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Question 351 of 1,616

Troubleshooting and Optimization →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the application is not handling the SIGTERM signal from ECS, causing it to terminate abruptly while the ALB still routes traffic to it. This is the most likely cause of the 502 errors because during a rolling update, ECS sends a SIGTERM to the Fargate task to initiate a graceful shutdown; if the application ignores this signal and dies immediately, the task becomes unresponsive before the ALB’s connection draining can complete, leaving the load balancer to route requests to a dead target. On the AWS Certified Developer Associate DVA-C02 exam, this scenario tests your understanding of how container lifecycle hooks interact with load balancer health checks and deployment circuit breakers—a common trap is assuming connection draining alone prevents 502s, but it only works if the task signals its deregistration. Remember the memory tip: “SIGTERM is a polite request, not a kill command—ignore it, and your ALB will serve 502s.”

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.

An application running on Amazon ECS (Fargate) uses an Application Load Balancer (ALB) with connection draining enabled. The application is experiencing intermittent 502 (Bad Gateway) errors during rolling updates of the ECS service. The developer notices that the ALB is routing requests to tasks that are in the 'Draining' state. The ECS service is configured with a deployment circuit breaker that automatically rolls back a failed deployment. What is the most likely cause of the 502 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.

Question 1hardmultiple choice

Review the full routing breakdown →

A
The ALB's idle timeout is too short, causing connections to be dropped before the application responds.
Why wrong: An idle timeout that is too short would cause 504 errors, not 502. Also, the issue is specifically during rolling updates, not during steady state.
B
The ALB's connection draining timeout is set to 0 seconds, causing connections to be dropped immediately when deregistering targets.
Why wrong: A connection draining timeout of 0 would immediately stop new connections to draining targets, but existing connections would still be allowed to complete. It would not cause 502 errors; it might cause 504 if connections are not completed in time. More importantly, the ALB's connection draining is separate from ECS task draining.
C
The ECS deployment circuit breaker is incorrectly configured to roll back on health check failures.
Why wrong: The circuit breaker rolls back a failed deployment, but it does not cause 502 errors during the update. The errors occur before the rollback is triggered.
D
The application is not handling the SIGTERM signal from ECS, causing it to terminate abruptly while the ALB still routes traffic to it.
When ECS stops a task, it sends a SIGTERM signal to allow the application to gracefully shut down. If the application does not catch this signal and stop accepting new connections or complete in-flight requests before exiting, the ALB may still send traffic to the task after it stops, resulting in 502 errors. This is a common issue during rolling updates.

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 application is not handling the SIGTERM signal from ECS, causing it to terminate abruptly while the ALB still routes traffic to it.

Option D is correct because when ECS sends a SIGTERM signal to a Fargate task during a rolling update, the task is expected to gracefully shut down. If the application does not handle SIGTERM, it terminates immediately, but the ALB may still have the task registered as a target and continue routing requests to it. Since the task is already dead or unresponsive, the ALB receives no valid HTTP response and returns a 502 Bad Gateway error. Connection draining is enabled, but it only works if the task signals the ALB that it is deregistering; without proper SIGTERM handling, the task dies before the draining process completes.

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 ALB's idle timeout is too short, causing connections to be dropped before the application responds.
Why it's wrong here
An idle timeout that is too short would cause 504 errors, not 502. Also, the issue is specifically during rolling updates, not during steady state.
✗
The ALB's connection draining timeout is set to 0 seconds, causing connections to be dropped immediately when deregistering targets.
Why it's wrong here
A connection draining timeout of 0 would immediately stop new connections to draining targets, but existing connections would still be allowed to complete. It would not cause 502 errors; it might cause 504 if connections are not completed in time. More importantly, the ALB's connection draining is separate from ECS task draining.
✗
The ECS deployment circuit breaker is incorrectly configured to roll back on health check failures.
Why it's wrong here
The circuit breaker rolls back a failed deployment, but it does not cause 502 errors during the update. The errors occur before the rollback is triggered.
✓
The application is not handling the SIGTERM signal from ECS, causing it to terminate abruptly while the ALB still routes traffic to it.
Why this is correct
When ECS stops a task, it sends a SIGTERM signal to allow the application to gracefully shut down. If the application does not catch this signal and stop accepting new connections or complete in-flight requests before exiting, the ALB may still send traffic to the task after it stops, resulting in 502 errors. This is a common issue during rolling updates.
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 assume connection draining is a silver bullet that prevents all errors during rolling updates, but they overlook that the application must handle SIGTERM to allow the draining process to work as intended.

Detailed technical explanation

How to think about this question

When ECS sends a SIGTERM to a Fargate task, the task has a default 30-second grace period (configurable via `stopTimeout`) to shut down gracefully. If the application does not trap SIGTERM, the Linux kernel kills the process immediately, but the ECS agent may not have time to deregister the task from the ALB target group. The ALB continues to route requests to the deregistering target until the connection draining timeout expires, but since the task is already dead, the ALB receives a TCP RST or no response, resulting in a 502. In contrast, a well-behaved application would catch SIGTERM, stop accepting new requests, finish in-flight requests, and then exit, allowing the ALB to drain connections cleanly.

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 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 application is not handling the SIGTERM signal from ECS, causing it to terminate abruptly while the ALB still routes traffic to it. — Option D is correct because when ECS sends a SIGTERM signal to a Fargate task during a rolling update, the task is expected to gracefully shut down. If the application does not handle SIGTERM, it terminates immediately, but the ALB may still have the task registered as a target and continue routing requests to it. Since the task is already dead or unresponsive, the ALB receives no valid HTTP response and returns a 502 Bad Gateway error. Connection draining is enabled, but it only works if the task signals the ALB that it is deregistering; without proper SIGTERM handling, the task dies before the draining process completes.

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". 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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