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Troubleshooting and Optimization →mediumMultiple ChoiceObjective-mapped

DVA-C02 Troubleshooting and Optimization Practice Question

This DVA-C02 practice question tests your understanding of troubleshooting and optimization. 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 developer is troubleshooting a Lambda function that processes S3 events. The function runs successfully in the AWS Management Console test but fails when triggered by actual S3 PUT events. The error logs show 'AccessDenied' when attempting to read the object from S3. 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.

A
The S3 bucket has versioning enabled and the event does not include the version ID.
Why wrong: Versioning does not prevent access; the function can read the latest version without a version ID.
B
The Lambda execution role lacks 's3:GetObject' permission for the bucket.
The Lambda role must have permission to read the object from S3.
C
The S3 bucket policy does not grant 's3:GetObject' to the Lambda service principal.
Why wrong: The bucket policy should grant access to the Lambda execution role, not the service principal.
D
The Lambda function is not in the same VPC as the S3 bucket.
Why wrong: S3 is a regional service; VPC configuration is not required for S3 access.

Full breakdown with real-world context →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

The Lambda execution role lacks 's3:GetObject' permission for the bucket.

The Lambda function's execution role must have 's3:GetObject' permission to read the object from S3. When the function is triggered by an actual S3 event, it uses this role. The console test may use a different role or bypass permissions, masking the issue. Option B correctly identifies that the execution role lacks the required permission. Option A is incorrect because versioning does not cause 'AccessDenied' for reads. Option C is incorrect because the bucket policy granting access to the Lambda service principal is not required; the execution role handles permissions. Option D is incorrect because Lambda and S3 do not need to be in the same VPC.

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 has versioning enabled and the event does not include the version ID.
Why it's wrong here
Versioning does not prevent access; the function can read the latest version without a version ID.
✓
The Lambda execution role lacks 's3:GetObject' permission for the bucket.
Why this is correct
The Lambda role must have permission to read the object from S3.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
✗
The S3 bucket policy does not grant 's3:GetObject' to the Lambda service principal.
Why it's wrong here
The bucket policy should grant access to the Lambda execution role, not the service principal.
✗
The Lambda function is not in the same VPC as the S3 bucket.
Why it's wrong here
S3 is a regional service; VPC configuration is not required for S3 access.

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.

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.

Quick reference

AWS S3 Storage Class Comparison

Storage Class	Min Duration	Retrieval	Use Case
S3 Standard	None	Immediate	Frequently accessed data
S3 Standard-IA	30 days	Immediate	Infrequent access, rapid retrieval
S3 One Zone-IA	30 days	Immediate	Non-critical infrequent data
S3 Intelligent-Tiering	None	Immediate–hours	Unknown or changing access patterns
S3 Glacier Instant	90 days	Milliseconds	Archive with instant retrieval
S3 Glacier Flexible	90 days	Minutes–hours	Archive, flexible retrieval
S3 Glacier Deep Archive	180 days	Hours	Long-term compliance archive

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 DVA-C02 subnetting questions on CIDR, address ranges, and subnet selection.

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FAQ

Questions learners often ask

What does this DVA-C02 question test?

Troubleshooting and Optimization — This question tests Troubleshooting and Optimization — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: The Lambda execution role lacks 's3:GetObject' permission for the bucket. — The Lambda function's execution role must have 's3:GetObject' permission to read the object from S3. When the function is triggered by an actual S3 event, it uses this role. The console test may use a different role or bypass permissions, masking the issue. Option B correctly identifies that the execution role lacks the required permission. Option A is incorrect because versioning does not cause 'AccessDenied' for reads. Option C is incorrect because the bucket policy granting access to the Lambda service principal is not required; the execution role handles permissions. Option D is incorrect because Lambda and S3 do not need to be in the same VPC.

What should I do if I get this DVA-C02 question wrong?

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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