condition that requires the request to come from the VPC.
Why it's wrong here
IAM policies cannot restrict KMS based on VPC.
✗
Configure a network ACL that blocks all traffic to KMS except from the VPC.
Why it's wrong here
NACLs control network traffic, not API calls.
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 SOA-C02 NAT questions on configuration and troubleshooting.
Security and Compliance — This question tests Security and Compliance — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Add a condition in the KMS key policy using 'aws:SourceVpc' to restrict usage to the VPC. — Option D is correct because a KMS key policy can use the 'aws:SourceVpc' condition to restrict usage to requests originating from a specific VPC. Option A is wrong because S3 bucket policies cannot restrict KMS key usage. Option B is wrong because IAM policies cannot restrict based on VPC for KMS actions. Option C is wrong because network ACLs control network traffic, not KMS API calls.
What should I do if I get this SOA-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 SOA-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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Question Discussion
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