DVA-C02 Troubleshooting and Optimization Practice Test 3 — 15 Questions

Question 1

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?

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

Accepted Answer

Check the security group rules for inbound traffic.. When an EC2 instance is in the 'running' state but the application is unreachable, the most common initial cause is that the Security Group associated with the instance does not allow inbound traffic on the application's port (e.g., port 80 or 443). Security groups act as stateful firewalls at the instance level, and by default, they block all inbound traffic unless explicitly allowed.

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 2

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.. To improve write performance on an Amazon RDS for MySQL database, you can:
1. Increase the allocated storage size (Option B): For General Purpose SSD (gp2) volumes, IOPS are directly tied to the storage size (3 IOPS per GiB). Increasing the storage size increases the baseline IOPS and throughput, which helps resolve I/O bottlenecks on writes.
2. Increase the DB instance class (Option D): A larger DB instance class provides more CPU, memory, and dedicated EBS bandwidth, allowing the database to process more write transactions and handle higher network throughput.

Other options are incorrect:
- Option A (Read replicas) only offloads read traffic and does not improve write performance.
- Option C (Deletion protection) is a security feature to prevent accidental deletion and has no impact on performance.
- Option E (Multi-AZ) actually increases write latency slightly because writes must be synchronously replicated to the standby replica before being acknowledged.

Answer

Add a read replica to offload read traffic.

Answer

Enable deletion protection.

Answer

Enable Multi-AZ deployment for high availability.

Question 3

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.. The 'ResourceNotFoundException' for the S3 bucket indicates that the Lambda function cannot locate or access the S3 bucket when invoked via notification. This can occur due to three reasons: (B) The S3 notification configuration has an incorrect Lambda function ARN, so S3 cannot find the function to invoke it, resulting in a ResourceNotFoundException. (C) The Lambda execution role lacks permissions to read from the S3 bucket; although a permission issue typically causes AccessDeniedException, in some SDKs or scenarios it may manifest as ResourceNotFoundException when attempting to access the bucket. (E) The S3 bucket no longer exists or is in a different region; Lambda functions must be in the same region as the S3 bucket to access it without cross-region configurations. Options A (enabling versioning) and D (increasing timeout) do not address the bucket not found error.

Answer

Ensure the S3 bucket has versioning enabled.

Answer

Increase the Lambda function timeout.

Question 4

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 CloudFormation stack creation failed because the IAM role specified for the Lambda function does not have a trust policy that allows the Lambda service to assume it. Without a trust policy that includes 'lambda.amazonaws.com' as a trusted entity, Lambda cannot assume the role, causing the stack creation to fail. Option A correctly identifies this issue. Option B is incorrect because the error is about role assumption, not a naming conflict. Option C is incorrect because the error occurs before the function code is executed. Option D is incorrect because the error is not about permissions to write to CloudWatch Logs; it is about the inability to assume the role itself.

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 5

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 6

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 configuring the compute type (e.g., BUILD_GENERAL1_MEDIUM, BUILD_GENERAL1_LARGE) which determines the memory and CPU available. An 'OutOfMemoryError' indicates insufficient memory, so increasing the compute type to a larger instance size provides more memory and resolves the issue. Option A is incorrect because CodeBuild does not support custom AMIs; it uses managed container images. Option B is incorrect because enabling detailed CloudWatch logs only increases logging, not memory. Option D is incorrect because splitting the build adds complexity and does not address the memory shortage in the current build.

Answer

Use a custom AMI with more memory.

Answer

Enable detailed CloudWatch logs for the build.

Answer

Split the build into multiple CodeBuild projects.

Question 7

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?

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 8

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 to diagnose slow database queries is to monitor and gather data. Enabling enhanced health reporting in Elastic Beanstalk and using CloudWatch metrics allows the developer to analyze database connection times and identify performance bottlenecks (option B). Option A is incorrect because migrating to DynamoDB is a solution, not a diagnostic step, and may not address the root cause. Option C is incorrect because adding database indexing should be based on query analysis, not as a first step without diagnostics. Option D is incorrect because increasing instance size addresses compute resources, not database query performance directly, and should only be considered after identifying 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 9

A developer is using Amazon S3 Transfer Acceleration to upload a large file. The upload is slower than expected. Which metric should the developer check to determine if Transfer Acceleration is providing a benefit?

Accepted Answer

CloudWatch metric 'Requests' for the S3 bucket.. The Amazon S3 Transfer Acceleration Speed Comparison tool compares upload speeds to Amazon S3 with and without using S3 Transfer Acceleration. It uses multipart uploads to transfer files from your browser to different AWS regions, showing you the percentage improvement in speed when using Transfer Acceleration.

Answer

CloudWatch metric 'BytesDownloaded' for the S3 bucket.

Answer

CloudWatch metric 'TotalRequestLatency' for the S3 bucket.

Answer

CloudWatch metric 'FirstByteLatency' for the S3 bucket.

Question 10

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 11

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 12

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.. Enabling HTTP/2 on the ALB reduces latency by allowing multiplexed streams over a single connection, reducing head-of-line blocking. Using Amazon CloudFront as a CDN caches content at edge locations closer to users, lowering latency. Option A (increasing instance size) may not address network or I/O bottlenecks. Option C (disabling keep-alive) forces new TCP connections for each request, increasing latency. Option D (multiple Availability Zones) improves fault tolerance and availability, 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 13

A developer is investigating why an AWS Lambda function that processes Kinesis records is experiencing high latency. Which THREE factors could contribute to this? (Select THREE.)

Accepted Answer

Low number of shards in the Kinesis stream.. Low number of shards in the Kinesis stream (A) reduces the stream's throughput, leading to throttling and retries that increase latency. High batch size in the event source mapping (B) causes each Lambda invocation to process more records, increasing execution time. Insufficient memory allocated to the Lambda function (E) slows CPU performance and execution speed. High concurrency limit (C) generally reduces latency by allowing more parallel processing. Lambda@Edge (D) is used with CloudFront, not for Kinesis streams, and is irrelevant to this latency issue.

Answer

High concurrency limit for the Lambda function.

Answer

Using Lambda@Edge to process the records.

Question 14

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.. The error 'Cannot read property 'x' of undefined' is a runtime error indicating that the Lambda function's code tried to access a property on an undefined object. This most commonly occurs when the event payload does not have the expected structure or missing required fields. Option C is correct because the payload likely lacks the expected property, causing the code to fail. Option A is incorrect because a syntax error would prevent the function from being invoked, while this error occurs during execution. Option B is incorrect because execution role permissions affect access to AWS services, not code-level property access. Option D is incorrect because a timeout would manifest as a different error (e.g., 'Task timed out').

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 15

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.