Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
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?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Distractor review
The ALB's idle timeout is too short, causing connections to be dropped before the application responds.
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
Distractor review
The ALB's connection draining timeout is set to 0 seconds, causing connections to be dropped immediately when deregistering targets.
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
Distractor review
The ECS deployment circuit breaker is incorrectly configured to roll back on health check failures.
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
Best answer
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.
Common exam trap
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Technical deep dive
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
- Static NAT maps one inside address to one outside address.
- PAT allows many inside hosts to share one public address using ports.
- Inside local and inside global describe the private and translated addresses.
- NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
- Identify inside and outside interfaces first.
- Check whether the scenario needs static NAT, dynamic NAT or PAT.
- Do not confuse NAT matching ACLs with normal packet-filtering intent.
Related practice questions
Related DVA-C02 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A developer is building a REST API using Amazon API Gateway that will serve static content from an Amazon S3 bucket. The API should cache responses for frequently accessed objects to reduce latency. Which API Gateway feature should the developer enable?
Question 2
A developer is running a web application on multiple Amazon EC2 instances behind an Application Load Balancer (ALB). The application needs to store user session state that must be available across all instances. The session data is small and temporary but must survive individual instance failures. Which AWS service should the developer use to store this session state?
Question 3
A developer has an AWS Lambda function that processes messages from an Amazon SQS standard queue. The function is idempotent and currently has a batch size of 10. The developer wants to increase throughput and increases the batch size to 100. After the change, CloudWatch metrics show a significant increase in throttles and the queue backlog is growing. The function's reserved concurrency is set to 10. What is the most effective action to resolve the throttling and improve throughput?
Question 4
A developer is managing an application running on Amazon EC2 instances behind an Application Load Balancer. Users report that the application becomes unresponsive after several hours, and restarting the instance temporarily fixes the issue. The developer suspects a memory leak but cannot add custom instrumentation. Which AWS service can collect memory utilization metrics and help identify the memory leak with minimal configuration?
Question 5
A developer is building a serverless web application using AWS Lambda and Amazon DynamoDB. The application needs to perform complex aggregations on data stored in DynamoDB. Which AWS service should the developer use to perform these aggregations efficiently without reading all the data into Lambda?
Question 6
A developer has an Amazon S3 bucket containing private user documents. The application must generate a time-limited URL for users to download their own documents without requiring the users to have AWS credentials. Which solution should the developer use?
FAQ
Questions learners often ask
What does this DVA-C02 question test?
Static NAT maps one inside address to one outside address.
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. — During a rolling update, ECS deregisters old tasks from the ALB target group after draining existing connections. If the application does not gracefully handle the SIGTERM signal from ECS, it may terminate abruptly while the ALB still routes traffic to it, causing 502 errors. This is a common issue.
What should I do if I get this DVA-C02 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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