DVA-C02 Troubleshooting and Optimization Practice Test 19 — 15 Questions

Question 1

A company is using Amazon API Gateway to expose a REST API. The API is integrated with an AWS Lambda function. Lately, the API is returning 502 Bad Gateway errors. What is the MOST likely cause?

Accepted Answer

The Lambda function is returning an unhandled exception.. A 502 Bad Gateway error from API Gateway typically indicates that the backend integration (in this case, the Lambda function) returned an error response. When a Lambda function throws an unhandled exception, API Gateway receives a 200 OK with a function error payload, but it cannot parse the response into a valid HTTP response, resulting in a 502. This is distinct from throttling or permission issues, which produce different HTTP status codes.

Answer

The API Gateway request throttling limit has been exceeded.

Answer

The API Gateway API key is invalid.

Answer

The Lambda function's execution role does not allow API Gateway to invoke it.

Question 2

A developer is using Amazon DynamoDB with provisioned throughput. The application is receiving ProvisionedThroughputExceededException errors. What is the BEST way to handle this error?

Accepted Answer

Implement exponential backoff and retry in the application code.. The ProvisionedThroughputExceededException indicates that the application has exceeded the provisioned read/write capacity units for the DynamoDB table. The best practice to handle this error is to implement exponential backoff and retry logic in the application code, which progressively increases the wait time between retries to reduce request volume and allow the throttling to subside. This approach is recommended by AWS for handling throttling errors gracefully without manual intervention.

Answer

Contact AWS Support to increase the DynamoDB service limits.

Answer

Reduce the read and write capacity units.

Answer

Switch the table to on-demand capacity mode.

Question 3

A developer is deploying a new version of an AWS Lambda function using the AWS CLI. The deployment fails with a 'ResourceConflictException' error. What is the MOST likely cause?

Accepted Answer

Another deployment is currently in progress for the same Lambda function.. The 'ResourceConflictException' error in AWS Lambda occurs when you attempt to update a Lambda function while another update operation is already in progress. Lambda enforces a single in-flight update per function to prevent race conditions and ensure state consistency. The AWS CLI command (e.g., update-function-code) will fail immediately if a previous deployment has not completed, even if the previous deployment was triggered by the same or a different client.

Answer

The Lambda function code exceeds the maximum allowed size.

Answer

The Lambda function has an alias that conflicts with the version number.

Answer

The IAM role associated with the Lambda function does not have sufficient permissions.

Question 4

A developer is troubleshooting an AWS Lambda function that times out when processing large files from Amazon S3. The function has a 15-minute timeout and 512 MB memory. What should the developer do to resolve this issue?

Accepted Answer

Increase the Lambda function memory to 3008 MB.. Increasing the Lambda function memory to 3008 MB is correct because Lambda allocates CPU proportionally to memory, and more CPU reduces processing time for CPU-bound tasks like file parsing. The 15-minute timeout is already the maximum, so the issue is insufficient compute resources, not timeout duration. With 512 MB, the function lacks the CPU throughput to process large files within the timeout, so boosting memory (and thus CPU) directly addresses the root cause.

Answer

Use Amazon S3 batch operations to split the files before processing.

Answer

Add an S3 Event Notification to trigger the function asynchronously.

Answer

Reduce the Lambda timeout to 5 minutes to force faster processing.

Question 5

A developer deploys a new version of an AWS Lambda function using the AWS CLI. After deployment, the function returns stale results. What is the most likely cause?

Accepted Answer

The Lambda function alias is still pointing to the previous version.. When a developer deploys a new version of a Lambda function using the AWS CLI without updating the function alias, the alias continues to point to the previous version. Invoking the function via the alias (e.g., via an API Gateway endpoint or a CloudFront origin) will execute the old code, returning stale results. The `$LATEST` version is updated, but unless the alias is repointed, it does not automatically use the new code.

Answer

The function's environment variables are cached and not updated.

Answer

The Amazon CloudFront distribution is caching the old response.

Answer

The Lambda function's code is cached by the Lambda service.

Question 6

A company's application uses Amazon DynamoDB as its database. The application reads the same item multiple times per second and occasionally sees stale data. The DynamoDB table uses the default eventually consistent reads. What should the developer change to ensure strongly consistent reads?

Accepted Answer

Set the ConsistentRead parameter to true in the GetItem call.. DynamoDB's default read consistency model is eventually consistent, which can return stale data if an item is updated shortly before the read. By setting the `ConsistentRead` parameter to `true` in the `GetItem` call, the developer forces a strongly consistent read, ensuring the response reflects the most recent write. This directly addresses the stale data issue without changing throughput or adding caching.

Answer

Increase the read capacity units of the table.

Answer

Use DynamoDB Accelerator (DAX) to cache the item.

Answer

Use DynamoDB transactions for all read operations.

Question 7

A company's application runs on Amazon EC2 instances in an Auto Scaling group. The application experiences intermittent failures, and the developer suspects the application is not properly handling termination notifications. Which TWO steps should the developer take to diagnose the issue?

Accepted Answer

Configure a CloudWatch Events rule to capture Auto Scaling termination events.. Options B and D are correct. B: CloudWatch Events can capture termination events, which can be used to trigger notifications. D: Lifecycle hooks allow the instance to perform actions before termination. Option A is wrong because detailed monitoring does not capture termination signals. Option C is wrong because CloudWatch Logs agent is for logs, not for termination notifications. Option E is wrong because replacing instances does not diagnose the issue.

Answer

Enable detailed monitoring on the Auto Scaling group.

Answer

Install the CloudWatch Logs agent on the instances to capture application logs.

Answer

Use an Elastic Load Balancer to replace instances automatically.

Question 8

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?

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 9

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.

Answer

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

Answer

Delete the new version and redeploy after fixing the issue.

Question 10

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.

Answer

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 11

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 12

A developer notices that an AWS Lambda function is timing out after 3 seconds. The function processes messages from an SQS queue. What is the MOST likely cause of the timeout?

Accepted Answer

The Lambda function timeout is set too low.. The Lambda function is timing out after 3 seconds, which matches the default Lambda timeout. The most likely cause is that the function timeout is set too low (3 seconds) and needs to be increased to accommodate processing time. Option B (SQS visibility timeout) affects message redelivery but not the Lambda execution timeout. Option D (reserved concurrency set to zero) would prevent any invocations, not cause a timeout after 3 seconds. Option A (dead-letter queue not configured) does not cause timeouts; it only affects where failed messages go.

Answer

The SQS dead-letter queue is not configured.

Answer

The SQS queue visibility timeout is too short.

Answer

The Lambda function's reserved concurrency is set to zero.

Question 13

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 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 company is using Amazon S3 to store large objects. Users report that uploads are slow. Which THREE actions should the developer take to optimize upload performance?

Accepted Answer

Use multipart upload for objects over 100 MB.. Multipart upload improves throughput for large objects over 100 MB by uploading parts in parallel. Option C is correct because S3 Transfer Acceleration uses CloudFront edge locations to reduce latency for uploads over long distances. Option E is correct because using multiple S3 prefixes (i.e., parallelizing requests across different key prefixes) can increase the request rate and overall throughput. Option B is incorrect because S3 Select is used to retrieve subsets of data from an object, not to upload. Option D is incorrect because transitioning to S3 Glacier is for data lifecycle management, not for improving upload performance.

Answer

Use S3 Select to upload only specific parts of the object.

Answer

Transition objects to S3 Glacier after upload.