The answer is that the VPC does not have a VPC endpoint for S3. This is the most likely cause because the EC2 instance resides in a private subnet without an internet gateway, meaning it has no public route to reach S3 over the internet. To fix EC2 instance in private subnet unable to access S3, you must establish private connectivity via a VPC endpoint—either a Gateway Endpoint for S3 or an Interface Endpoint—which allows traffic to stay within the AWS network. On the AWS Certified Data Engineer Associate DEA-C01 exam, this scenario tests your understanding of VPC networking fundamentals and the distinction between public and private subnet access patterns. A common trap is assuming an internet gateway is always required, but the correct solution is a VPC endpoint. Memory tip: No IGW? No problem—just point to the endpoint.
DEA-C01 Data Operations and Support Practice Question
This DEA-C01 practice question tests your understanding of data operations and support. 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.
Exhibit
Refer to the exhibit.
2024-03-15 10:23:45,678 ERROR [main] com.amazonaws.services.s3.AmazonS3Client : Unable to execute HTTP request: Connect to my-bucket.s3.us-west-2.amazonaws.com:443 [my-bucket.s3.us-west-2.amazonaws.com/10.0.0.1] failed: connect timed out
Refer to the exhibit. A data engineer sees this error log from an Amazon EC2 instance that is trying to access an S3 bucket in the us-west-2 region. The EC2 instance is in a VPC with a private subnet and no internet gateway. What is the MOST likely cause of this error?
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.
Refer to the exhibit.
2024-03-15 10:23:45,678 ERROR [main] com.amazonaws.services.s3.AmazonS3Client : Unable to execute HTTP request: Connect to my-bucket.s3.us-west-2.amazonaws.com:443 [my-bucket.s3.us-west-2.amazonaws.com/10.0.0.1] failed: connect timed out
A
The S3 bucket is in a different region than us-west-2.
Why wrong: The error shows us-west-2 endpoint.
B
The VPC does not have a VPC endpoint for S3.
Private subnet needs VPC endpoint to access S3.
C
The S3 bucket does not exist.
Why wrong: DNS resolves, so bucket exists.
D
The IAM role attached to the EC2 instance does not have s3:GetObject permission.
Why wrong: Permission errors return 403, not timeout.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The VPC does not have a VPC endpoint for S3.
Option D is correct. The EC2 instance is in a private subnet without internet gateway, so it cannot reach S3 over the internet. A VPC endpoint (Gateway or Interface) is needed for private connectivity. Option A is incorrect because the bucket exists (DNS resolves). Option B is incorrect because the error is a connection timeout, not a 403. Option C is incorrect because there is no indication of an incorrect region.
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 S3 bucket is in a different region than us-west-2.
Why it's wrong here
The error shows us-west-2 endpoint.
✓
The VPC does not have a VPC endpoint for S3.
Why this is correct
Private subnet needs VPC endpoint to access S3.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The IAM role attached to the EC2 instance does not have s3:GetObject permission.
Why it's wrong here
Permission errors return 403, not timeout.
Common exam traps
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
The error shows us-west-2 endpoint.
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 DEA-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Data Operations and Support — This question tests Data Operations and Support — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The VPC does not have a VPC endpoint for S3. — Option D is correct. The EC2 instance is in a private subnet without internet gateway, so it cannot reach S3 over the internet. A VPC endpoint (Gateway or Interface) is needed for private connectivity. Option A is incorrect because the bucket exists (DNS resolves). Option B is incorrect because the error is a connection timeout, not a 403. Option C is incorrect because there is no indication of an incorrect region.
What should I do if I get this DEA-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 DEA-C01 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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