DVA-C02 Troubleshooting and Optimization Practice Test 9 — 15 Questions

Question 1

Which TWO actions should a developer take to optimize cost and performance for a Lambda function that processes real-time streaming data from Amazon Kinesis? (Choose 2.)

Accepted Answer

Enable the parallelization factor to process multiple batches concurrently per shard.. Increasing batch size reduces the number of Lambda invocations by processing more records per invocation, which lowers cost. Enabling the parallelization factor allows multiple concurrent batches per shard, improving throughput and reducing processing latency. Together, these optimize both cost and performance for Kinesis-triggered Lambda functions.

Answer

Enable provisioned concurrency to reduce cold starts.

Answer

Increase the Lambda function memory to improve processing speed.

Answer

Use a larger Kinesis shard count.

Question 2

A developer is troubleshooting an EC2 instance that is unreachable via SSH. The instance is in a public subnet with a security group that allows inbound SSH from 0.0.0.0/0. Which THREE are possible causes? (Choose 3.)

Accepted Answer

The network ACL associated with the subnet is blocking inbound SSH.. Network ACLs can block traffic even if security group allows. The instance may not have a public IP. The IAM role doesn't affect SSH access. The key pair is used for authentication, not connectivity. The instance may be stopped.

Answer

The SSH key pair used to launch the instance is incorrect.

Answer

The instance does not have an IAM role with the necessary permissions.

Question 3

Which TWO practices help optimize costs in Amazon DynamoDB? (Choose 2.)

Accepted Answer

Use Auto Scaling to adjust read/wapacity based on traffic.. DynamoDB Auto Scaling automatically adjusts provisioned read and write capacity based on actual traffic patterns, preventing over-provisioning and reducing costs during low-demand periods. Option E is correct because on-demand capacity mode charges per request, making it cost-effective for unpredictable workloads where capacity planning is difficult, avoiding the cost of idle provisioned capacity.

Answer

Purchase reserved capacity for all tables regardless of usage.

Answer

Create multiple Global Secondary Indexes for query flexibility.

Answer

Enable DAX (DynamoDB Accelerator) for all tables.

Question 4

A developer attached the IAM policy above to an IAM role used by an EC2 instance. The instance is in a VPC with CIDR 10.0.0.0/16, but it cannot access objects in the S3 bucket 'example-bucket'. What is the MOST likely reason?

Accepted Answer

The condition should use 'aws:VpcSourceIp' instead of 'aws:SourceIp'.. The condition uses 'aws:SourceIp', but EC2 instances in a VPC have private IPs. For S3, the source IP that AWS sees is the public IP (if traffic goes through internet gateway) or the VPC endpoint's private IP. If the bucket policy uses 'aws:SourceIp', it compares against the source IP of the request, which for EC2 instances without a VPC endpoint is the instance's public IP (if any) or the NAT gateway's IP, not the private IP. The condition should use 'aws:VpcSourceIp' if using a VPC endpoint, or the policy should not rely on source IP from private ranges.

Answer

The policy does not allow 's3:ListBucket' action.

Answer

The IAM role does not have a trust policy.

Answer

The S3 bucket is in a different region than the EC2 instance.

Question 5

A developer notices that the Lambda function 'my-function' is not generating any logs in CloudWatch, although the function is invoked successfully. The developer runs the command above. What is the MOST likely cause?

Accepted Answer

The Lambda function's execution role is missing the 'logs:CreateLogStream' and 'logs:PutLogEvents' permissions.. The log group exists but has 0 stored bytes, meaning no log streams have been created. This typically indicates that the Lambda function's execution role does not have permissions to create log streams and put log events. The function runs but fails silently to write logs.

Answer

The log group retention policy is set to 0 days.

Answer

The Lambda function is configured to log to a custom log group.

Answer

The Lambda function has reserved concurrency set to 0.

Question 6

A developer tries to create a CloudFormation stack using the template above, but it fails with 'The bucket you tried to create already exists'. The developer has already deleted the bucket from the AWS Management Console. What is the MOST likely reason for the failure?

Accepted Answer

The bucket name is still globally reserved after deletion.. Even after deletion, the bucket name may still be in a 'pending deletion' state or may have been taken by another AWS account. S3 bucket names are globally unique. If the name is still reserved (e.g., recently deleted), you cannot recreate it immediately. The developer should use a different bucket name.

Answer

The CloudFormation template uses an incorrect intrinsic function.

Answer

Bucket versioning must be Disabled initially.

Answer

The developer does not have permission to create buckets in that region.

Question 7

A company runs a Node.js application on Amazon EC2 instances behind an Application Load Balancer (ALB). Users report intermittent 503 errors. The ALB target group health checks are failing. The developer checks the EC2 instance logs and sees no application errors. What is the MOST likely cause?

Accepted Answer

The security group for the EC2 instances does not allow inbound traffic from the ALB.. When an ALB target group's health checks fail, the ALB will return HTTP 503 (Service Unavailable) errors to clients because there are no healthy targets to route traffic to. If the developer checks the EC2 instance logs and sees no application errors (or no connection attempts at all), it indicates that the health check requests are not even reaching the application. This is typically caused by a security group misconfiguration where the EC2 instances' security group does not allow inbound traffic from the ALB's security group. Option C is incorrect because if the application returned a 5xx status code, the request would have reached the Node.js application, and the error or access attempt would be recorded in the logs.

Answer

The health check path is set to '/' but the application serves on a different path.

Answer

The EC2 instances are running out of memory.

Answer

The health check path returns a 5xx status code due to a missing dependency.

Question 8

A developer is troubleshooting a slow Amazon RDS MySQL database query. The query is frequently executed and takes 5 seconds to complete. Which AWS service should the developer use to analyze the query performance?

Accepted Answer

Amazon RDS Performance Insights. Amazon RDS Performance Insights is the correct service for analyzing Amazon RDS database query performance. It provides a visual dashboard to analyze database load, identify top queries by various metrics like latency, and pinpoint performance bottlenecks. AWS CloudTrail (Option A) records API activity, not database query details. Amazon CloudWatch Logs (Option C) collects log data but does not offer query-level performance analysis. AWS X-Ray (Option D) is used for tracing requests in distributed applications, not for database query analysis.

Answer

AWS CloudTrail

Answer

Amazon CloudWatch Logs

Answer

AWS X-Ray

Question 9

A developer deployed a new version of an AWS Lambda function using the AWS CLI update-function-code command. The function uses environment variables to store database credentials. After the update, the function returns errors indicating it cannot connect to the database. What is the MOST likely cause?

Accepted Answer

The database credentials are encrypted but the function cannot decrypt them.. The update-function-code command only updates the function code, not the function configuration. Environment variables are preserved from the existing configuration, so option C is incorrect. The most likely cause is option B: the database credentials are encrypted but the function cannot decrypt them. This could happen if the new code accidentally altered the decryption logic or if the function's execution role lacks permissions to use the required KMS key, leading to connection errors.

Answer

The function ARN changed after the update.

Answer

The environment variables were not set in the new version.

Answer

The function's IAM role was changed during the update.

Question 10

A company uses Amazon API Gateway with a Lambda integration. The API returns a 502 Bad Gateway error for some requests. The Lambda function writes logs to CloudWatch. Which steps should a developer take to troubleshoot this issue? (Select the BEST combination.)

Accepted Answer

Increase the Lambda function timeout and review the CloudWatch logs for errors.. Increasing the Lambda function timeout can resolve timeouts that cause 502 errors, and reviewing CloudWatch logs helps identify any errors in the Lambda function. Option A is wrong because enabling detailed metrics helps with monitoring but does not directly troubleshoot the 502 error. Option B is wrong because IAM permissions issues would result in a 403 Forbidden error, not a 502. Option C is wrong because API Gateway throttling returns a 429 Too Many Requests error, not a 502.

Answer

Enable API Gateway detailed metrics and create a dashboard.

Answer

Verify the IAM role permissions for API Gateway to invoke Lambda.

Answer

Check the API Gateway throttling settings and request limit.

Question 11

A developer is deploying a new version of an application to Amazon ECS using the Fargate launch type. The task fails to start and the error message indicates that the task cannot pull the container image from Amazon ECR. What is the MOST likely cause?

Accepted Answer

The task execution role lacks permissions to pull from ECR.. The error message indicates a failure to pull the container image from Amazon ECR. The task execution role must have permissions such as ecr:GetDownloadUrlForLayer and ecr:BatchGetImage to pull images. Option A is wrong because the task definition family name does not affect image pulling. Option C is wrong because Fargate does not use host port mapping; container port mapping is handled automatically. Option D is wrong because insufficient CPU or memory typically results in a different error (e.g., task stuck in provisioning), not an image pull failure.

Answer

The task definition family name is incorrect.

Answer

The container port is not mapped to a host port.

Answer

The CPU or memory limits are too low for the container.

Question 12

A company is using Amazon DynamoDB with on-demand capacity. A developer notices that write requests are being throttled during peak hours. What is the MOST effective way to resolve this issue?

Accepted Answer

Review the partition key design and consider adding a suffix to distribute writes.. On-demand capacity automatically scales to handle traffic, but if the traffic exceeds the previous peak by a large margin, throttling can still occur due to partition-level limits. Reviewing the partition key design and adding a suffix can help distribute writes across multiple partitions, reducing hot partitions and mitigating throttling. Option A is wrong because switching to provisioned capacity with auto-scaling would require managing capacity and on-demand already scales automatically. Option B is wrong because there are no write capacity units in on-demand mode; throttling is related to partition throughput. Option D is wrong because increasing read capacity does not affect write throttling.

Answer

Switch to provisioned capacity mode with auto-scaling.

Answer

Increase the write capacity units.

Answer

Increase the read capacity units.

Question 13

A developer is troubleshooting an AWS CloudFormation stack creation failure. The stack creation failed with the error: 'Resource creation cancelled'. What does this error typically indicate?

Accepted Answer

Another resource in the stack failed, causing a rollback.. 'Resource creation cancelled' means a different resource in the stack failed, causing rollback. Option A is wrong because insufficient IAM permissions would give an access denied error. Option C is wrong because the error is not about template validation. Option D is wrong because an unsupported resource type would cause a different error, not 'Resource creation cancelled'.

Answer

The IAM user does not have permission to create the resource.

Answer

The template has a syntax error.

Answer

The resource type is not supported by CloudFormation.

Question 14

A developer is optimizing an AWS Lambda function that processes streaming data from Amazon Kinesis. The function is CPU-bound. Which TWO actions should the developer take to improve performance?

Accepted Answer

Rewrite the function in a compiled language like Go.. Using a compiled language like Go can reduce CPU execution time compared to interpreted languages. Option C is correct because increasing memory allocation also increases the CPU resources allocated to the Lambda function, which helps CPU-bound tasks. Option B is wrong because reserved concurrency only affects the number of concurrent invocations, not per-invocation performance. Option D is wrong because increasing shard count does not improve Lambda function performance. Option E is wrong because AWS Lambda does not support GPU acceleration.

Answer

Increase the function's reserved concurrency.

Answer

Increase the Kinesis stream's shard count.

Answer

Enable GPU acceleration for the function.

Question 15

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.