Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
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?
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
Best answer
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
Distractor review
The ALB's idle timeout is set too low, causing dropped connections
Idle timeout affects persistent connections but does not cause 503 errors due to insufficient healthy hosts.
C
Distractor review
The Auto Scaling group's maximum capacity of 10 is insufficient
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
Distractor review
The health check grace period is preventing instances from being marked healthy
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 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 Auto Scaling group's cooldown period prevents new instances from being added quickly enough during rapid traffic spikes — A simple scaling policy has a cooldown period (default 300 seconds) after a scaling activity. If traffic spikes rapidly and the CPU exceeds 70% for 5 minutes, a scaling activity adds 2 instances, but then cooldown prevents further scaling. If the spike continues and the new instances are quickly overwhelmed, the ALB may mark instances as unhealthy if they fail health checks, leading to zero healthy hosts. The issue is that the scaling policy is too slow and the cooldown prevents rapid scaling to meet demand. Target tracking scaling policies could react faster and are recommended. Insufficient max instances (10) is less likely because the max is high. Stickiness or health check settings could contribute but are not the root cause given the intermittent nature tied to scaling cooldown.
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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