The answer is that the condition key aws:SourceIp evaluates the private IP of the EC2 instance, but S3 traffic from an EC2 instance in a VPC traverses the internet and is seen by S3 as originating from the instance’s public IP, causing the condition to fail. This happens because the IAM policy with a source IP condition checks the IP address at the S3 endpoint, and when an EC2 instance accesses S3 without a VPC endpoint, the request’s source IP is the public IP assigned to the instance, not its private RFC 1918 address. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of how network paths affect IAM condition evaluation—a common trap is assuming private IPs are visible to AWS services outside the VPC. Remember, for S3 access from EC2, the source IP seen by S3 is always the public IP unless you use a VPC gateway endpoint, which bypasses the internet entirely. A useful memory tip: “Private IPs stay inside the VPC; S3 sees the public you.”
SAP-C02 Practice Question: Accelerate Workload Migration and Modernization
This SAP-C02 practice question tests your understanding of accelerate workload migration and modernization. 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.
Refer to the exhibit. A company has attached this IAM policy to an IAM role used by an application running on an EC2 instance in a VPC with CIDR 10.0.0.0/16. The application is unable to read objects from the S3 bucket. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The condition key aws:SourceIp uses the private IP of the instance, but S3 sees the public IP.
Option D is correct because the condition checks the source IP of the request, but EC2 instances use public IPs when accessing S3, so the private IP condition fails. Option A is wrong because the policy allows GetObject. Option B is wrong because S3 does not require a role for bucket access. Option C is wrong because the bucket policy is not shown.
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.
✗
The EC2 instance does not have an IAM instance profile.
Why it's wrong here
The role is attached, so it does.
✗
The policy does not allow the s3:ListBucket action.
Why it's wrong here
The application is reading objects, not listing.
✓
The condition key aws:SourceIp uses the private IP of the instance, but S3 sees the public IP.
Why this is correct
The condition fails because traffic to S3 originates from the public IP.
Clue confirmation
The clue word "most likely" 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.
Trap categories for this question
Command / output trap
No bucket policy is shown.
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 SAP-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Accelerate Workload Migration and Modernization — This question tests Accelerate Workload Migration and Modernization — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The condition key aws:SourceIp uses the private IP of the instance, but S3 sees the public IP. — Option D is correct because the condition checks the source IP of the request, but EC2 instances use public IPs when accessing S3, so the private IP condition fails. Option A is wrong because the policy allows GetObject. Option B is wrong because S3 does not require a role for bucket access. Option C is wrong because the bucket policy is not shown.
What should I do if I get this SAP-C02 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 SAP-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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