DVA-C02 Troubleshooting and Optimization Practice Test 17 — 15 Questions

Question 1

A developer is using Amazon DynamoDB with provisioned throughput. The application is receiving ProvisionedThroughputExceededException errors. What is the BEST way to handle this error?

Accepted Answer

Implement exponential backoff and retry in the application code.. The ProvisionedThroughputExceededException indicates that the application has exceeded the provisioned read/write capacity units for the DynamoDB table. The best practice to handle this error is to implement exponential backoff and retry logic in the application code, which progressively increases the wait time between retries to reduce request volume and allow the throttling to subside. This approach is recommended by AWS for handling throttling errors gracefully without manual intervention.

Answer

Contact AWS Support to increase the DynamoDB service limits.

Answer

Reduce the read and write capacity units.

Answer

Switch the table to on-demand capacity mode.

Question 2

An application uses an Amazon SQS queue to decouple microservices. The producer is sending messages, but the consumer is not processing them. The consumer is an Auto Scaling group of EC2 instances. The SQS queue's ApproximateNumberOfMessagesVisible metric is increasing. What is the MOST likely cause?

Accepted Answer

The consumer instances are not polling the SQS queue.. If the ApproximateNumberOfMessagesVisible metric keeps rising while the consumer Auto Scaling group is running, the most likely cause is that the consumer instances are not polling the queue at all. Without active long-polling ReceiveMessage calls, messages accumulate and are never processed, even though the queue and permissions may be fine. This is the most direct explanation for a growing visible-message count with no consumption.

Answer

The SQS queue policy denies access to the consumer.

Answer

The visibility timeout is set too low.

Answer

The SQS queue has a dead-letter queue configured.

Question 3

A developer is deploying a new version of an AWS Lambda function using the AWS CLI. The deployment fails with a 'ResourceConflictException' error. What is the MOST likely cause?

Accepted Answer

Another deployment is currently in progress for the same Lambda function.. The 'ResourceConflictException' error in AWS Lambda occurs when you attempt to update a Lambda function while another update operation is already in progress. Lambda enforces a single in-flight update per function to prevent race conditions and ensure state consistency. The AWS CLI command (e.g., update-function-code) will fail immediately if a previous deployment has not completed, even if the previous deployment was triggered by the same or a different client.

Answer

The Lambda function code exceeds the maximum allowed size.

Answer

The Lambda function has an alias that conflicts with the version number.

Answer

The IAM role associated with the Lambda function does not have sufficient permissions.

Question 4

A developer is using Amazon CloudFront to serve static content from an S3 bucket. Users are reporting that they see outdated content. The CloudFront distribution has a default TTL of 24 hours. What is the MOST efficient way to serve updated content immediately?

Accepted Answer

Create a CloudFront invalidation for the updated objects.. Creating a CloudFront invalidation for the updated objects is the most efficient way to immediately serve updated content because it forces CloudFront to fetch the latest version from the origin, bypassing the cached copies. This method is targeted and does not affect other cached objects, making it ideal for urgent updates.

Answer

Disable and re-enable the CloudFront distribution.

Answer

Update the object key in the S3 bucket.

Answer

Change the default TTL to 0.

Question 5

A developer is troubleshooting an AWS Lambda function that is timing out. The function has a timeout of 5 seconds and is configured with 128 MB of memory. Which TWO of the following are effective ways to resolve the timeout?

Accepted Answer

Increase the memory allocation to 512 MB.. Increasing memory allocation in AWS Lambda proportionally increases CPU and network throughput, which can reduce execution time and prevent timeouts. With 128 MB, the function may be CPU-bound; raising it to 512 MB provides more compute resources, often resolving timeout issues without code changes.

Answer

Decrease the memory allocation to 64 MB.

Answer

Deploy the function inside a VPC.

Answer

Increase the function timeout to 10 seconds.

Question 6

A company has a REST API deployed on Amazon API Gateway with a Lambda integration. The API is experiencing high latency. Which TWO actions would help diagnose the issue?

Accepted Answer

Use AWS X-Ray to trace requests.. Option A is correct because AWS X-Ray traces the full request path through API Gateway, the Lambda integration, and downstream calls, exposing where latency is introduced (e.g., Lambda cold starts, slow downstream calls) via trace segments and subsegments. Option B is correct because enabling detailed CloudWatch Logs (execution logging and access logging) for the API Gateway stage captures per-request latency metrics such as integrationLatency and responseLatency, helping pinpoint whether the delay is in API Gateway or the Lambda backend. Option C is not a diagnostic action; increasing Lambda memory changes CPU allocation and could improve performance but does not help identify the root cause of latency. Option D is not a diagnostic step and changing the integration type alters architecture rather than measuring where latency occurs. Option E is also a remediation/architecture change (caching and edge termination) rather than a way to diagnose the source of the high latency.

Answer

Increase the Lambda function memory.

Answer

Change the API integration type from Lambda to HTTP.

Answer

Add Amazon CloudFront in front of API Gateway.

Question 7

A developer is using an Amazon SQS queue with a Lambda function as a consumer. Messages are being sent to the queue but the Lambda function is not processing them. Which THREE of the following are possible causes?

Accepted Answer

The SQS queue policy denies access to the Lambda function.. The SQS queue policy is a resource-based policy that controls which principals (like Lambda's execution role) can perform actions on the queue. If the policy explicitly denies the Lambda function's access, the function will not be able to poll or delete messages from the queue, even if its own execution role grants those permissions.

Answer

The SQS queue has a dead-letter queue configured.

Answer

The SQS queue has a rate limit that prevents Lambda from polling.

Question 8

A developer is troubleshooting an AWS Lambda function that times out when processing large files from Amazon S3. The function has a 15-minute timeout and 512 MB memory. What should the developer do to resolve this issue?

Accepted Answer

Increase the Lambda function memory to 3008 MB.. Increasing the Lambda function memory to 3008 MB is correct because Lambda allocates CPU proportionally to memory, and more CPU reduces processing time for CPU-bound tasks like file parsing. The 15-minute timeout is already the maximum, so the issue is insufficient compute resources, not timeout duration. With 512 MB, the function lacks the CPU throughput to process large files within the timeout, so boosting memory (and thus CPU) directly addresses the root cause.

Answer

Use Amazon S3 batch operations to split the files before processing.

Answer

Add an S3 Event Notification to trigger the function asynchronously.

Answer

Reduce the Lambda timeout to 5 minutes to force faster processing.

Question 9

A developer notices that an Amazon RDS for MySQL DB instance's CPU utilization is consistently above 90% during peak hours. Which AWS service can the developer use to analyze the database queries and identify the root cause?

Accepted Answer

Amazon RDS Performance Insights. Amazon RDS Performance Insights is the correct service for analyzing database queries and identifying the root cause of high CPU utilization. Performance Insights provides a database performance analysis feature that offers a visual dashboard and query-level metrics, enabling developers to pinpoint resource-intensive queries. AWS X-Ray is used for tracing application requests, not database queries. CloudWatch Logs is for log data storage and monitoring, not query-level analysis. Trusted Advisor provides cost and security recommendations, not database performance insights. Therefore, Performance Insights is the appropriate tool for this scenario.

Answer

AWS X-Ray

Answer

Amazon CloudWatch Logs

Answer

AWS Trusted Advisor

Question 10

A developer is debugging an AWS Lambda function that is invoked by an Amazon S3 bucket notification. The function fails with an 'AccessDenied' error when trying to read an object from the same bucket. What should the developer check first?

Accepted Answer

Review the Lambda function's execution role for s3:GetObject permission.. The developer should first review the Lambda function's execution role for s3:GetObject permission. The 'AccessDenied' error indicates the function lacks permission to read the object. The execution role must have an IAM policy granting s3:GetObject on the bucket or object. This is the most direct cause.

Answer

Check if S3 bucket versioning is enabled.

Answer

Verify that the S3 bucket uses server-side encryption with AWS KMS.

Answer

Ensure the S3 bucket is not blocked by S3 Block Public Access.

Question 11

An application running on Amazon EC2 instances behind an Application Load Balancer (ALB) is experiencing increased latency. The developer suspects the ALB is the bottleneck. How can the developer confirm this using CloudWatch metrics?

Accepted Answer

Monitor the TargetResponseTime metric and compare it to the client's perspective.. To determine if the ALB or the backend targets are causing the latency, the developer should monitor the 'TargetResponseTime' metric. This metric measures the time elapsed (in seconds) from when the request leaves the ALB until a response from the target is received. If 'TargetResponseTime' is low but the client-side latency is high, the bottleneck lies within the ALB itself or the network. If 'TargetResponseTime' is high, the bottleneck is the backend EC2 instances. 'SurgeQueueLength' is a Classic Load Balancer metric and is not available on ALBs.

Answer

Monitor the HealthyHostCount metric and ensure it is equal to the number of instances.

Answer

Monitor the SurgeQueueLength metric and look for sustained high values.

Answer

Monitor the RequestCount metric and check if it exceeds the ALB's limit.

Question 12

A developer deploys a new version of an AWS Lambda function using the AWS CLI. After deployment, the function returns stale results. What is the most likely cause?

Accepted Answer

The Lambda function alias is still pointing to the previous version.. When a developer deploys a new version of a Lambda function using the AWS CLI without updating the function alias, the alias continues to point to the previous version. Invoking the function via the alias (e.g., via an API Gateway endpoint or a CloudFront origin) will execute the old code, returning stale results. The `$LATEST` version is updated, but unless the alias is repointed, it does not automatically use the new code.

Answer

The function's environment variables are cached and not updated.

Answer

The Amazon CloudFront distribution is caching the old response.

Answer

The Lambda function's code is cached by the Lambda service.

Question 13

A company's application uses Amazon DynamoDB as its database. The application reads the same item multiple times per second and occasionally sees stale data. The DynamoDB table uses the default eventually consistent reads. What should the developer change to ensure strongly consistent reads?

Accepted Answer

Set the ConsistentRead parameter to true in the GetItem call.. DynamoDB's default read consistency model is eventually consistent, which can return stale data if an item is updated shortly before the read. By setting the `ConsistentRead` parameter to `true` in the `GetItem` call, the developer forces a strongly consistent read, ensuring the response reflects the most recent write. This directly addresses the stale data issue without changing throughput or adding caching.

Answer

Increase the read capacity units of the table.

Answer

Use DynamoDB Accelerator (DAX) to cache the item.

Answer

Use DynamoDB transactions for all read operations.

Question 14

A developer optimized an Amazon S3 bucket for high request rates. The bucket receives over 5,000 PUT requests per second. Recently, some requests are failing with a 503 Slow Down error. What is the most likely cause and how should the developer fix it?

Accepted Answer

Add a random prefix to the object keys to distribute across partitions.. S3 returns 503 when request rates exceed partition limits. Prefix randomization spreads requests across partitions. Option A is wrong because 503 is not due to permissions. Option B is wrong because 503 is not a quota limit exceeded error (that would be 400). Option C is wrong because multipart upload is for large objects, not rate limits.

Answer

Use multipart upload for all objects to improve throughput.

Answer

The request rate exceeds the account-level PUT quota; request a quota increase.

Answer

The bucket policy is too permissive; restrict access to prevent abuse.

Question 15

A developer invoked a Lambda function and saw the above output. What is the root cause of the error?

Accepted Answer

The function code expects a property that is missing from the event payload.. The correct answer is B: the function code expects a property that is missing from the event payload. In Lambda, when the handler accesses a key on the parsed event object (e.g., event['detail'] or event.detail) that does not exist, the runtime raises a KeyError or TypeError, which surfaces as an invocation error in the response. This is a data-shape mismatch between what the code reads and what the caller sent, not an infrastructure or configuration failure. Option A is wrong because payload access is not gated by IAM permissions; the event is always delivered to the handler. Option C is wrong because an incorrect handler name produces a Runtime.HandlerNotFound or 'handler does not exist' error before any code runs. Option D is wrong because a timeout returns Task timed out after X seconds rather than a missing-property error.

Answer

The Lambda function lacks permission to access the event payload.

Answer

The Lambda function's handler name is incorrect.

Answer

The Lambda function timed out.