DVA-C02 Troubleshooting and Optimization Practice Test 13 — 15 Questions

Question 1

An application uses an Amazon SQS queue to decouple microservices. The producer is sending messages, but the consumer is not processing them. The consumer is an Auto Scaling group of EC2 instances. The SQS queue's ApproximateNumberOfMessagesVisible metric is increasing. What is the MOST likely cause?

Accepted Answer

The consumer instances are not polling the SQS queue.. Option A is correct because if the number of visible messages is increasing, the consumer is not polling or processing fast enough. Option B is wrong because the DLQ would receive messages after max receive count is exceeded, but the visible messages are increasing, indicating messages are not being consumed. Option C is wrong because the visibility timeout being too short would cause messages to reappear after being processed, but the visible count would not increase continuously. Option D is wrong because the queue is receiving messages, so permissions are likely correct.

Answer

The SQS queue policy denies access to the consumer.

Answer

The visibility timeout is set too low.

Answer

The SQS queue has a dead-letter queue configured.

Question 2

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.. Option A is correct because the error indicates that the function code or configuration is being updated while a previous update is still in progress. Option B is wrong because the error is not related to IAM permissions. Option C is wrong because publishing a new version does not conflict with an alias. Option D is wrong because the error is not about exceeding the function code size limit.

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 3

An application running on Amazon ECS with Fargate is unable to connect to the internet. The task definition does not have any network configuration specified. What is the MOST likely cause?

Accepted Answer

The task is not assigned a public IP address and is in a private subnet.. Option C is correct because Fargate tasks running in awsvpc network mode need a route to the internet via a NAT gateway if they are in private subnets. Option A is wrong because tasks can access the internet without an internet gateway if they have a public IP and are in a public subnet. Option B is wrong because security groups control inbound/outbound traffic, but they do not provide internet connectivity. Option D is wrong because ECS service discovery is for service-to-service communication within the VPC.

Answer

The security group associated with the task does not allow outbound traffic.

Answer

The ECS service discovery is not configured.

Answer

The VPC does not have an internet gateway attached.

Question 4

A developer is using Amazon CloudFront to serve static content from an S3 bucket. Users are reporting that they see outdated content. The CloudFront distribution has a default TTL of 24 hours. What is the MOST efficient way to serve updated content immediately?

Accepted Answer

Create a CloudFront invalidation for the updated objects.. Option C is correct because creating an invalidation removes the cached objects from edge locations, forcing CloudFront to fetch the updated content from the origin. Option A is wrong because changing the TTL would affect future cache behavior but not immediately purge existing cached objects. Option B is wrong because updating the object key would require users to use a new URL. Option D is wrong because disabling and re-enabling the distribution would cause downtime.

Answer

Disable and re-enable the CloudFront distribution.

Answer

Update the object key in the S3 bucket.

Answer

Change the default TTL to 0.

Question 5

A developer is troubleshooting an AWS Lambda function that is timing out. The function has a timeout of 5 seconds and is configured with 128 MB of memory. Which TWO of the following are effective ways to resolve the timeout?

Accepted Answer

Increase the memory allocation to 512 MB.. Option A is correct because increasing memory often also increases CPU, which can improve performance. Option C is correct because optimizing the code can reduce execution time. Option B is wrong because increasing timeout alone may not solve the root cause. Option D is wrong because increasing memory is an alternative to increasing timeout. Option E is wrong because deploying in a VPC adds latency due to ENI creation.

Answer

Decrease the memory allocation to 64 MB.

Answer

Deploy the function inside a VPC.

Answer

Increase the function timeout to 10 seconds.

Question 6

A company has a REST API deployed on Amazon API Gateway with a Lambda integration. The API is experiencing high latency. Which TWO actions would help diagnose the issue?

Accepted Answer

Use AWS X-Ray to trace requests.. Option B is correct because enabling detailed CloudWatch logs on API Gateway provides per-request metrics and logs. Option C is correct because AWS X-Ray can trace requests through API Gateway and Lambda to identify bottlenecks. Option A is wrong because increasing Lambda memory might reduce latency but does not help diagnose the cause. Option D is wrong because changing the integration type changes the architecture, not diagnose. Option E is wrong because CloudFront is a CDN and would add complexity.

Answer

Increase the Lambda function memory.

Answer

Change the API integration type from Lambda to HTTP.

Answer

Add Amazon CloudFront in front of API Gateway.

Question 7

A developer is using an Amazon SQS queue with a Lambda function as a consumer. Messages are being sent to the queue but the Lambda function is not processing them. Which THREE of the following are possible causes?

Accepted Answer

The SQS queue policy denies access to the Lambda function.. Option A is correct because the Lambda function may not have permission to poll the queue. Option B is correct because the SQS queue might have a policy that denies access. Option C is correct because the event source mapping might be disabled. Option D is wrong because the DLQ is for failed messages, not for preventing processing. Option E is wrong because SQS has no rate limiting for Lambda polling.

Answer

The SQS queue has a dead-letter queue configured.

Answer

The SQS queue has a rate limit that prevents Lambda from polling.

Question 8

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.. Option C is correct because increasing memory also increases CPU and network throughput, which can reduce execution time. Option A is wrong because Lambda already supports up to 15 minutes. Option B is wrong because increasing memory is a more direct solution than splitting files. Option D is wrong because S3 Event Notifications are configured, not something to add to solve timeout.

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 9

A developer notices that an Amazon RDS for MySQL DB instance's CPU utilization is consistently above 90% during peak hours. Which AWS service can the developer use to analyze the database queries and identify the root cause?

Accepted Answer

Amazon RDS Performance Insights. Option B is correct because Performance Insights provides database performance analysis with query-level metrics. Option A is wrong because CloudWatch Logs is for log data, not query analysis. Option C is wrong because X-Ray traces application requests, not database queries. Option D is wrong because Trusted Advisor provides cost and security checks, not query analysis.

Answer

AWS X-Ray

Answer

Amazon CloudWatch Logs

Answer

AWS Trusted Advisor

Question 10

A company runs a containerized web application on Amazon ECS with Fargate launch type. The application experiences intermittent HTTP 503 errors. The ECS service auto-scales based on CPU, but the errors persist. What is the most likely cause and solution?

Accepted Answer

The ALB health check interval is too short; increase the health check interval.. Option C is correct because 503 errors from ALB suggest targets failing health checks. Increasing health check thresholds gives targets more time to become healthy. Option A is wrong because increasing CPU threshold would reduce scaling, worsening errors. Option B is wrong because Fargate does not use a cluster of EC2 instances. Option D is wrong because errors are 503, not 504 (gateway timeout).

Answer

The CPU threshold is too low; increase the target value to 80%.

Answer

The ALB idle timeout is too low; increase it to 300 seconds.

Answer

The cluster does not have enough EC2 instances; add more instances.

Question 11

A developer is debugging an AWS Lambda function that is invoked by an Amazon S3 bucket notification. The function fails with an 'AccessDenied' error when trying to read an object from the same bucket. What should the developer check first?

Accepted Answer

Review the Lambda function's execution role for s3:GetObject permission.. Option D is correct because the Lambda execution role must have s3:GetObject permission for the bucket. Option A is wrong because S3 Block Public Access does not affect Lambda access. Option B is wrong because encryption settings do not cause AccessDenied if permissions are correct. Option C is wrong because bucket versioning is not related to access.

Answer

Check if S3 bucket versioning is enabled.

Answer

Verify that the S3 bucket uses server-side encryption with AWS KMS.

Answer

Ensure the S3 bucket is not blocked by S3 Block Public Access.

Question 12

An application running on Amazon EC2 instances behind an Application Load Balancer (ALB) is experiencing increased latency. The developer suspects the ALB is the bottleneck. How can the developer confirm this using CloudWatch metrics?

Accepted Answer

Monitor the SurgeQueueLength metric and look for sustained high values.. The SurgeQueueLength metric tracks the number of requests that are queued by the ALB because it cannot route them to a healthy target. A sustained high value indicates that the ALB is overwhelmed and requests are waiting, which directly confirms the ALB as the bottleneck causing increased latency.

Answer

Monitor the HealthyHostCount metric and ensure it is equal to the number of instances.

Answer

Monitor the TargetResponseTime metric and compare it to the client's perspective.

Answer

Monitor the RequestCount metric and check if it exceeds the ALB's limit.

Question 13

A developer is using AWS CodePipeline to deploy a serverless application. The pipeline has a CodeBuild stage that runs unit tests. Recently, the build stage started failing with a 'ResourceNotFoundException: The specified bucket does not exist' error. The buildspec.yml references an artifact bucket. What is the most likely cause?

Accepted Answer

The artifact bucket was deleted or is in a different AWS Region.. Option A is correct because CodePipeline uses a separate artifact bucket owned by the service, which must be in the same region. Option B is wrong because build logs do not affect artifact storage. Option C is wrong because IAM permissions would give AccessDenied, not ResourceNotFound. Option D is wrong because the default artifact bucket is managed by CodePipeline, not CodeBuild.

Answer

The IAM service role for CodeBuild does not have s3:GetObject on the bucket.

Answer

The CodeBuild project does not have permission to write to CloudWatch Logs.

Answer

The buildspec.yml uses an invalid bucket name syntax.

Question 14

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 15

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.. Option C is correct because 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.