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

Question 1

A developer is deploying a serverless application using AWS CloudFormation. The stack creation fails with the error 'The following resource(s) failed to create: [MyLambdaFunction]'. The developer checks the CloudWatch logs but finds no logs for the Lambda function. What is the most likely reason?

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

Accepted Answer

The CloudFormation template has a syntax error.. A CloudFormation template syntax error, such as a missing required property (e.g., 'Handler' or 'Runtime'), can cause the Lambda function resource to fail creation. The error message indicates the specific resource failed, and the absence of CloudWatch logs is expected because the function was never created. Option A is incorrect because code syntax errors do not prevent resource creation; they affect invocation. Option B is incorrect because the function not being invoked is a consequence, not the cause. Option C is incorrect because missing CloudWatch Logs permissions do not prevent creation; they only affect logging during invocation.

Answer

The Lambda function code has a syntax error that prevents creation.

Answer

The Lambda function was never invoked.

Answer

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

Question 2

A company runs a Node.js application on AWS Elastic Beanstalk. The application is experiencing high latency. The developer suspects the database queries are slow. Which step should the developer take first to diagnose the issue?

Accepted Answer

Enable enhanced health reporting and monitor CloudWatch metrics for database connection time.. The first step should be to enable enhanced health reporting and monitor CloudWatch metrics for database connection time. This provides visibility into the application's performance and helps identify if the database is indeed the bottleneck.

Answer

Migrate the database to Amazon DynamoDB for better performance.

Answer

Add database indexing to improve query performance.

Answer

Increase the instance size to improve performance.

Question 3

A developer is using AWS CloudFront to serve static content. Users in some geographic regions report slow load times. Which CloudFront feature can the developer use to reduce latency for these users?

Accepted Answer

Change the CloudFront price class to include all edge locations.. CloudFront's price class determines which edge locations are used to serve content. By default, CloudFront may use only a subset of edge locations (Price Class 100 or 200) to reduce costs, which can cause higher latency for users in regions not covered. Changing the price class to 'All Edge Locations' (Price Class All) ensures that CloudFront uses every global edge location, providing lower latency for all users. Option B is incorrect because creating multiple origins in different regions addresses origin distance, not edge location coverage. Option C is incorrect because S3 Transfer Acceleration is for speeding up uploads to S3, not for improving CloudFront content delivery. Option D is incorrect because Lambda@Edge can modify content at edge locations but does not expand the set of edge locations used.

Answer

Create multiple origins in different regions.

Answer

Enable S3 Transfer Acceleration on the origin S3 bucket.

Answer

Use Lambda@Edge to optimize content delivery.

Question 4

A developer is troubleshooting an AWS Lambda function that is triggered by an Amazon SQS queue. The function processes messages but occasionally fails. The failed messages are not being sent to the dead-letter queue (DLQ). What is the most likely reason?

Accepted Answer

The SQS queue's redrive policy is not configured.. For Lambda functions triggered by SQS, the dead-letter queue is configured on the SQS queue via its redrive policy, not on the Lambda function. If the redrive policy is missing or misconfigured, failed messages will not be moved to a DLQ even if the Lambda function has its own DLQ configured. The most likely reason is that the SQS queue's redrive policy is not configured.

Answer

The Lambda function's execution role does not have permission to send messages to the DLQ.

Answer

The Lambda function's reserved concurrency is set to 0.

Answer

The Lambda function does not have a dead-letter queue configured.

Question 5

A developer is using Amazon API Gateway with a Lambda authorizer to control access to APIs. The authorizer is failing with a 500 error. The Lambda function logs show 'User: arn:aws:iam::123456789012:role/MyLambdaRole is not authorized to perform: sts:AssumeRole'. What is the most likely cause?

Accepted Answer

The Lambda function's execution role does not have sts:AssumeRole permission for the target role.. The error message indicates that the Lambda function's execution role (MyLambdaRole) attempted to call sts:AssumeRole but was denied. This occurs when the Lambda function's code tries to assume another IAM role (e.g., to access a resource in another account or service) but the execution role lacks the necessary sts:AssumeRole permission for that target role. Option D correctly identifies this root cause. Option A is incorrect because an invalid policy from the authorizer would generate a different error (e.g., 403 or 401). Option B is incorrect because resource-based policies are for granting cross-account access to the Lambda function, not for assuming roles. Option C is incorrect because while API Gateway needs permission to invoke the Lambda function, a missing invoke permission would cause a different error (e.g., 500 with 'The API Gateway is not authorized to invoke the Lambda function'), not an sts:AssumeRole error.

Answer

The Lambda authorizer is not returning a valid policy.

Answer

The Lambda function's resource-based policy is missing.

Answer

The API Gateway does not have permission to invoke the Lambda function.

Question 6

Which TWO actions can help reduce latency for a web application hosted on EC2 instances behind an Application Load Balancer? (Select TWO.)

Accepted Answer

Use Amazon CloudFront as a content delivery network.. Option B is correct because Amazon CloudFront caches content at edge locations closer to end users, reducing round-trip time and offloading requests from the ALB and EC2 origin, which directly lowers latency for the web application. Option E is correct because ALBs natively support HTTP/2, and enabling it allows multiplexed streams over a single TCP connection, reducing connection overhead and improving page load latency for clients. Option A is not necessarily correct because a larger instance type increases compute capacity but does not inherently reduce network latency. Option C is incorrect because disabling keep-alive forces new TCP/TLS handshakes per request, increasing latency. Option D is incorrect because using multiple Availability Zones improves availability and fault tolerance, not latency.

Answer

Increase the EC2 instance size to a larger type.

Answer

Disable keep-alive connections on the ALB.

Answer

Use multiple Availability Zones for the ALB.

Question 7

Which TWO approaches can be used to optimize costs for an Amazon DynamoDB table with predictable read/write patterns? (Select TWO.)

Accepted Answer

Use provisioned capacity with auto scaling.. Option B is correct because provisioned capacity with auto scaling lets you set a target utilization and have Application Auto Scaling adjust read/write capacity units to match predictable traffic, so you pay only for the capacity you actually need rather than over-provisioning. Option D is correct because DAX is an in-memory cache for DynamoDB that serves eventually consistent reads from memory, reducing the number of read capacity units consumed on the table and lowering cost for read-heavy, predictable workloads. Option A is not correct because increasing read capacity units raises cost rather than optimizing it, and it addresses throttling, not cost efficiency. Option C is not correct because global tables add multi-region replication and incur extra write and storage costs, which is a resilience feature, not a cost optimization. Option E is not correct because on-demand capacity mode is designed for unpredictable or spiky workloads and typically costs more per request than well-tuned provisioned capacity for predictable patterns.

Answer

Increase the read capacity units to avoid throttling.

Answer

Use DynamoDB global tables for multi-region replication.

Answer

Use on-demand capacity mode.

Question 8

The developer invokes a Lambda function using the AWS CLI and gets the output shown. What is the most likely cause of the error?

Accepted Answer

The event payload does not contain the expected data.. When a Lambda function is invoked with a payload that does not match the handler's expected schema, the function raises a runtime error such as KeyError or TypeError, which surfaces as a function error in the CLI output. The most likely cause is a malformed or unexpected event payload rather than an infrastructure issue.

Answer

The Lambda function code has a syntax error.

Answer

The Lambda function's execution role lacks permissions.

Answer

The Lambda function timed out.

Question 9

A developer attached the IAM policy above to an IAM user. The user reports being unable to list objects in the bucket 'my-bucket' using the AWS CLI command 'aws s3 ls s3://my-bucket/'. What is the most likely reason?

Accepted Answer

The IAM policy does not include the s3:GetBucketLocation action.. The `aws s3 ls s3://my-bucket/` command requires the `s3:GetBucketLocation` permission to determine the bucket's region before listing its contents. Without this action, the CLI fails with an error like 'An error occurred (AccessDenied) when calling the GetBucketLocation operation', even if `s3:ListBucket` is granted. Option D correctly identifies this missing permission as the root cause.

Answer

The IAM policy does not allow the s3:GetObject action on the bucket.

Answer

The IAM policy resource for s3:ListBucket should include the bucket and objects.

Answer

The IAM policy is missing the s3:ListAllMyBuckets action.

Question 10

A developer is deploying a CloudFormation stack and sees the event above. What should the developer do to fix the error?

Accepted Answer

Change the runtime to a supported version like nodejs18.x.. The error indicates that the runtime (Node.js 12.x) used in the Lambda function is deprecated and no longer supported by AWS. To fix this, the developer must update the CloudFormation template to specify a supported runtime version, such as nodejs18.x, and redeploy the stack. Option C correctly identifies this solution. Option A is incorrect because the programming language itself is not the issue; the runtime version needs updating. Option B is incorrect because increasing the timeout does not address the unsupported runtime. Option D is incorrect because adding permissions does not resolve the runtime deprecation error.

Answer

Update the Lambda function code to use a different programming language.

Answer

Increase the Lambda function timeout in the template.

Answer

Add permissions to the Lambda function's execution role.

Question 11

A developer deployed a new version of a Lambda function that processes S3 events. After deployment, some S3 events are not being processed. The CloudWatch Logs show no errors. What is the most likely cause?

Accepted Answer

The S3 bucket's event notification still points to the old Lambda function.. After deploying a new version of a Lambda function, the S3 bucket's event notification configuration still references the Amazon Resource Name (ARN) of the old Lambda function version or the function without a qualifier. S3 event notifications are configured to invoke a specific Lambda function ARN, and if the ARN does not point to the new version (e.g., by using an alias or the $LATEST qualifier), events will continue to be sent to the old version, which may not be processing them. Since CloudWatch Logs show no errors, the old version is likely not being invoked or is not logging, confirming the mismatch.

Answer

The Lambda function has a syntax error.

Answer

The Lambda function alias is not pointing to the new version.

Answer

The S3 events are being throttled by Lambda.

Question 12

A developer is troubleshooting an EC2 instance that cannot connect to the internet. The instance has a public IP address and is in a public subnet with a route to an internet gateway. The security group allows all outbound traffic. What is the most likely cause?

Accepted Answer

The network ACL's outbound rules are blocking traffic.. Network ACLs are stateless and block traffic unless explicitly allowed. The security group allows all outbound traffic, but if the network ACL's outbound rules are too restrictive, traffic can be blocked. Option A is wrong because the subnet has a route to an internet gateway. Option B is wrong because the security group allows all outbound traffic. Option D is wrong because the instance has a public IP address.

Answer

The subnet's route table does not have a route to an internet gateway.

Answer

The security group's outbound rules are too restrictive.

Answer

The instance does not have a public IP address.

Question 13

A company's application running on Amazon ECS Fargate is experiencing high CPU utilization. The task definition has CPU set to 256 units. What should be done to improve performance?

Accepted Answer

Increase the CPU value in the task definition and redeploy the service.. Increasing CPU units in the task definition and redeploying the service will allocate more CPU to the tasks. Option A is wrong because horizontal scaling can help but the root cause is insufficient CPU per task. Option C is wrong because increasing memory does not affect CPU. Option D is wrong because changing the launch type changes billing but not CPU allocation.

Answer

Increase the desired count of tasks.

Answer

Increase the memory value in the task definition.

Answer

Switch to EC2 launch type.

Question 14

A developer is deploying a serverless application using AWS SAM. The deployment fails with the error 'Resource creation cancelled'. What is the most likely cause?

Accepted Answer

A resource in the stack failed to create.. The 'Resource creation cancelled' error in AWS SAM indicates that the CloudFormation stack creation was cancelled because one or more resources failed to create, triggering a rollback. Option A is incorrect because a malformed SAM template would produce a validation error, not 'Resource creation cancelled'. Option C is incorrect because a Lambda function timeout is a runtime issue, not a deployment error. Option D is incorrect because insufficient IAM permissions would result in an access denied error, not this specific cancellation message.

Answer

The SAM template is malformed.

Answer

The Lambda function code has a timeout.

Answer

The IAM role does not have sufficient permissions.

Question 15

A developer is using AWS CloudFormation to deploy a stack that includes an S3 bucket and a Lambda function. The stack fails with the error 'The following resource(s) failed to create: [MyBucket]'. What is the most likely cause?

Accepted Answer

The S3 bucket name is already taken.. The S3 bucket name is already taken. S3 bucket names must be globally unique across all AWS accounts and regions, so if the requested name already exists, CloudFormation fails to create the MyBucket resource with exactly this kind of 'failed to create' error. The other options do not fit: a VPC configuration issue would typically affect resources like Lambda or EC2 networking, not S3 bucket creation; a malformed bucket policy would usually fail during policy attachment or update rather than initial bucket creation; and invalid Lambda code would cause the Lambda resource to fail, not MyBucket.

Answer

The stack's VPC configuration is incorrect.

Answer

The S3 bucket policy is malformed.

Answer

The Lambda function code is invalid.