- A
The Auto Scaling group's cooldown period prevents new instances from being added quickly enough during rapid traffic spikes
After a scaling activity, the cooldown period (300s by default) pauses further scaling, causing delays that can result in all instances becoming unhealthy and returning 503 errors.
- B
The ALB's idle timeout is set too low, causing dropped connections
Why wrong: Idle timeout affects persistent connections but does not cause 503 errors due to insufficient healthy hosts.
- C
The Auto Scaling group's maximum capacity of 10 is insufficient
Why wrong: With 10 instances, the group should be able to handle high traffic; the issue is more about the speed of scaling, not the maximum.
- D
The health check grace period is preventing instances from being marked healthy
Why wrong: Grace period gives new instances time to start; it would cause a delay in recognizing health, but not the intermittent loss of all healthy hosts after a scaling event.
Quick Answer
The answer is the Auto Scaling group's cooldown period preventing new instances from being added quickly enough during rapid traffic spikes. This occurs because a simple scaling policy enforces a default 300-second cooldown after each scaling action, which blocks further instance launches even when newly added instances are still initializing and the healthy host count drops to zero. During peak hours, the ALB has no healthy targets to route traffic to, resulting in HTTP 503 errors despite the request count remaining below limits. On the AWS Certified Developer Associate DVA-C02 exam, this scenario tests your understanding of how simple scaling policies interact with cooldown periods, a common trap where developers assume adding instances instantly resolves capacity issues. The key distinction is that cooldown pauses all scaling activities, not just the triggering metric evaluation. Memory tip: think "Cooldown = Cold Shoulder" — the Auto Scaling group ignores new demand until the timer expires, leaving the ALB with no warm targets.
DVA-C02 Troubleshooting and Optimization Practice Question
This DVA-C02 practice question tests your understanding of troubleshooting and optimization. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 web application runs on Amazon EC2 instances behind an Application Load Balancer (ALB). During peak hours, users report receiving HTTP 503 (Service Unavailable) errors. The developer checks Amazon CloudWatch metrics and finds that the ALB's request count is high but below the limit, and the target group's healthy host count drops to zero intermittently. The Auto Scaling group for the instances is configured with a minimum of 2, maximum of 10, and a simple scaling policy to add 2 instances when CPU utilization exceeds 70% for 5 consecutive minutes. What is the most likely cause of the 503 errors?
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 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 Auto Scaling group's cooldown period prevents new instances from being added quickly enough during rapid traffic spikes
The 503 errors occur because the simple scaling policy has a cooldown period (default 300 seconds) that prevents the Auto Scaling group from launching new instances during rapid traffic spikes. When CPU exceeds 70% for 5 minutes, the policy adds 2 instances, but the cooldown blocks further scaling actions until it expires, even if the newly launched instances are still initializing and the healthy host count drops to zero. This mismatch between traffic demand and scaling responsiveness causes the ALB to have no healthy targets, resulting in 503 errors.
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 Auto Scaling group's cooldown period prevents new instances from being added quickly enough during rapid traffic spikes
Why this is correct
After a scaling activity, the cooldown period (300s by default) pauses further scaling, causing delays that can result in all instances becoming unhealthy and returning 503 errors.
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's idle timeout is set too low, causing dropped connections
Why it's wrong here
Idle timeout affects persistent connections but does not cause 503 errors due to insufficient healthy hosts.
- ✗
The Auto Scaling group's maximum capacity of 10 is insufficient
Why it's wrong here
With 10 instances, the group should be able to handle high traffic; the issue is more about the speed of scaling, not the maximum.
- ✗
The health check grace period is preventing instances from being marked healthy
Why it's wrong here
Grace period gives new instances time to start; it would cause a delay in recognizing health, but not the intermittent loss of all healthy hosts after a scaling event.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume 503 errors are always due to capacity limits (Option C) or misconfigured health checks (Option D), but the real issue is the cooldown period's impact on scaling responsiveness during rapid traffic spikes.
Detailed technical explanation
How to think about this question
Under the hood, the simple scaling policy's cooldown period prevents the Auto Scaling group from executing additional scaling activities until the cooldown expires, even if the alarm condition persists. This is designed to avoid flapping, but during rapid traffic spikes, it can lead to a situation where the group cannot scale fast enough to replace unhealthy instances, causing the ALB's target group to have zero healthy hosts. In contrast, step scaling or target tracking policies can scale more aggressively without cooldown limitations, making them better suited for variable traffic patterns.
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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Troubleshooting and Optimization — study guide chapter
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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 — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The Auto Scaling group's cooldown period prevents new instances from being added quickly enough during rapid traffic spikes — The 503 errors occur because the simple scaling policy has a cooldown period (default 300 seconds) that prevents the Auto Scaling group from launching new instances during rapid traffic spikes. When CPU exceeds 70% for 5 minutes, the policy adds 2 instances, but the cooldown blocks further scaling actions until it expires, even if the newly launched instances are still initializing and the healthy host count drops to zero. This mismatch between traffic demand and scaling responsiveness causes the ALB to have no healthy targets, resulting in 503 errors.
What should I do if I get this DVA-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", "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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Last reviewed: Jun 11, 2026
This DVA-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DVA-C02 exam.
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