DVA-C02 Troubleshooting and Optimization Practice Test 10 — 15 Questions

Question 1

An application running on Amazon EC2 generates logs that need to be streamed to Amazon CloudWatch Logs. The developer installs and configures the CloudWatch agent. However, logs are not appearing in the log group. What is the most likely cause?

Accepted Answer

The EC2 instance does not have an IAM role with CloudWatch Logs write permissions.. The CloudWatch agent requires an IAM role with permissions to write logs. Without the proper permissions, the agent cannot send logs. Option A is correct. Option B is wrong because the agent can be installed on EC2. Option C is wrong because the log group is created automatically if not existing. Option D is wrong because the agent is configured via a config file, not the console.

Answer

The CloudWatch agent cannot be installed on Amazon Linux 2.

Answer

The CloudWatch agent must be configured from the AWS Management Console.

Answer

The log group must be created manually before the agent can send logs.

Question 2

A developer has an AWS Lambda function that processes messages from an Amazon SQS queue. The function is experiencing high invocation errors. The developer sees that the function's reserved concurrency is set to 0. What is the impact?

Accepted Answer

The function is not receiving any invocations because it has no concurrency available.. Reserved concurrency of 0 means the function cannot scale, so no invocations occur. This causes all messages to stay in the queue or go to DLQ. Option B is correct. Option A is wrong because throttling is not the main issue. Option C is wrong because the function never runs. Option D is wrong because concurrency limit is 0.

Answer

The function's memory is insufficient, causing out-of-memory errors.

Answer

The function is throttled due to high request volume.

Answer

The function's code has an error causing it to fail.

Question 3

A developer is troubleshooting an AWS Elastic Beanstalk environment that is failing health checks. The environment runs a web application on Tomcat. The developer checks the logs and finds no errors. What is the most likely cause of the health check failure?

Accepted Answer

The application's health check URL is returning a non-200 status code.. The most likely cause is that the application's health check URL is returning a non-200 status code. Elastic Beanstalk uses the load balancer to perform health checks against a configurable path (default: /). If the application responds with any status other than 200 OK, the load balancer marks the instance as unhealthy, even if the application logs show no errors. This is a common misconfiguration where the health check endpoint is not implemented or returns an unexpected status.

Answer

The security group for the instances does not allow traffic from the load balancer.

Answer

The application is throwing exceptions that are not logged.

Answer

The application is listening on a port other than 80.

Question 4

A developer is using Amazon DynamoDB for a new application. The developer wants to reduce read latency. Which design pattern should the developer use?

Accepted Answer

Use DynamoDB Accelerator (DAX) as a cache for frequently read items.. DynamoDB Accelerator (DAX) is an in-memory cache designed specifically for DynamoDB, providing microsecond read latency for frequently accessed items. By caching read-heavy workloads, DAX offloads requests from the DynamoDB table, reducing read latency without requiring application-level caching logic. This directly addresses the developer's goal of reducing read latency.

Answer

Create a global secondary index (GSI) for the table.

Answer

Increase the provisioned read capacity units (RCUs) for the table.

Answer

Use DynamoDB Global Tables to replicate data to multiple regions.

Question 5

A developer is deploying a serverless application using AWS CloudFormation. The stack creation fails with the error 'CREATE_FAILED: The following resource(s) failed to create: [MyLambdaFunction]'. The developer checks the CloudFormation events and sees 'Resource creation cancelled'. What is the most likely cause?

Accepted Answer

Another resource in the stack failed, triggering a rollback and cancelling the Lambda creation.. CloudFormation cancels resource creation if a previous resource fails and the stack is set to roll back on failure. The Lambda function creation may have been cancelled due to another resource failure. Option A is correct. Option B is wrong because the error is not specific to IAM. Option C is wrong because the Lambda function creation was cancelled, not failed due to timeout. Option D is wrong because the error does not mention throttling.

Answer

The Lambda function code is too large and exceeds the deployment limit.

Answer

The Lambda function creation timed out due to a network issue.

Answer

The Lambda function's execution role is missing permissions.

Question 6

A developer is using Amazon API Gateway with a Lambda integration. The API returns a 502 Bad Gateway error. The developer checks the Lambda function logs and finds no invocations. What is the most likely cause?

Accepted Answer

The API Gateway does not have permission to invoke the Lambda function.. A 502 Bad Gateway error from API Gateway with Lambda integration typically indicates that the Lambda function either returned an invalid response or was not invoked at all. Since the Lambda logs show no invocations, the most likely cause is that API Gateway lacks the necessary resource-based policy permission to invoke the Lambda function. Without this permission, API Gateway cannot trigger the function, resulting in a 502 error without any invocation record.

Answer

The Lambda function is returning a non-JSON response.

Answer

The Lambda function is timing out due to a long-running operation.

Answer

The Lambda function's memory is insufficient, causing it to crash.

Question 7

A developer is using Amazon S3 to host a static website. The developer updates the files, but users still see the old version. What is the most likely cause?

Accepted Answer

The browser is caching the old files.. S3 static website hosting serves objects directly. If users see old content, it's likely due to browser caching. Option A is correct. Option B is wrong because S3 does not cache content at the bucket level. Option C is wrong because CloudFront is not mentioned. Option D is wrong because S3 static hosting serves files from the bucket.

Answer

The S3 bucket has server-side caching enabled.

Answer

The files are being served from a CloudFront distribution with TTL.

Answer

The files are stored in a different S3 bucket.

Question 8

A developer is troubleshooting a slow-performing Amazon RDS for MySQL database. Which TWO actions should the developer take to improve query performance?

Accepted Answer

Increase the instance size to provide more CPU and memory.. Option A: Enabling slow query log helps identify problematic queries. Option D: Increasing instance size provides more resources. Option B is wrong because Multi-AZ is for availability. Option C is wrong because deleting unused indexes improves write performance, not read. Option E is wrong because deleting logs doesn't improve performance.

Answer

Delete unused indexes to reduce write overhead.

Answer

Enable Multi-AZ deployment for better read performance.

Answer

Delete the binary log files to free up storage.

Question 9

A developer is using AWS CodePipeline to deploy a web application. The pipeline has a source stage from GitHub and a deploy stage to Elastic Beanstalk. The deploy stage fails with the error 'The S3 bucket does not allow access to the artifact'. Which THREE actions could resolve this issue?

Accepted Answer

Add a bucket policy that grants the pipeline's service role access to the artifact bucket.. Option A: The artifact bucket may be in another account; setting bucket policy allows access. Option B: The pipeline role must have permissions to the bucket. Option C: If the artifact bucket is encrypted with KMS, the role needs kms:Decrypt. Option D is wrong because the bucket is already specified. Option E is wrong because versioning is not related to access.

Answer

Specify a different artifact bucket in the pipeline configuration.

Answer

Enable versioning on the artifact bucket.

Question 10

A developer is using AWS X-Ray to trace requests through a microservices application. The developer notices that some traces are incomplete. Which TWO actions can help ensure complete traces?

Accepted Answer

Use the X-Ray SDK to instrument the application code.. Option A: The X-Ray daemon must be running on each EC2 instance to send trace data. Option B: Instrumentation with the SDK sends trace data to the daemon. Option C is wrong because CloudWatch agent is separate. Option D is wrong because the daemon uses UDP. Option E is wrong because the daemon is not centralized.

Answer

Open port 2000 on the security groups for TCP traffic.

Answer

Deploy the X-Ray daemon as a centralized service in a separate instance.

Answer

Install the CloudWatch agent on all instances.

Question 11

Why is the Lambda function not being invoked?

Accepted Answer

The S3 bucket does not have a notification configuration for the Lambda function.. The S3 bucket has no notification configuration to trigger the Lambda function. The Lambda permission allows S3 to invoke, but the bucket must have a NotificationConfiguration event. Option D is correct. Option A is wrong because runtime is supported. Option B is wrong because permission is correct. Option C is wrong because the role is for Lambda execution, not S3 invocation.

Answer

The Lambda execution role does not have permission to be invoked by S3.

Answer

The Lambda permission does not specify the correct source account.

Answer

The Lambda function has a runtime that is not supported.

Question 12

A developer deploys a Lambda function that transforms incoming JSON payloads and writes results to DynamoDB. After a recent code update, the function frequently times out with 5-second durations. The function has a 15-second timeout and 512 MB memory. CloudWatch Logs show no errors. The DynamoDB table has autoscaling enabled. What is the MOST likely cause of the increased duration?

Accepted Answer

A new dependency in the deployment package increased the function's initialization time beyond the duration of the function's reserved concurrency warm start window.. Option A is correct because a new dependency introduced in the update may increase initialization time, leading to timeouts if the function is not provisioned with enough concurrency or if the new library is large. Option B is wrong because Lambda can read from S3 without issue. Option C is wrong because DynamoDB autoscaling handles capacity. Option D is wrong because CloudWatch Logs would show errors if code threw exceptions.

Answer

DynamoDB write capacity is insufficient, causing throttling and retries.

Answer

The function is reading the input payload from S3 instead of API Gateway, causing network latency.

Answer

The function code throws an unhandled exception that is not logged.

Question 13

A developer notices that an EC2 instance running a web application is unreachable via its public IP. The instance passes status checks but security group rules appear correct. What should the developer check NEXT?

Accepted Answer

Check the network ACL associated with the subnet for rules that may block traffic.. The instance passes status checks and security group rules appear correct, which rules out OS-level and security group issues. Since the instance is unreachable via its public IP, the next logical step is to check the network ACL (NACL) associated with the subnet, because NACLs are stateless and can block inbound or outbound traffic even if security groups allow it. NACLs evaluate rules in order by rule number, and a deny rule (or missing allow rule) for the required ephemeral ports (e.g., 1024-65535 for return traffic) could silently drop packets.

Answer

Verify that the instance has an Elastic IP associated.

Answer

Review the route table for a route to an internet gateway.

Answer

Inspect the IAM role attached to the instance for network permissions.

Question 14

A company's application uses Amazon S3 to store user-uploaded images. Users report that recently uploaded images are sometimes not immediately available for viewing. The application uses S3 Event Notifications to trigger a Lambda function that processes images and stores metadata in DynamoDB. What is the MOST likely cause of the delay?

Accepted Answer

S3 Event Notifications may have a slight delay, and the application polls for the processed image before the notification triggers Lambda.. Option B is correct because S3 Event Notifications are typically delivered within seconds but can be delayed; the application should not assume immediate eventual consistency for object reads after writes. Option A is wrong because S3 is eventually consistent for overwrite PUTS of existing keys, but new uploads are strongly consistent. Option C is wrong because Lambda cold start may cause a delay but not minutes. Option D is wrong because DynamoDB is fast.

Answer

Lambda function has a cold start that adds several seconds to processing time.

Answer

S3 is eventually consistent for new object writes, so the object may not be immediately available.

Answer

DynamoDB has insufficient read capacity causing throttling on metadata retrieval.

Question 15

A developer is troubleshooting an AWS Lambda function that processes messages from an Amazon SQS queue. The function is configured with a batch size of 10 and a maximum concurrency of 5. The function frequently reports errors related to message processing timeouts. The function code is idempotent. Which combination of actions will reduce the number of timeouts and improve processing efficiency?

Accepted Answer

Reduce the batch size to 5 and increase the maximum concurrency to 10.. Option D is correct because reducing batch size lowers the work per invocation, and increasing concurrency allows more parallel processing. Option A is wrong because increasing batch size would increase processing time. Option B is wrong because increasing timeout may not solve the root cause if messages are heavy. Option C is wrong because increasing concurrency alone may help but not as much as reducing batch size.

Answer

Increase the function timeout to 30 seconds and set the SQS visibility timeout to 6 minutes.

Answer

Increase the batch size to 20 and increase the function timeout to 30 seconds.

Answer

Increase the maximum concurrency to 10 and set the SQS visibility timeout to 30 seconds.