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Monitoring and Logging →hardMultiple ChoiceObjective-mapped

DOP-C02 Monitoring and Logging Practice Question

This DOP-C02 practice question tests your understanding of monitoring and logging. 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 is using AWS X-Ray to trace requests through a microservices application. Some traces are incomplete, showing only the root segment without any subsegments. The application uses the X-Ray SDK for Java. 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 application is missing the x-amzn-trace-id header in incoming requests.
Why wrong: Missing the x-amzn-trace-id header would not cause subsegments to be omitted; it would affect trace propagation across services but not the generation of subsegments within a single service.
B
The segment document size exceeds the maximum allowed size.
Why wrong: If the segment document exceeds the maximum size, the SDK would likely fail to send the segment, resulting in an error or dropped trace entirely, not a trace with only a root segment.
C
The X-Ray daemon is not running on the EC2 instances.
Why wrong: The X-Ray SDK on EC2 instances sends trace segments to the X-Ray daemon, which then forwards them to the X-Ray API. If the daemon is not running, the SDK cannot send any segments, resulting in no traces at all. However, the issue here is incomplete traces with only root segments, which is more consistent with a low sampling rate rather than a missing daemon. Therefore, option C is not the most likely cause.
D
The sampling rate is set to a low value, causing many requests to be dropped.
A low sampling rate causes the SDK to sample only a fraction of requests. When a request is not sampled, only the root segment is recorded without subsegments, leading to incomplete traces.

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 sampling rate is set to a low value, causing many requests to be dropped.

Option D is correct because a low sampling rate in the X-Ray SDK causes the SDK to drop many requests before they are sent to the daemon. When the sampling rate is too low, the SDK may decide not to record subsegments for a given request, resulting in traces that contain only the root segment without any subsegments. This is a common misconfiguration where the sampling decision is made at the segment level, and subsegments are only generated if the segment is sampled in. Option A is incorrect because the x-amzn-trace-id header is not required for tracing; the SDK can generate its own trace ID. Option B is incorrect because segment documents that exceed the maximum size are rejected by the API, not silently ignored. Option C is incorrect because the X-Ray daemon is required for the SDK to send traces to the X-Ray API. If the daemon is not running, the SDK cannot send segments, resulting in no traces at all, not incomplete traces with only root segments. The incomplete traces described are typically due to sampling issues.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

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 application is missing the x-amzn-trace-id header in incoming requests.
Why it's wrong here
Missing the x-amzn-trace-id header would not cause subsegments to be omitted; it would affect trace propagation across services but not the generation of subsegments within a single service.
✗
The segment document size exceeds the maximum allowed size.
Why it's wrong here
If the segment document exceeds the maximum size, the SDK would likely fail to send the segment, resulting in an error or dropped trace entirely, not a trace with only a root segment.
✗
The X-Ray daemon is not running on the EC2 instances.
Why it's wrong here
The X-Ray SDK on EC2 instances sends trace segments to the X-Ray daemon, which then forwards them to the X-Ray API. If the daemon is not running, the SDK cannot send any segments, resulting in no traces at all. However, the issue here is incomplete traces with only root segments, which is more consistent with a low sampling rate rather than a missing daemon. Therefore, option C is not the most likely cause.
✓
The sampling rate is set to a low value, causing many requests to be dropped.
Why this is correct
A low sampling rate causes the SDK to sample only a fraction of requests. When a request is not sampled, only the root segment is recorded without subsegments, leading to incomplete traces.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often confuse a low sampling rate with the X-Ray daemon being down, but a missing daemon would cause a complete absence of traces, whereas a low sampling rate produces partial traces with only root segments.

Detailed technical explanation

How to think about this question

The X-Ray SDK uses a reservoir and rate-based sampling algorithm defined in the sampling rules. When the sampling rate is set too low (e.g., 1% or less), the SDK may sample the root segment but then decide not to record subsegments due to downstream sampling decisions or because the segment is marked as 'not sampled' after the initial decision. In a real-world scenario, this often happens when developers set a fixed sampling rate without understanding that subsegments inherit the sampling decision from the parent segment, leading to incomplete traces that are hard to debug.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.

TExam Day Tips

Watch for words such as best, first, most likely and least administrative effort.
Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this DOP-C02 question test?

Monitoring and Logging — This question tests Monitoring and Logging — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The sampling rate is set to a low value, causing many requests to be dropped. — Option D is correct because a low sampling rate in the X-Ray SDK causes the SDK to drop many requests before they are sent to the daemon. When the sampling rate is too low, the SDK may decide not to record subsegments for a given request, resulting in traces that contain only the root segment without any subsegments. This is a common misconfiguration where the sampling decision is made at the segment level, and subsegments are only generated if the segment is sampled in. Option A is incorrect because the x-amzn-trace-id header is not required for tracing; the SDK can generate its own trace ID. Option B is incorrect because segment documents that exceed the maximum size are rejected by the API, not silently ignored. Option C is incorrect because the X-Ray daemon is required for the SDK to send traces to the X-Ray API. If the daemon is not running, the SDK cannot send segments, resulting in no traces at all, not incomplete traces with only root segments. The incomplete traces described are typically due to sampling issues.

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

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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?

Read the scenario before looking for a memorised answer.

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