DVA-C02 Troubleshooting and Optimization Practice Test 18 — 15 Questions

Question 1

An application running on EC2 instances behind an Application Load Balancer (ALB) occasionally returns HTTP 503 errors. The instances are in an Auto Scaling group. Which action should be taken to resolve this issue?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

Review the ALB access logs to identify the target response codes.. HTTP 503 errors from an ALB indicate that the targets (EC2 instances) are not responding successfully. Reviewing ALB access logs reveals the specific target response codes (e.g., 503 from the target itself or connection timeouts), which helps pinpoint whether the issue is due to overloaded instances, application errors, or health check failures. This diagnostic step is essential before making any configuration changes.

Answer

Enable cross-zone load balancing on the ALB.

Answer

Increase the ALB idle timeout setting.

Answer

Increase the size of the EC2 instances.

Question 2

A developer is deploying a new version of a Lambda function using an alias for blue/green deployment. Traffic is gradually shifted to the new version. During the shift, a high error rate is observed. What should the developer do to minimize impact?

Accepted Answer

Configure the alias with a canary deployment and an error rate alarm for automatic rollback.. It automates the rollback process using AWS CodeDeploy's canary deployment with an Amazon CloudWatch alarm on the error rate. When the alarm triggers, CodeDeploy automatically shifts traffic back to the previous version, minimizing impact without manual intervention. This is the recommended approach for safe blue/green deployments with Lambda aliases.

Answer

Use the Lambda function's provisioned concurrency to pre-warm the new version.

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Manually revert the alias to point back to the old version.

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Delete the new version and redeploy after fixing the issue.

Question 3

A company uses AWS CodePipeline with CodeBuild to test and deploy a web application. The pipeline has been failing at the deploy stage with an error: 'Access Denied'. CloudTrail shows the CodePipeline service role is making the call. What is the MOST likely cause?

Accepted Answer

The CodePipeline service role lacks permissions for the deploy action.. The error 'Access Denied' in the deploy stage, with CloudTrail showing the CodePipeline service role making the call, indicates that the IAM role assumed by CodePipeline does not have the necessary permissions to perform the deploy action against the target provider (e.g., ECS, S3, Elastic Beanstalk). CodePipeline uses its service role to invoke the deploy action, and if that role lacks the required `codedeploy:*`, `s3:PutObject`, or `ecs:UpdateService` permissions, the API call will be denied.

Answer

The CodeBuild project does not have internet access.

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The deploy provider (e.g., ECS, S3) is not in the same AWS region.

Answer

The source code repository does not have the correct branch.

Question 4

A developer is troubleshooting a slow-running query in Amazon RDS for MySQL. The query is used by a reporting dashboard. Which AWS service should the developer use to identify the bottleneck?

Accepted Answer

Amazon RDS Performance Insights. Amazon RDS Performance Insights provides a detailed analysis of database performance, including wait events and SQL query performance, helping identify bottlenecks.

Answer

AWS X-Ray

Answer

AWS CloudTrail

Answer

Amazon CloudWatch Logs

Question 5

A developer has deployed a serverless application using AWS SAM. After a recent update, the API Gateway endpoints return 500 errors. The Lambda function logs show no errors. What should the developer investigate first?

Accepted Answer

Verify the API Gateway integration response and mapping templates.. When API Gateway returns 500 errors but Lambda logs show no errors, the issue is typically in the API Gateway integration response or mapping templates. API Gateway may fail to transform the Lambda response into the expected format, causing an internal server error without the Lambda function ever throwing an exception.

Answer

Increase the Lambda function timeout.

Answer

Check the Lambda function's reserved concurrency.

Answer

Review the CloudFormation stack events for any failures.

Question 6

A developer is using AWS X-Ray to trace requests through a microservices application. One of the services, Service B, is not appearing in the trace map. What is the MOST likely reason?

Accepted Answer

Service B is not instrumented with the X-Ray SDK.. For X-Ray to trace requests across services, each service must be instrumented with the X-Ray SDK. If Service B is not instrumented, it won't send trace data, and it won't appear in the trace map.

Answer

Service B is using HTTP/2, which is not supported by X-Ray.

Answer

Service B is running in a different AWS region.

Answer

The X-Ray sampling rate is set too low.

Question 7

A developer is troubleshooting an EC2 instance that is unreachable via SSH. The instance is in a public subnet with a security group that allows inbound SSH from 0.0.0.0/0. Which THREE are possible causes? (Choose 3.)

Accepted Answer

The network ACL associated with the subnet is blocking inbound SSH.. Option A is correct because a network ACL is a stateless subnet-level firewall, so even if the security group allows inbound TCP port 22 from 0.0.0.0/0, an NACL rule denying inbound SSH (and the corresponding outbound ephemeral ports) will block the connection. Option C is correct because an EC2 instance in the 'stopped' state has no running OS or network stack, so SSH cannot be served regardless of subnet, security group, or IP configuration. Option E is correct because an instance in a public subnet is only reachable from the internet if it has a public IPv4 address (or an Elastic IP); without one, external SSH clients have no routable destination. Option B is not a valid cause here because an incorrect SSH key pair would cause authentication failure after the TCP connection is established, not make the instance unreachable. Option D is not a valid cause because IAM roles govern AWS API permissions, not inbound SSH access to the instance's operating system.

Answer

The SSH key pair used to launch the instance is incorrect.

Answer

The instance does not have an IAM role with the necessary permissions.

Question 8

A developer notices that the Lambda function 'my-function' is not generating any logs in CloudWatch, although the function is invoked successfully. The developer runs the command above. What is the MOST likely cause?

Accepted Answer

The Lambda function's execution role is missing the 'logs:CreateLogStream' and 'logs:PutLogEvents' permissions.. The log group exists but has 0 stored bytes, meaning no log streams have been created. This typically indicates that the Lambda function's execution role does not have permissions to create log streams and put log events. The function runs but fails silently to write logs.

Answer

The log group retention policy is set to 0 days.

Answer

The Lambda function is configured to log to a custom log group.

Answer

The Lambda function has reserved concurrency set to 0.

Question 9

A developer is troubleshooting a slow Amazon RDS MySQL database query. The query is frequently executed and takes 5 seconds to complete. Which AWS service should the developer use to analyze the query performance?

Accepted Answer

Amazon RDS Performance Insights. Amazon RDS Performance Insights is the correct service to analyze query performance on an RDS MySQL database. It provides a dashboard that visualizes database load and helps identify the top SQL statements, wait events, and users consuming the most resources. This allows the developer to pinpoint the slow query and understand its impact.

Answer

AWS CloudTrail

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Amazon CloudWatch Logs

Answer

AWS X-Ray

Question 10

A developer is deploying a new version of an application to Amazon ECS using the Fargate launch type. The task fails to start and the error message indicates that the task cannot pull the container image from Amazon ECR. What is the MOST likely cause?

Accepted Answer

The task execution role lacks permissions to pull from ECR.. The error message indicates a failure to pull the container image from Amazon ECR. The task execution role must have permissions such as ecr:GetDownloadUrlForLayer and ecr:BatchGetImage to pull images. Option A is wrong because the task definition family name does not affect image pulling. Option C is wrong because Fargate does not use host port mapping; container port mapping is handled automatically. Option D is wrong because insufficient CPU or memory typically results in a different error (e.g., task stuck in provisioning), not an image pull failure.

Answer

The task definition family name is incorrect.

Answer

The container port is not mapped to a host port.

Answer

The CPU or memory limits are too low for the container.

Question 11

A developer configured an S3 bucket to trigger a Lambda function on object creation. The Lambda function processes the object and then deletes it. Some objects are not being processed. What should the developer do to ensure all objects are processed?

Accepted Answer

Send S3 events to an SQS queue and configure the Lambda function to poll the queue.. Sending S3 events to an SQS queue decouples event delivery from Lambda invocation. If the Lambda function fails or throttles, the event remains in the queue and can be retried, ensuring no objects are missed. Without a queue, S3 events that fail to invoke Lambda (e.g., due to concurrency limits) are lost, leading to unprocessed objects.

Answer

Assign a new IAM role to the Lambda function with S3 permissions.

Answer

Enable S3 versioning on the bucket.

Answer

Increase the Lambda function timeout.

Question 12

A company is using Amazon DynamoDB with on-demand capacity. A developer notices that write requests are being throttled during peak hours. What is the MOST effective way to resolve this issue?

Accepted Answer

Review the partition key design and consider adding a suffix to distribute writes.. DynamoDB on-demand mode automatically scales to accommodate traffic, so throttling during peak hours usually indicates a hot partition caused by an unevenly distributed partition key. Adding a suffix (write sharding) distributes writes across more partitions, eliminating the hot partition and resolving throttling without changing capacity mode.

Answer

Switch to provisioned capacity mode with auto-scaling.

Answer

Increase the write capacity units.

Answer

Increase the read capacity units.

Question 13

A developer is troubleshooting an AWS CloudFormation stack creation failure. The stack creation failed with the error: 'Resource creation cancelled'. What does this error typically indicate?

Accepted Answer

Another resource in the stack failed, causing a rollback.. 'Resource creation cancelled' is CloudFormation's generic message when a resource's creation is aborted because another resource in the same stack failed and CloudFormation initiated a rollback. By default, stack creation uses rollback-on-failure, so once any resource fails, all in-progress creations are cancelled and successfully created resources are deleted. The error is a symptom of a sibling resource failure, not a problem with the cancelled resource itself.

Answer

The IAM user does not have permission to create the resource.

Answer

The template has a syntax error.

Answer

The resource type is not supported by CloudFormation.

Question 14

A developer is using AWS Elastic Beanstalk to deploy a web application. The application is experiencing high latency. Which TWO steps should the developer take to troubleshoot and optimize the application?

Accepted Answer

Enable AWS X-Ray integration and analyze service maps.. AWS X-Ray integration provides tracing to identify bottlenecks in the application. Option C is correct because enhanced health reporting gives detailed environment health metrics for troubleshooting. Option A is wrong because an RDS read replica is for database read scaling, not directly for latency troubleshooting. Option D is wrong because increasing the instance type is a scaling solution, not a troubleshooting step. Option E is wrong because deploying to a different region does not address latency for existing users.

Answer

Configure an Amazon RDS read replica.

Answer

Increase the instance type to a larger size.

Answer

Deploy the application to a different AWS region.

Question 15

A developer is optimizing an AWS Lambda function that processes streaming data from Amazon Kinesis. The function is CPU-bound. Which TWO actions should the developer take to improve performance?

Accepted Answer

Rewrite the function in a compiled language like Go.. Option A is correct because rewriting a CPU-bound Lambda function in a compiled language such as Go reduces execution time: Go compiles to native machine code, avoids the JIT warm-up and higher memory overhead of interpreted runtimes like Python or Node.js, and typically delivers significantly faster CPU throughput for the same work. Option C is correct because in AWS Lambda, CPU power scales proportionally with the configured memory allocation; increasing memory from, say, 512 MB to 1769 MB grants roughly one full vCPU, which directly speeds up CPU-bound processing. Option B is wrong because reserved concurrency only caps or guarantees the number of simultaneous invocations; it does not make any single invocation faster and can even throttle throughput if set too low. Option D is wrong because increasing Kinesis shard count raises stream throughput and parallelism across records, but it does not accelerate the CPU-bound work inside one function invocation. Option E is wrong because AWS Lambda does not support GPU acceleration; GPU-backed compute requires services like Amazon EC2, ECS, or SageMaker.

Answer

Increase the function's reserved concurrency.

Answer

Increase the Kinesis stream's shard count.

Answer

Enable GPU acceleration for the function.