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

Question 1

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.

Question 2

A developer runs the AWS CLI command shown in the exhibit. The output includes 'FunctionError': 'Unhandled'. What does this indicate?

Accepted Answer

The function threw an unhandled exception.. 'Unhandled' indicates that the function code threw an exception that was not caught by any try-catch block. Option A is incorrect because a caught error would typically result in a 'Handled' status in the function logs, not 'Unhandled'. Option B is incorrect because a timeout error would produce a different error message, such as 'Task timed out', not 'Unhandled'. Option D is incorrect because an invocation failure (e.g., permissions or configuration issues) would result in an error before the function runs, not an 'Unhandled' function error.

Answer

The function threw an error that was caught by the code.

Answer

The function timed out.

Answer

The function was not invoked successfully.

Question 3

A developer receives an Access Denied error when trying to download an object from an S3 bucket. The developer's IAM policy is shown in the exhibit. The bucket policy also grants access. What is the MOST likely cause?

Accepted Answer

The S3 bucket uses SSE-KMS and the user lacks kms:Decrypt permission.. If the bucket is encrypted with a KMS key, the user must also have kms:Decrypt permission. Option A is wrong because the policy explicitly allows s3:GetObject. Option C is wrong because the bucket policy also grants access, so it's not a bucket policy issue. Option D is wrong because public access is not required if IAM policies allow access.

Answer

The S3 bucket has block public access enabled.

Answer

The IAM policy does not allow s3:GetObject.

Answer

The bucket policy denies access to the user.

Question 4

A developer notices that an Amazon RDS for MySQL DB instance's CPU utilization is consistently above 90% during peak hours. The application uses read-heavy workloads. Which action would MOST effectively reduce CPU load without major architectural changes?

Accepted Answer

Implement an in-memory cache layer with Amazon ElastiCache.. For a read-heavy workload causing sustained high CPU on RDS MySQL, offloading repeated read queries to an in-memory cache like ElastiCache (Redis or Memcached) removes the majority of read traffic from the database engine, directly reducing CPU utilization without re-architecting the application. This is the least invasive and most effective fix for read-dominated load.

Answer

Migrate the database to Amazon Aurora with auto-scaling.

Answer

Increase the DB instance size to a larger instance type.

Answer

Create a Multi-AZ deployment and use the standby for read queries.

Question 5

A developer is troubleshooting an application that uses Amazon SQS. Messages are being sent to a dead-letter queue (DLQ) after the maximum receive count is exceeded. The consumer processes messages but sometimes fails. The developer wants to ensure that messages are retried immediately after a failure, without waiting for the visibility timeout. Which solution should the developer implement?

Accepted Answer

After a failure, call ChangeMessageVisibility with a timeout of 0 to make the message immediately available for reprocessing.. The correct solution is to call ChangeMessageVisibility with a timeout of 0 after a failure. This makes the message immediately available for reprocessing by other consumers, effectively retrying without waiting for the visibility timeout. Option A (delay queue) introduces a delay, which is counterproductive. Option C (delete and re-send) loses original message attributes and is inefficient. Option D (increase visibility timeout) would delay retries, not accelerate them.

Answer

Configure a delay queue so that messages are not immediately visible after failure.

Answer

Delete the message from the queue and re-send it after processing failure.

Answer

Increase the visibility timeout to allow more time for processing.

Question 6

An application running on Amazon ECS Fargate is experiencing intermittent high latency and timeout errors. The application makes API calls to an external third-party service. The ECS service is configured with a target group using HTTP health checks. The ALB health check logs show occasional 503 responses. What is the MOST likely cause?

Accepted Answer

The application is not properly handling timeouts to the third-party service, causing the health check endpoint to hang.. The application's health check endpoint is likely hanging because the application does not handle timeouts when calling the third-party service. This causes the ALB health check to time out and return 503, leading to tasks being marked unhealthy and potentially restarted, which increases latency and timeouts.

Answer

The security group for the ECS tasks is blocking inbound traffic from the ALB.

Answer

The ECS tasks are running out of CPU credits, causing slow response times.

Answer

The ECS service is configured with a task placement strategy that is causing tasks to be stopped and restarted frequently.

Question 7

A developer is troubleshooting a CloudFront distribution that serves static content from an S3 bucket. Users in some geographic locations report slow load times. The developer checks the CloudFront metrics and sees a high number of cache misses. What is the MOST likely cause?

Accepted Answer

The object TTL is set to a very low value (e.g., 0 seconds).. A very low or zero TTL (e.g., 0 seconds) causes CloudFront to treat every request as a cache miss, forcing it to fetch the object from S3 on each request. This increases latency for users, especially in distant geographic locations, because the edge location must repeatedly retrieve the object from the origin. Setting a reasonable TTL allows edge locations to serve cached content and reduces origin fetches.

Answer

The CloudFront distribution is configured with Price Class 100, which uses only the US and Europe edge locations.

Answer

The S3 bucket is configured with signed URLs for access.

Answer

The CloudFront distribution is not configured to compress objects.

Question 8

A developer invokes a Lambda function from the AWS CLI and receives the response shown in the exhibit. The output file contains an error message. What is the MOST likely cause of the FunctionError field being set to 'Unhandled'?

Accepted Answer

The function code threw an uncaught exception.. The FunctionError field set to 'Unhandled' in a Lambda invocation response indicates that the function's code raised an uncaught exception during execution, so option C is correct. AWS Lambda returns this value when the runtime catches an error that the handler did not handle, and the error details appear in the response payload. Option A would typically cause logging failures rather than an 'Unhandled' FunctionError, and could even prevent error details from being logged. Option B is incorrect because the synchronous invocation payload limit is 6 MB, not 6 KB, and exceeding it produces a request validation error, not an 'Unhandled' FunctionError. Option D is incorrect because a timeout produces a different error type (for example, 'Task timed out after X seconds') rather than the generic 'Unhandled' value.

Answer

The function's execution role does not have permission to write to CloudWatch Logs.

Answer

The invocation request payload exceeded the 6 KB limit for synchronous invocation.

Answer

The function timed out before completing execution.

Question 9

A developer uses the CloudFormation template in the exhibit to create an S3 bucket. The stack creation fails with the error 'Bucket already exists'. What is the MOST likely reason?

Accepted Answer

The bucket name is already taken by another AWS account.. S3 bucket names are globally unique across all AWS accounts and regions, so if the name specified in the CloudFormation template is already in use by another account, the stack creation fails with 'Bucket already exists'. This is the most likely cause given the error message. The error is not related to syntax, IAM permissions, or region availability.

Answer

The CloudFormation template has invalid JSON syntax.

Answer

The IAM user does not have permission to create S3 buckets.

Answer

The bucket name is not available in the specified region.

Question 10

A developer is troubleshooting a Lambda function that intermittently times out. The function makes HTTP requests to an external API. The function's CloudWatch logs show 'Task timed out after 3.01 seconds'. What is the MOST likely cause?

Accepted Answer

The Lambda function timeout is set to 3 seconds, but the HTTP request takes longer.. The Lambda function timeout is set to 3 seconds, and the HTTP request to the external API takes longer than that, causing the 'Task timed out after 3.01 seconds' error. Option B is incorrect because throttling due to insufficient reserved concurrency would result in a 'Rate exceeded' error, not a timeout. Option C is incorrect because if the function couldn't reach the external API due to VPC configuration, it would result in a connection error, not a timeout. Option D is incorrect because a missing IAM role would prevent the function from executing at all, and the logs show the function started execution.

Answer

The Lambda function has insufficient reserved concurrency causing throttling.

Answer

The Lambda function is not configured with a VPC and cannot reach the external API.

Answer

The Lambda function is not starting execution due to a missing IAM role.

Question 11

A company runs a production web application on EC2 instances behind an Application Load Balancer. Users report intermittent 502 errors. The developers find that the ALB access logs show 'target_response_code' of 502 for some requests. What is the MOST likely cause?

Accepted Answer

The EC2 instances are closing idle connections prematurely due to a short keep-alive timeout.. The 502 Bad Gateway error from an Application Load Balancer indicates that the target (EC2 instance) closed the connection before the ALB could finish writing the request or reading the response. This commonly occurs when the keep-alive timeout on the EC2 instance is set too low, causing idle connections to be closed prematurely. Option A is incorrect because DNS resolution issues would not cause a 502; they would cause a 503 or connection failure. Option B is incorrect because a security group blocking traffic would result in health check failures and a 503, not a 502. Option D is incorrect because unhealthy instances would cause a 503, not a 502.

Answer

The EC2 instances are unable to resolve DNS for the ALB.

Answer

The security group for the EC2 instances is blocking traffic from the ALB.

Answer

The ALB health checks are failing and the target group has unhealthy instances.

Question 12

A developer is troubleshooting a CloudFormation stack that fails to create. The stack includes an Auto Scaling group with a launch template. The error message says 'Value (null) for parameter groupId is invalid.' What is the MOST likely cause?

Accepted Answer

The launch template references a SecurityGroupId parameter that is not provided or is misspelled.. The error 'Value (null) for parameter groupId is invalid' indicates that a SecurityGroupId parameter referenced in the launch template is either not provided or misspelled. CloudFormation resolves parameters at stack creation; if the parameter is missing or has a typo, it evaluates to null, causing the launch template to fail validation because a security group ID is required for the network interface.

Answer

The Auto Scaling group does not specify a VPC subnet.

Answer

The Auto Scaling group's user data script contains a syntax error.

Answer

The launch template specifies an invalid key pair name.

Question 13

A developer is optimizing an API Gateway REST API that uses Lambda integration. The response times are high, and CloudWatch logs show that the Lambda function has cold starts frequently. The function is written in Java and uses a large library. What is the MOST effective optimization?

Accepted Answer

Enable provisioned concurrency on the Lambda function.. The most effective optimization is C: enabling provisioned concurrency on the Lambda function, because it pre-initializes execution environments so that invocations are served by already-warm instances, eliminating the cold starts that CloudWatch logs show are frequent. This directly addresses the Java runtime's heavy initialization cost caused by the large library, without changing application code. Option A is a major rewrite that may reduce cold start duration but does not guarantee elimination and changes the technology stack. Option B increases memory and can proportionally speed initialization, but cold starts would still occur. Option D may modestly improve Java initialization, but it does not prevent cold starts the way provisioned concurrency does.

Answer

Rewrite the function in Node.js to reduce cold start time.

Answer

Increase the Lambda function's memory allocation to 3008 MB.

Answer

Use the AWS SDK for Java 2.x to reduce initialization time.

Question 14

A developer is troubleshooting an Amazon RDS for MySQL instance that is experiencing high CPU utilization. The application performs many read operations. The developer wants to reduce the load on the database. What is the MOST effective solution?

Accepted Answer

Create a read replica and direct read queries to it.. Creating a read replica allows read queries to be directed to the replica, offloading the read workload from the primary instance and reducing its CPU utilization. Option A is incorrect because upgrading to a larger instance class increases capacity but does not specifically address read-heavy workloads efficiently and is less cost-effective than scaling reads with replicas. Option C is incorrect because Multi-AZ provides high availability and automatic failover, not performance improvement or load reduction. Option D is incorrect because purchasing reserved instances reduces costs but does not affect CPU utilization.

Answer

Upgrade the DB instance to a larger instance class.

Answer

Enable Multi-AZ for automatic failover.

Answer

Purchase reserved instances to reduce costs.

Question 15

A company is using AWS CodePipeline for CI/CD. The pipeline has a build stage using AWS CodeBuild, and a deploy stage using AWS CodeDeploy. The deployment is failing with 'Error: Health checks failed'. Which TWO steps should the developer take to troubleshoot this issue? (Select TWO.)

Accepted Answer

Verify that the target group's health check path and port are correctly configured.. Options A and C are correct. Verifying the target group's health check path and port (A) ensures that the load balancer's health check matches the application's actual endpoint, which is a common cause of health check failures. Checking the CodeDeploy deployment logs (C) provides detailed error messages from the deployment process, which can pinpoint why the health checks are failing. Option B (checking S3 bucket) is not directly related to health check failures, as artifacts are typically stored correctly if the build succeeded. Option D (checking CodeBuild logs) is irrelevant because the build stage succeeded. Option E (increasing instances) does not address the root cause of health check failures.

Answer

Check the S3 bucket where the build artifacts are stored.

Answer

Check the CodeBuild build logs for errors.

Answer

Increase the number of EC2 instances in the Auto Scaling group.