DOP-C02 Incident and Event Response Practice Question
This DOP-C02 practice question tests your understanding of incident and event response. 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.
An application running on Amazon ECS (Fargate) experiences intermittent HTTP 503 errors. The application uses an Application Load Balancer. The ECS service has a desired count of 2. CPU and memory utilization are below 50%. 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 target group health check threshold is set too low.
Intermittent HTTP 503 errors from an Application Load Balancer (ALB) typically indicate that the target group health checks are failing, causing the ALB to stop routing traffic to the affected tasks. With a desired count of 2 and low CPU/memory utilization, the most likely cause is a health check threshold set too low (e.g., a low unhealthy threshold count), which makes the ALB prematurely mark tasks as unhealthy during transient issues, leading to no healthy targets and 503 responses. This aligns with the symptom of intermittent errors, as tasks may briefly fail a health check but recover quickly, yet the low threshold causes them to be deregistered.
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 ECS service Auto Scaling is too aggressive.
Why it's wrong here
Auto Scaling is not triggered because CPU/memory are below thresholds.
✓
The target group health check threshold is set too low.
Why this is correct
A low threshold may mark healthy instances as unhealthy, causing 503 errors.
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.
✗
The ALB listener rule is misconfigured.
Why it's wrong here
Misconfigured listener would cause consistent errors, not intermittent.
✗
The task definition has an incorrect memory hard limit.
Why it's wrong here
Memory utilization is below 50%, so hard limit is not exceeded.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often attribute 503 errors to resource exhaustion (CPU/memory) or scaling issues, but the question explicitly states low utilization, forcing you to focus on health check configuration as the root cause of intermittent availability.
Detailed technical explanation
How to think about this question
The ALB health check mechanism uses configurable thresholds: healthy_threshold_count (default 5) and unhealthy_threshold_count (default 2). If the unhealthy threshold is set to 1, a single failed health check (e.g., due to a brief network glitch or slow response) immediately marks the target as unhealthy, and the ALB stops sending traffic to it. With only 2 tasks, if both are briefly marked unhealthy, the ALB has no healthy targets and returns HTTP 503. This is a common misconfiguration in production where operators lower thresholds for faster recovery but inadvertently cause flapping.
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.
Incident and Event Response — This question tests Incident and Event Response — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The target group health check threshold is set too low. — Intermittent HTTP 503 errors from an Application Load Balancer (ALB) typically indicate that the target group health checks are failing, causing the ALB to stop routing traffic to the affected tasks. With a desired count of 2 and low CPU/memory utilization, the most likely cause is a health check threshold set too low (e.g., a low unhealthy threshold count), which makes the ALB prematurely mark tasks as unhealthy during transient issues, leading to no healthy targets and 503 responses. This aligns with the symptom of intermittent errors, as tasks may briefly fail a health check but recover quickly, yet the low threshold causes them to be deregistered.
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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Question Discussion
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