The answer is that the ALB health check is too aggressive, causing tasks to be marked unhealthy during brief initialization or deployment. This is because the health check interval of 30 seconds combined with a threshold of 2 consecutive failures means a task can be removed from service in as little as 60 seconds, while the rolling update strategy with a minimum healthy percent of 50% and maximum of 200% can temporarily leave only one healthy task; if that single task is flagged unhealthy during its startup or a deployment cycle, the HealthyHostCount metric drops to zero, triggering intermittent 502 errors. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding of how ECS rolling updates interact with ALB health check timing—a common trap is to blame resource limits or AZ configuration when the real culprit is the health check sensitivity. Memory tip: think “60-second boot vs. 60-second kill”—if your health check can mark a task unhealthy faster than your task can become healthy, you’ll see 502s.
DOP-C02 Resilient Cloud Solutions Practice Question
This DOP-C02 practice question tests your understanding of resilient cloud solutions. 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 runs a production application on Amazon ECS with Fargate, fronted by an Application Load Balancer (ALB). The application experiences periodic latency spikes and occasional 502 errors. The ECS service is configured with a desired count of 2 tasks, and the ALB health check is set to /health with a 30-second interval and 2 consecutive failures threshold. The team uses CloudWatch Container Insights and has noticed that CPU and memory utilization of tasks remain below 50%. However, the ALB TargetGroup's HealthyHostCount metric occasionally drops to 0 for a few minutes before recovering. The deployment strategy is rolling update with a minimum healthy percent of 50% and maximum percent of 200%. The team recently updated the task definition to increase memory and CPU, but the issue persists. What is the MOST likely cause of the problem?
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.
Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The ALB health check is too aggressive, causing tasks to be marked unhealthy during brief initialization or deployment.
Option B is correct because the health check interval (30 seconds) and failure threshold (2) mean it takes up to 60 seconds to mark a task unhealthy. During deployments, the rolling update may temporarily have only 1 healthy task (minimum 50% of 2 = 1), and if that task becomes unhealthy, HealthyHostCount drops to 0. Option A is wrong because CPU and memory are below 50%, so resource limits are not the issue. Option C is wrong because a target group with 2 tasks and 2 AZs is fine; the problem is not AZ-specific. Option D is wrong because ECS service-linked role does not affect health checks.
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 role lacks permissions to register targets with the ALB.
Why it's wrong here
Permissions would cause persistent registration failures, not intermittent drops.
✓
The ALB health check is too aggressive, causing tasks to be marked unhealthy during brief initialization or deployment.
Why this is correct
Health check timing causes temporary loss of healthy targets during rolling updates.
Clue confirmation
The clue words "most likely", "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The ALB target group is configured with only one Availability Zone, causing loss of all targets when that AZ fails.
Why it's wrong here
The issue is not AZ failure but health check flapping.
✗
The task's CPU or memory limits are set too low, causing the container to be throttled.
Why it's wrong here
Metrics show low utilization, not throttling.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Trap categories for this question
Command / output trap
Metrics show low utilization, not throttling.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Identify which DOP-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Resilient Cloud Solutions — This question tests Resilient Cloud Solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The ALB health check is too aggressive, causing tasks to be marked unhealthy during brief initialization or deployment. — Option B is correct because the health check interval (30 seconds) and failure threshold (2) mean it takes up to 60 seconds to mark a task unhealthy. During deployments, the rolling update may temporarily have only 1 healthy task (minimum 50% of 2 = 1), and if that task becomes unhealthy, HealthyHostCount drops to 0. Option A is wrong because CPU and memory are below 50%, so resource limits are not the issue. Option C is wrong because a target group with 2 tasks and 2 AZs is fine; the problem is not AZ-specific. Option D is wrong because ECS service-linked role does not affect health checks.
What should I do if I get this DOP-C02 question wrong?
Identify which DOP-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Are there clue words in this question I should notice?
Yes — watch for: "most likely", "minimum / minimize". 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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