DVA-C02 Troubleshooting and Optimization Practice Test 18 — 15 Questions

Question 1

A developer is troubleshooting an Amazon RDS for MySQL instance that is experiencing high CPU utilization. The application performs many read operations. The developer wants to reduce the load on the database. What is the MOST effective solution?

Accepted Answer

Create a read replica and direct read queries to it.. Option C is correct because adding a read replica offloads read traffic from the primary instance, reducing CPU utilization. Option A is wrong because vertical scaling increases capacity but does not specifically address read load efficiently. Option B is wrong because reserved instances do not reduce CPU usage. Option D is wrong because Multi-AZ provides high availability, not performance improvement.

Answer

Upgrade the DB instance to a larger instance class.

Answer

Enable Multi-AZ for automatic failover.

Answer

Purchase reserved instances to reduce costs.

Question 2

A company has a Lambda function that processes messages from an SQS queue. The function sometimes fails to process a message, and the message is not retried. The developer wants to ensure that failed messages are retried at least once. What should the developer do?

Accepted Answer

Configure the SQS queue's redrive policy with a maxReceiveCount of 2 and a DLQ.. Option D is correct because setting the SQS redrive policy with a DLQ and configuring the Lambda function with a maximum retry count of 2 ensures retries. Option A is wrong because increasing the visibility timeout without a DLQ does not guarantee retries. Option B is wrong because DLQ alone does not enable retries. Option C is wrong because Lambda's default retry behavior is not sufficient without proper DLQ configuration.

Answer

Configure a dead-letter queue (DLQ) for the SQS queue.

Answer

Set the Lambda function's retry attempts to 0 in the event source mapping.

Answer

Increase the SQS queue's visibility timeout to 6 hours.

Question 3

A developer is troubleshooting a slow web application. The application uses an Application Load Balancer, EC2 instances, and an RDS database. The developer suspects the database is the bottleneck. Which TWO CloudWatch metrics should the developer examine to confirm this? (Select TWO.)

Accepted Answer

DatabaseConnections. Options B and D are correct. DatabaseConnections shows current connections; ReadIOPS and WriteIOPS show disk I/O, which can cause slowness. Option A (CPUUtilization) is a general metric, but for database bottleneck, I/O and connections are more indicative. Option C (NetworkIn) is more about network load. Option E (RequestCount) is for the ALB, not the database.

Answer

RequestCount

Answer

NetworkIn

Answer

CPUUtilization

Question 4

A company is using AWS CodePipeline for CI/CD. The pipeline has a build stage using AWS CodeBuild, and a deploy stage using AWS CodeDeploy. The deployment is failing with 'Error: Health checks failed'. Which TWO steps should the developer take to troubleshoot this issue? (Select TWO.)

Accepted Answer

Verify that the target group's health check path and port are correctly configured.. Options B and D are correct. Checking the CodeDeploy deployment logs (B) will show detailed error messages. Verifying the target group's health check configuration (D) ensures the application is responding correctly. Option A (checking CodeBuild logs) is irrelevant because the build stage succeeded. Option C (increasing instance count) does not address health check failure. Option E (checking S3 bucket) is not directly related.

Answer

Check the S3 bucket where the build artifacts are stored.

Answer

Check the CodeBuild build logs for errors.

Answer

Increase the number of EC2 instances in the Auto Scaling group.

Question 5

A developer is optimizing costs for an AWS account. The account has multiple EC2 instances running different workloads. Some instances are used for development and are only needed during business hours. Which THREE actions can the developer take to reduce costs? (Select THREE.)

Accepted Answer

Purchase Reserved Instances for the production instances.. Options A, B, and D are correct. Using Spot Instances (A) reduces costs for fault-tolerant workloads. Scheduling instances to stop during off-hours (B) saves money. Reserving instances (D) provides discounts for steady-state workloads. Option C (increasing instance size) increases costs. Option E (using EBS gp3) may reduce storage costs but is not specific to the described scenario.

Answer

Use EBS gp3 volumes instead of gp2 to save on storage costs.

Answer

Increase the instance size to handle peak load more efficiently.

Question 6

A developer is troubleshooting a Lambda function that processes S3 events. The function runs successfully in the AWS Management Console test but fails when triggered by actual S3 PUT events. The error logs show 'AccessDenied' when attempting to read the object from S3. What is the most likely cause?

Accepted Answer

The Lambda execution role lacks 's3:GetObject' permission for the bucket.. The Lambda function's execution role must have permission to read the S3 object. The error occurs only with actual events because the console test may use a different role or the event payload differs. Option C directly addresses the missing permission. Option A is wrong because S3 events do not require VPC access. Option B is wrong because the bucket policy may not grant access to the Lambda service principal. Option D is wrong because S3 event notifications do not have versioning restrictions.

Answer

The S3 bucket has versioning enabled and the event does not include the version ID.

Answer

The S3 bucket policy does not grant 's3:GetObject' to the Lambda service principal.

Answer

The Lambda function is not in the same VPC as the S3 bucket.

Question 7

A developer notices that an RDS MySQL instance's CPU utilization is consistently above 80% during peak hours. Which AWS service can be used to analyze the database queries and identify the root cause?

Accepted Answer

RDS Performance Insights. RDS Performance Insights provides a dashboard to analyze database load and identify top SQL queries. Option B is the correct service. CloudWatch Logs Insights (A) is for log analysis, not database query performance. AWS X-Ray (C) traces requests, not database queries. RDS Enhanced Monitoring (D) provides OS-level metrics but not query-level detail.

Answer

RDS Enhanced Monitoring

Answer

AWS X-Ray

Answer

CloudWatch Logs Insights

Question 8

A company's DynamoDB table has a read capacity of 10,000 RCUs and receives consistent traffic. Recently, users have reported increased latency for read requests. The application uses strongly consistent reads. The developer checks CloudWatch metrics and sees that 'ConsumedReadCapacityUnits' is at 9,500 but 'ThrottledRequests' is high. What is the most likely cause?

Accepted Answer

A hot partition is exceeding its partition-level read capacity.. Strongly consistent reads consume twice the RCUs of eventually consistent reads. If the application requests strongly consistent reads, the actual consumed capacity is double the read request units, so 9,500 RCUs consumed may represent only 4,750 read requests, but the provisioned capacity is 10,000. However, throttling occurs because the partition-level capacity may be exceeded. Option C is correct: a hot partition causes throttling even if table-level capacity is not exhausted. Option A is incorrect because the table has capacity. Option B is incorrect because RCUs are sufficient. Option D is incorrect as strongly consistent reads are working.

Answer

The application is using eventually consistent reads but expecting strongly consistent results.

Answer

The DynamoDB table has auto scaling enabled and is scaling down too aggressively.

Answer

The provisioned read capacity is too low for the traffic.

Question 9

A developer is deploying a new version of a Lambda function using AWS CodeDeploy. The deployment fails with a 'DeploymentLimitExceeded' error. What is the most likely cause?

Accepted Answer

The deployment group has reached the maximum number of concurrent deployments.. AWS CodeDeploy has a limit on the number of concurrent deployments per deployment group. Option D is correct. The error indicates the limit is exceeded. Option A is incorrect because deployment limits are per deployment group, not per function. Option B is incorrect because the error is not about version conflicts. Option C is incorrect because the error is not about IAM permissions.

Answer

The Lambda function has reached the maximum number of versions.

Answer

Another deployment is in progress for the same Lambda function.

Answer

The IAM role for CodeDeploy does not have sufficient permissions.

Question 10

A developer is troubleshooting an EC2 instance that is unreachable via SSH. The instance passed the status checks, and the security group allows SSH from the developer's IP. What should the developer check next?

Accepted Answer

The network ACL's outbound rules.. The network ACL is stateless and must allow both inbound and outbound traffic. Option B is correct: the outbound ephemeral port range must be allowed for the return traffic. Option A is wrong because the security group is stateful and allows return traffic automatically. Option C is wrong because the instance is reachable for status checks. Option D is wrong because route tables do not affect direct connectivity to the instance from the internet if it has a public IP.

Answer

The security group's outbound rules.

Answer

The route table for the subnet.

Answer

The instance's system log for kernel errors.

Question 11

A developer is trying to decrypt an S3 object using an AWS KMS key. The decryption fails with an 'AccessDenied' error. The IAM policy attached to the developer's user includes the statement in the exhibit. The KMS key policy includes the following statement:

{
  "Sid": "Enable IAM User Permissions",
  "Effect": "Allow",
  "Principal": {
    "AWS": "arn:aws:iam::123456789012:root"
  },
  "Action": "kms:*",
  "Resource": "*"
}

What is the most likely reason for the failure?

Accepted Answer

The developer's IAM policy does not include 'kms:GenerateDataKey' permission.. The IAM policy only grants kms:Decrypt, but to decrypt an S3 object, the developer also needs kms:GenerateDataKey (if using envelope encryption) or kms:ReEncrypt. However, the most common issue is that the IAM policy does not allow the necessary action. Option B is correct because the developer's IAM policy lacks 'kms:GenerateDataKey' which is often needed. Option A is wrong because the key policy allows IAM users. Option C is wrong because the key policy uses the root account. Option D is wrong because the key policy does not restrict the principal.

Answer

The KMS key policy does not grant access to the developer's IAM user.

Answer

The KMS key policy specifies 'kms:*' which is too broad and causes a conflict.

Answer

The developer's IAM policy uses 'Resource' with the full key ARN but the key policy requires a different format.

Question 12

A developer is using AWS CloudFormation to deploy a stack. The stack creation fails with a 'CREATE_FAILED' status for an EC2 instance resource. The event message says 'The requested configuration is currently not supported. Please check the documentation for supported configurations.' What should the developer do to resolve this issue?

Accepted Answer

Change the instance type or specify a different Availability Zone in the template.. The error indicates the instance type is not available in the specified Availability Zone. Option A is correct: changing the instance type or AZ resolves it. Option B is wrong because the error is not about permissions. Option C is wrong because the stack creation failed; updating the stack is not possible. Option D is wrong because the error is not about the AMI.

Answer

Update the stack with a new parameter value.

Answer

Add an IAM role to the EC2 instance.

Answer

Use a different Amazon Machine Image (AMI).

Question 13

A company's API Gateway REST API is experiencing high latency. The API integrates with a Lambda function that queries an RDS database. The developer notices that the Lambda function's duration metric is low, but the API Gateway integration latency is high. What is the most likely cause?

Accepted Answer

The Lambda function is in a VPC, causing additional network hops.. API Gateway integration latency includes network overhead and other factors. Option C is correct: if the Lambda function is in a VPC, the network traversal between API Gateway and the VPC can cause latency. Option A is wrong because the Lambda duration is low. Option B is wrong because caching would reduce latency, not increase it. Option D is wrong because the database is not queried directly by API Gateway.

Answer

The Lambda function has reached the concurrency limit.

Answer

The API Gateway cache is enabled and causing a cache miss for every request.

Answer

The RDS database is in a different region than the API Gateway.

Question 14

A developer is using SQS to decouple microservices. The producer sends messages, but the consumer (an EC2 instance) does not process them. The CloudWatch metric 'ApproximateNumberOfMessagesVisible' is increasing. The consumer's IAM role has 'sqs:ReceiveMessage' and 'sqs:DeleteMessage' permissions. What is the most likely cause?

Accepted Answer

The consumer is not using long polling, so calls to ReceiveMessage return empty frequently.. The consumer must also have 'sqs:ChangeMessageVisibility' to extend the visibility timeout if needed, but the key issue is that the consumer may not be calling ReceiveMessage with the correct queue URL or there is a network issue. However, the most common cause is that the visibility timeout is too short and messages are not being deleted before becoming visible again, but that would cause the metric to fluctuate. Another possibility is that the consumer is polling the wrong queue. Option D is correct: the consumer is not using long polling, which can lead to empty responses and the impression that there are no messages. Option A is wrong because the permissions include ReceiveMessage. Option B is wrong because a DLQ would receive messages after max receives, but messages are still visible. Option C is wrong because the queue is not encrypted by default.

Answer

A dead-letter queue is configured and messages are being moved there.

Answer

The consumer does not have permission to call 'sqs:ReceiveMessage'.

Answer

The queue is encrypted with SSE, and the consumer does not have permission to use the KMS key.

Question 15

A developer is troubleshooting a slow-running application that uses ElastiCache for Redis as a caching layer. The application frequently reads and writes data to the cache. Which TWO actions should the developer take to improve cache performance?

Accepted Answer

Use optimized data structures like hashes instead of strings for complex data.. Option A is correct: enabling auto scaling for ElastiCache can adjust capacity based on demand. Option D is correct: optimizing data structures reduces memory and CPU overhead. Option B is wrong: TTL eviction is already handled by Redis. Option C is wrong: more nodes increase complexity and may not help if the bottleneck is CPU. Option E is wrong: disabling persistence improves write performance but may not be the primary issue.

Answer

Configure the cache to use LRU eviction policy.

Answer

Disable persistence by setting appendonly to no.

Answer

Increase the number of shards to distribute data.