DVA-C02 Troubleshooting and Optimization Practice Test 6 — 15 Questions

Question 1

A company runs a serverless application using AWS Lambda and Amazon API Gateway. The application experiences intermittent 502 Bad Gateway errors. The Lambda function logs show no errors. What is the most likely cause?

Accepted Answer

The Lambda function execution time exceeds API Gateway's 29-second timeout.. The most likely cause is that the Lambda function execution time exceeds API Gateway's 29-second timeout. API Gateway has a hard limit of 29 seconds for integration responses, and if the Lambda function takes longer, API Gateway returns a 502 Bad Gateway error. Since the Lambda logs show no errors, the function is running successfully but timing out at the API Gateway level, not failing within Lambda itself.

Answer

The API Gateway account-level throttling limit is exceeded.

Answer

The Lambda function is throwing unhandled exceptions.

Answer

The API Gateway request payload exceeds 10 MB.

Question 2

A developer is troubleshooting a slow Amazon DynamoDB table. The table has a read capacity of 1000 RCU and a write capacity of 500 WCU. The application frequently reads the same item. Which TWO actions can improve read performance?

Accepted Answer

Implement DynamoDB Accelerator (DAX) for caching.. Option D is correct because DynamoDB Accelerator (DAX) is an in-memory cache that can reduce read latency for frequently accessed items from milliseconds to microseconds, offloading read traffic from the table and improving performance without requiring a capacity increase. Option E is correct because eventually consistent reads consume half the RCU of strongly consistent reads (0.5 RCU vs 1 RCU per 4 KB item) and return data faster, which is suitable when the application can tolerate slightly stale data for the same item.

Answer

Increase the read capacity units (RCU) to 2000.

Answer

Add a Global Secondary Index (GSI) on the frequently read attribute.

Answer

Decrease the write capacity units (WCU) to 250.

Question 3

A company uses AWS Step Functions to orchestrate a workflow. The workflow is failing with a 'States.ALL' error. Which THREE steps should the developer take to troubleshoot?

Accepted Answer

Review the state machine definition for syntax errors.. Check CloudWatch Logs for execution history (Option A). Check IAM permissions for the execution role (Option D). Check the state machine definition for invalid syntax (Option E). Option B is wrong because increasing memory does not fix state machine errors; Option C is wrong because X-Ray is not directly used for Step Functions errors.

Answer

Increase the memory allocated to the Lambda functions in the workflow.

Answer

Enable AWS X-Ray tracing on the state machine.

Question 4

A web application running on Amazon EC2 instances behind an Application Load Balancer (ALB) is experiencing intermittent 503 errors. Which TWO steps should be taken to diagnose the issue?

Accepted Answer

Check the CPU utilization of the EC2 instances.. Option B is correct because high CPU utilization on EC2 instances can cause them to become unresponsive or fail to respond to health checks within the ALB's configured timeout, leading to 503 errors. The ALB routes traffic only to healthy targets; if instances are overwhelmed, they may fail health checks or drop requests, resulting in a 503 response to clients.

Answer

Check the Route 53 health checks for the domain.

Answer

Check the security group rules for the ALB.

Answer

Check the EBS volume type of the EC2 instances.

Question 5

Refer to the exhibit. The developer runs the AWS CLI command to invoke a Lambda function. The output shows 'FunctionError': 'Unhandled'. What should the developer do to get more details about the error?

Accepted Answer

Decode the base64-encoded 'LogResult' field to view the log output.. The 'LogResult' field contains a base64-encoded log. Decoding it provides the error details. Option A is correct. Option B is wrong because 'FunctionError' indicates an error, not success. Option C is wrong because CloudWatch Logs is another option but not directly from the CLI output. Option D is wrong because X-Ray traces requests but not errors.

Answer

Re-invoke the function with a valid payload because the error is due to invalid input.

Answer

Enable AWS X-Ray tracing on the function.

Answer

Check the CloudWatch Logs for the function's log group.

Question 6

A developer is troubleshooting an AWS CloudFormation stack that failed to create. The error message says 'The following resource(s) failed to create: [MyEC2Instance]'. What is the first step the developer should take?

Accepted Answer

View the stack events in the CloudFormation console to see the specific error for the resource.. Option D is correct because when a CloudFormation stack fails to create, the error message only indicates which resource failed, not why. The first troubleshooting step is to view the stack events in the CloudFormation console, which provides detailed error messages for each resource, such as an API call failure, insufficient permissions, or a resource limit exceeded. This allows the developer to diagnose the root cause before making any changes.

Answer

Update the stack with a new template.

Answer

Delete the stack and try again.

Answer

Review the CloudFormation template for syntax errors.

Question 7

An application running on Amazon ECS with Fargate is unable to pull an image from Amazon ECR. The task definition uses the 'default' task execution role. What is the most likely cause?

Accepted Answer

The task execution role does not have permissions to pull from ECR.. Option D is correct because when using Amazon ECS with Fargate, the task execution role (not the task role) is responsible for pulling container images from Amazon ECR. The 'default' task execution role is created automatically but lacks the necessary permissions (e.g., ecr:GetDownloadUrlForLayer, ecr:BatchGetImage, and ecr:BatchCheckLayerAvailability) unless explicitly attached via an IAM policy. Since the question states the task definition uses the 'default' task execution role, the most likely cause is that this role does not have the required ECR permissions.

Answer

The task role does not have permissions to access ECR.

Answer

The ECS cluster does not have permissions to access ECR.

Answer

The ECS service role does not have permissions to access ECR.

Question 8

Refer to the exhibit. An IAM policy is attached to a user. The user tries to download an object from s3://my-bucket/secret/config.txt. What will happen?

Accepted Answer

The user is denied access because the Deny statement explicitly denies access to the 'secret/' prefix.. The Deny statement explicitly denies all s3 actions on the 'secret/' prefix. Deny statements override Allow statements. Option C is correct. Option A is wrong because the Deny is explicit. Option B is wrong because the Deny applies to the 'secret/' prefix. Option D is wrong because the Deny is not conditional.

Answer

The user is denied access only if the bucket policy also denies access.

Answer

The user can download the object because the Deny statement only applies to 's3:*' actions, not s3:GetObject.

Answer

The user can download the object because the Allow statement grants s3:GetObject on the bucket.

Question 9

Refer to the exhibit. A developer runs the AWS CLI command for an EC2 instance. The instance is in the 'running' state, but the application hosted on it is not reachable. What should the developer check first?

Accepted Answer

Check the security group rules for inbound traffic.. The application is unreachable despite the EC2 instance being in the 'running' state, which indicates the OS and instance services are operational. The most common cause for this scenario is that the security group's inbound rules are not allowing traffic on the application's port (e.g., HTTP/HTTPS on port 80/443). Security groups act as a virtual firewall at the instance level, and unless an inbound rule explicitly permits the traffic, it will be silently dropped, making the application unreachable.

Answer

Check the ELB health check settings.

Answer

Check the instance status checks in the EC2 console.

Answer

Verify the instance ID is correct.

Question 10

A developer is using Amazon S3 to host a static website. The website returns 403 Forbidden errors. The bucket policy allows public read access. What is the most likely cause?

Accepted Answer

The bucket's 'Block public access' settings are enabled.. The most likely cause is that the bucket's 'Block public access' settings are enabled. Even if the bucket policy explicitly grants public read access, S3's Block Public Access settings act as an overarching security override that denies all public requests, resulting in a 403 Forbidden error. These settings are enabled by default for new buckets and can be applied at the account or bucket level, making them a common pitfall.

Answer

The bucket has an ACL that denies read access.

Answer

The bucket policy does not include the 's3:GetObject' action.

Answer

The bucket policy is not correctly attached to the bucket.

Question 11

A developer is troubleshooting a slow Amazon RDS for MySQL database. The application experiences high latency on write operations. Which TWO actions can improve write performance?

Accepted Answer

Increase the allocated storage size to get better I/O performance.. Option B is correct because increasing the allocated storage size for an Amazon RDS for MySQL instance can improve I/O performance by providing a higher baseline IOPS rate. Larger volumes in RDS, especially those using General Purpose SSD (gp2/gp3), have higher throughput and IOPS limits, which directly reduces write latency under heavy load.

Answer

Add a read replica to offload read traffic.

Answer

Enable deletion protection.

Answer

Enable Multi-AZ deployment for high availability.

Question 12

A company uses AWS Lambda functions that are invoked by an Amazon S3 bucket notification. The function sometimes fails with a 'ResourceNotFoundException' for the S3 bucket. Which THREE steps should the developer take to resolve the issue?

Accepted Answer

Check the S3 bucket notification configuration for the correct Lambda function ARN.. Option B is correct because the 'ResourceNotFoundException' indicates that the Lambda function ARN specified in the S3 bucket notification configuration is incorrect or does not match the actual function ARN. S3 uses the notification configuration to invoke the Lambda function, and if the ARN is malformed, outdated, or points to a deleted function, S3 will throw this error. Verifying and correcting the ARN in the S3 event notification ensures S3 can successfully invoke the Lambda function.

Answer

Ensure the S3 bucket has versioning enabled.

Answer

Increase the Lambda function timeout.

Question 13

Refer to the exhibit. A CloudFormation stack creation failed. What is the most likely cause of the failure?

Accepted Answer

The IAM role's trust policy does not allow Lambda to assume the role.. The error message says the role cannot be assumed by Lambda. This is usually because the trust policy of the IAM role does not include 'lambda.amazonaws.com' as a trusted entity. Option D is correct. Option A is wrong because the error is about the role, not the code. Option B is wrong because the error mentions the role, not permissions. Option C is wrong because the error is not about resource conflict.

Answer

The Lambda function name conflicts with an existing function.

Answer

The Lambda function code has a syntax error.

Answer

The Lambda execution role does not have the required permissions to write to CloudWatch Logs.

Question 14

A developer is troubleshooting an AWS Lambda function that is timing out. The function processes S3 events and writes to DynamoDB. The average execution time is 5 seconds, but the function times out after 3 seconds. What is the most likely cause?

Accepted Answer

The Lambda function timeout is set to 3 seconds.. The lambda timeout setting defaults to 3 seconds. To fix, increase the timeout in the Lambda configuration to a value higher than the maximum expected execution time (e.g., 10 seconds). Option A is wrong because S3 event notifications are asynchronous and do not cause timeout. Option B is wrong because DynamoDB write capacity issues would cause throttling, not timeout. Option D is wrong because Lambda concurrency limits affect invocation throttling, not execution timeout.

Answer

The S3 bucket is not configured to send event notifications.

Answer

DynamoDB write capacity is insufficient.

Answer

The Lambda function concurrency limit is exceeded.

Question 15

A developer is using AWS CodeBuild to build a Java application. The build fails with 'OutOfMemoryError'. Which configuration change would most likely resolve this issue?

Accepted Answer

Increase the compute type to a larger instance size.. CodeBuild allows specifying compute type (e.g., BUILD_GENERAL1_MEDIUM) and memory. Increasing the compute type provides more memory. Option B is wrong because splitting into multiple projects adds complexity and may not resolve memory issues. Option C is wrong because enabling detailed logs does not increase memory. Option D is wrong because CodeBuild does not support custom AMIs.

Answer

Use a custom AMI with more memory.

Answer

Enable detailed CloudWatch logs for the build.

Answer

Split the build into multiple CodeBuild projects.