DVA-C02 Troubleshooting and Optimization Practice Test 11 — 15 Questions

Question 1

A developer runs a script that uses the AWS CLI to copy a large number of files from an on-premises server to an S3 bucket. The copy operation fails partway through with a 'RequestTimeout' error. What is the MOST efficient way to resume the copy and ensure all files are transferred?

Accepted Answer

Use the aws s3 sync command to synchronize the source directory with the S3 bucket.. The `aws s3 sync` command is the most efficient way to resume the copy because it automatically compares the source directory with the destination S3 bucket and transfers only the files that are missing or have been modified. This avoids re-uploading already transferred files, directly addressing the partial failure without manual intervention or unnecessary overhead.

Answer

Delete the S3 bucket and restart the copy operation.

Answer

Use the cp command with the --recursive flag to copy the remaining files.

Answer

Increase the --cli-read-timeout value in the AWS CLI configuration and retry the original command.

Question 2

A developer deploys an application on EC2 instances behind an Application Load Balancer (ALB). The application uses sticky sessions (session affinity) based on a cookie. Users report that they are intermittently logged out during their session. What is the MOST likely cause?

Accepted Answer

The stickiness cookie expiration duration is set too low, causing the cookie to expire before the user's session ends.. Option C is correct because if the stickiness cookie duration is shorter than the user's session, the load balancer may route the user to a different instance, losing session state. Option A is wrong because cross-zone load balancing distributes traffic but does not affect stickiness. Option B is wrong because deregistration delay affects instance draining, not stickiness. Option D is wrong because health checks do not remove cookies.

Answer

The deregistration delay value is too low, causing connections to be dropped during scaling events.

Answer

The ALB health check interval is too short, causing healthy instances to be marked unhealthy frequently.

Answer

Cross-zone load balancing is disabled, causing uneven traffic distribution.

Question 3

A company runs a microservices application on Amazon ECS with Fargate. The application includes a service that processes messages from an SQS queue. The service's CPU utilization is consistently above 80%, and messages are accumulating in the queue. The service is configured with a desired count of 2 tasks and auto scaling based on CPU utilization. What should a developer do to improve message processing throughput?

Accepted Answer

Change the auto scaling metric to use the SQS queue's ApproximateNumberOfMessagesVisible.. Option A is correct because using SQS-based metrics (e.g., ApproximateNumberOfMessagesVisible) for auto scaling is more responsive to queue depth than CPU utilization. Option B is wrong because increasing task size may help but does not address the scaling trigger. Option C is wrong because increasing desired count without scaling policy will not adapt. Option D is wrong because reducing batch size reduces throughput.

Answer

Increase the desired count of tasks to 5.

Answer

Increase the task size to use more CPU and memory.

Answer

Decrease the batch size of messages polled from SQS.

Question 4

A developer is troubleshooting an AWS Lambda function that writes to an S3 bucket. The function is configured with a resource-based policy that allows the S3 service to invoke the function. However, the function fails with an access denied error when trying to write to S3. What is the MOST likely cause?

Accepted Answer

The Lambda function's execution role does not have an IAM policy that allows s3:PutObject.. Option D is correct because the Lambda function needs an execution role with permissions to write to S3. The resource-based policy only allows S3 to invoke the function, not the function to write. Option A is wrong because bucket policy is not needed if the execution role has permissions. Option B is wrong because the function can be triggered correctly. Option C is wrong because VPC does not cause access denied.

Answer

The Lambda function is configured in a VPC without an S3 VPC endpoint.

Answer

The Lambda function's trigger (S3 event notification) is misconfigured.

Answer

The S3 bucket policy does not grant the Lambda function write access.

Question 5

A developer is using Amazon DynamoDB as the database for a web application. The application experiences occasional spikes in traffic, and some write requests fail with a ProvisionedThroughputExceededException. What is the MOST cost-effective way to handle these spikes without manual intervention?

Accepted Answer

Enable DynamoDB auto scaling for the table.. Option A is correct because DynamoDB auto scaling automatically adjusts capacity based on traffic, handling spikes without manual intervention. Option B is wrong because it increases cost continuously. Option C is wrong because it requires manual changes. Option D is wrong because it does not help with write throughput.

Answer

Switch to on-demand mode for the table.

Answer

Increase the provisioned write capacity to the peak expected value.

Answer

Use DynamoDB Accelerator (DAX) to cache writes.

Question 6

A developer is troubleshooting a slow-running query on an Amazon RDS for MySQL database. The query is used by a reporting application and takes over 30 seconds to complete. The database is a db.r5.large instance with 200 GB of gp2 storage. Which TWO actions should the developer take to improve query performance?

Accepted Answer

Review the slow query log to identify the query and its execution plan.. Option A and D are correct: reviewing the slow query log helps identify the query, and adding appropriate indexes can speed up execution. Option B is wrong because increasing storage does not directly improve query speed. Option C is wrong because terminating idle connections has no impact. Option E is wrong because Multi-AZ is for high availability, not performance.

Answer

Terminate idle connections to free up resources.

Answer

Increase the allocated storage to 500 GB to improve I/O performance.

Answer

Enable Multi-AZ deployment for better read performance.

Question 7

A company is running a serverless application using AWS Lambda and Amazon API Gateway. The application experiences increased latency during peak hours. CloudWatch metrics show that Lambda function duration remains stable, but API Gateway latency spikes. Which THREE actions should the developer take to reduce API Gateway latency?

Accepted Answer

Enable compression for API responses.. Options A, B, and D are correct. Enabling caching reduces backend calls, using Regional endpoint reduces network latency, and enabling compression reduces payload size. Option C is wrong because throttling limits do not reduce latency. Option E is wrong because increasing Lambda timeout does not affect API Gateway latency.

Answer

Increase the Lambda function timeout.

Answer

Increase the API Gateway throttling limits.

Question 8

A developer is deploying a new microservice on AWS Elastic Beanstalk. The service uses an RDS database. The developer wants to ensure that database credentials are not stored in the application's source code. Which TWO methods should the developer use to securely provide credentials to the application?

Accepted Answer

Use AWS Secrets Manager to store and retrieve the credentials at runtime.. Options B and D are correct. Elastic Beanstalk can set environment variables from a source, and AWS Secrets Manager is a secure service for managing secrets. Option A is wrong because the source code is not secure. Option C is wrong because an S3 bucket with a public policy is insecure. Option E is wrong because EC2 Parameter Store is a better name for Systems Manager Parameter Store, but the concept is correct; however, Secrets Manager is more appropriate for credentials.

Answer

Store the credentials in a configuration file within the application source code.

Answer

Store the credentials in an encrypted file on an EC2 instance.

Answer

Store the credentials in an S3 bucket with a public read policy.

Question 9

The exhibit shows the output of invoking a Lambda function from the AWS CLI. The function returned a status code of 200 but included a FunctionError field set to 'Unhandled'. What does this indicate?

Accepted Answer

The function executed but threw an unhandled exception.. Option C is correct because FunctionError: 'Unhandled' means the function threw an exception that was not caught by the code. Option A is wrong because status code 200 indicates invocation succeeded. Option B is wrong because LogResult is base64-encoded logs, not error. Option D is wrong because the function ran but threw an error.

Answer

The function returned an error in the LogResult field.

Answer

The function timed out during execution.

Answer

The function was invoked but there was a network error.

Question 10

The exhibit shows an IAM policy attached to a Lambda function's execution role. The function writes objects to an S3 bucket that is encrypted with a KMS key (the key specified in the policy). When the function tries to write an object, it receives an access denied error. What is the MOST likely missing permission?

Accepted Answer

kms:GenerateDataKey is missing.. Option B is correct because to write an encrypted object, the function needs kms:GenerateDataKey or kms:Encrypt permission. Option A is wrong because s3:PutObject is allowed. Option C is wrong because KMS key policy might be restrictive, but the most direct missing permission is kms:GenerateDataKey. Option D is wrong because kms:ReEncrypt is not needed.

Answer

The KMS key policy does not allow the Lambda function role.

Answer

s3:GetObject is missing for the bucket.

Answer

kms:ReEncrypt is missing.

Question 11

The exhibit shows a CloudFormation template that creates an S3 bucket with versioning enabled. After deploying the stack, a developer uploads an object to the bucket. Later, the developer updates the object by uploading a new version. The developer wants to retrieve the original object. What is the correct way to do this?

Accepted Answer

Use the S3 console or CLI to list object versions and retrieve the version ID of the original object.. Option A is correct because versioning allows preserving and retrieving previous versions. Option B is wrong because there is no undo in S3. Option C is wrong because the original is still present as a previous version. Option D is wrong because only the latest version is returned by default.

Answer

Restore the original object using the S3 Object Lambda.

Answer

Use the S3 Batch Operations to revert to the original version.

Answer

The original object is overwritten and cannot be retrieved.

Question 12

A company has a production application running on Amazon ECS with Fargate. The application consists of a front-end service and a backend service that processes orders. The backend service consumes messages from an Amazon SQS queue and writes order records to an Amazon DynamoDB table. Recently, during a marketing campaign, traffic increased significantly, causing the backend service to fall behind processing messages. The SQS queue depth grew to over 100,000 messages, and some orders were not processed in time, leading to customer complaints. The operations team noticed that the ECS service's CPU utilization never exceeded 60%, and memory utilization was around 50%. The service is configured with a desired count of 2 tasks and a target tracking scaling policy based on average CPU utilization. The DynamoDB table has on-demand capacity mode. After analyzing the logs, the development team found that each message processing takes about 2 seconds, but the backend service has a bottleneck: it makes an HTTP call to a third-party API that sometimes takes up to 10 seconds to respond. The team wants to optimize the architecture to handle traffic spikes better without over-provisioning resources.

Which solution is MOST effective?

Accepted Answer

Refactor the backend service to send the order processing request to a separate SQS queue and have a dedicated set of tasks poll that queue to make the HTTP call. This decouples the main processing from the slow API call.. Option A is correct because the bottleneck is the third-party API call. Moving the call to a separate step function or SQS queue allows the ECS service to offload that work and process more messages concurrently. Option B is wrong because increasing tasks may not help if the bottleneck is the API latency. Option C is wrong because changing scaling metric to memory is not addressing the root cause. Option D is wrong because increasing batch size may increase per-invocation time and exacerbate the bottleneck.

Answer

Increase the batch size of messages polled from SQS to 20 to process more messages per task.

Answer

Increase the desired count of the ECS service to 10 tasks and set a target tracking scaling policy based on SQS queue depth.

Answer

Change the scaling policy to use memory utilization instead of CPU, since CPU is underutilized.

Question 13

A developer is working on a serverless application that uses AWS Lambda functions to process user uploads. The uploads are stored in an S3 bucket, and each upload triggers a Lambda function that resizes images and stores metadata in DynamoDB. Recently, users have reported that some images are not being resized. The developer checks the CloudWatch logs and sees that the Lambda function is invoked, but it fails with a timeout error after 15 seconds for a few large images. The function has a timeout of 15 seconds and a memory of 512 MB. The image sizes vary from 1 MB to 50 MB. The developer wants to handle large images without increasing the timeout significantly, as that would increase costs. The function is CPU-bound during image processing. Which solution should the developer implement?

Accepted Answer

Increase the memory allocated to the Lambda function to 3008 MB, which also increases CPU power, allowing faster processing within the same timeout.. Option B is correct because increasing memory also increases CPU allocation in Lambda, which speeds up processing. Option A is wrong because splitting the image is complex and may not help. Option C is wrong because moving to Step Functions adds complexity and still needs processing time. Option D is wrong because increasing timeout alone may not help if CPU is the bottleneck.

Answer

Split the large images into smaller chunks before uploading to S3, then reassemble them after processing.

Answer

Increase the Lambda function timeout to 5 minutes to accommodate large images.

Answer

Use AWS Step Functions to orchestrate the image processing workflow, allowing longer timeouts for individual steps.

Question 14

A company runs a critical application on Amazon EC2 instances behind an Application Load Balancer (ALB). The application experiences intermittent errors where some requests return HTTP 503 (Service Unavailable) errors. The developers have verified that the application code is healthy and the EC2 instances pass health checks. The ALB health check is configured to hit a specific endpoint (/health) with a healthy threshold of 2 and an unhealthy threshold of 2. The health check interval is 30 seconds, and the timeout is 5 seconds. The application's /health endpoint sometimes takes up to 6 seconds to respond due to a dependency on a third-party service. The developers want to minimize the 503 errors without changing the application code. Which action should the developer take?

Accepted Answer

Increase the health check timeout to 10 seconds to accommodate the slow /health endpoint.. Option C is correct because increasing the health check timeout to 10 seconds ensures that the ALB does not mark instances as unhealthy prematurely. Option A is wrong because decreasing the interval may cause more frequent health checks, increasing load. Option B is wrong because decreasing the unhealthy threshold may make instances appear unhealthy more quickly. Option D is wrong because deregistration delay does not affect health checks.

Answer

Decrease the unhealthy threshold to 1 so that instances are marked unhealthy after one failed health check.

Answer

Increase the deregistration delay to 300 seconds to allow connections to drain.

Answer

Decrease the health check interval to 10 seconds to detect health changes faster.

Question 15

A developer deployed a new Lambda function that processes messages from an SQS queue. The function runs correctly for small workloads but starts timing out after 15 seconds when traffic increases. The function has a reserved concurrency of 10 and a timeout of 30 seconds. CloudWatch logs show occasional throttling errors (429). What is the MOST likely cause?

Accepted Answer

The reserved concurrency is too low.. Option D is correct because the function is experiencing throttling due to insufficient reserved concurrency, causing requests to be delayed and eventually time out. Option A is wrong because the timeout is set to 30 seconds, but the issue is throttling, not timeout. Option B is wrong because SQS batch size does not cause throttling. Option C is wrong because Lambda scales horizontally, not vertically.

Answer

The function memory is too low.

Answer

The SQS batch size is too large.

Answer

The function timeout is too low.