DVA-C02 Troubleshooting and Optimization Practice Test 11 — 15 Questions

Question 1

A developer invokes a Lambda function from the AWS CLI and receives the response shown in the exhibit. The output file contains an error message. What is the MOST likely cause of the FunctionError field being set to 'Unhandled'?

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

Accepted Answer

The function code threw an uncaught exception.. The 'FunctionError' field set to 'Unhandled' indicates that the Lambda function failed with an error that was not caught by the function's code, such as an uncaught exception. This is the most likely cause. Option A is incorrect because permission errors to CloudWatch Logs would result in a 403 error, not an 'Unhandled' error. Option B is incorrect because the payload size limit for synchronous invocation is 6 MB, not 6 KB; exceeding limits would cause a 413 error, not 'Unhandled'. Option D is incorrect because a timeout would return a 200 status code with 'FunctionError' set to 'Unhandled', but the most common 'Unhandled' error is an uncaught exception, making option C the most likely cause.

Answer

The function's execution role does not have permission to write to CloudWatch Logs.

Answer

The invocation request payload exceeded the 6 KB limit for synchronous invocation.

Answer

The function timed out before completing execution.

Question 2

A developer uses the CloudFormation template in the exhibit to create an S3 bucket. The stack creation fails with the error 'Bucket already exists'. What is the MOST likely reason?

Accepted Answer

The bucket name is already taken by another AWS account.. S3 bucket names must be globally unique. If the bucket name 'my-unique-bucket-name' already exists in another AWS account, the creation will fail. Option A is incorrect because invalid JSON syntax would cause a different error, not 'Bucket already exists'. Option C (permissions) would result in an authorization error. Option D is incorrect because bucket name availability is global, not region-specific; if the name exists globally, it fails regardless of region.

Answer

The CloudFormation template has invalid JSON syntax.

Answer

The IAM user does not have permission to create S3 buckets.

Answer

The bucket name is not available in the specified region.

Question 3

A developer is troubleshooting a Lambda function that intermittently times out. The function makes HTTP requests to an external API. The function's CloudWatch logs show 'Task timed out after 3.01 seconds'. What is the MOST likely cause?

Accepted Answer

The Lambda function timeout is set to 3 seconds, but the HTTP request takes longer.. The Lambda function timeout is set to 3 seconds, and the HTTP request to the external API takes longer than that, causing the 'Task timed out after 3.01 seconds' error. Option B is incorrect because throttling due to insufficient reserved concurrency would result in a 'Rate exceeded' error, not a timeout. Option C is incorrect because if the function couldn't reach the external API due to VPC configuration, it would result in a connection error, not a timeout. Option D is incorrect because a missing IAM role would prevent the function from executing at all, and the logs show the function started execution.

Answer

The Lambda function has insufficient reserved concurrency causing throttling.

Answer

The Lambda function is not configured with a VPC and cannot reach the external API.

Answer

The Lambda function is not starting execution due to a missing IAM role.

Question 4

A company runs a production web application on EC2 instances behind an Application Load Balancer. Users report intermittent 502 errors. The developers find that the ALB access logs show 'target_response_code' of 502 for some requests. What is the MOST likely cause?

Accepted Answer

The EC2 instances are closing idle connections prematurely due to a short keep-alive timeout.. The 502 Bad Gateway error from an Application Load Balancer indicates that the target (EC2 instance) closed the connection before the ALB could finish writing the request or reading the response. This commonly occurs when the keep-alive timeout on the EC2 instance is set too low, causing idle connections to be closed prematurely. Option A is incorrect because DNS resolution issues would not cause a 502; they would cause a 503 or connection failure. Option B is incorrect because a security group blocking traffic would result in health check failures and a 503, not a 502. Option D is incorrect because unhealthy instances would cause a 503, not a 502.

Answer

The EC2 instances are unable to resolve DNS for the ALB.

Answer

The security group for the EC2 instances is blocking traffic from the ALB.

Answer

The ALB health checks are failing and the target group has unhealthy instances.

Question 5

A developer is optimizing an S3 bucket that stores large CSV files for analytics. The files are accessed frequently for the first 30 days, then rarely accessed. After 90 days, the data must be retained for compliance but accessed infrequently. What is the MOST cost-effective lifecycle policy?

Accepted Answer

Transition to S3 Standard-IA after 30 days, then to S3 Glacier Deep Archive after 90 days.. It transitions to S3 Standard-IA after 30 days (when access becomes infrequent) and then to S3 Glacier Deep Archive after 90 days (for long-term compliance at lowest cost). This matches the access pattern: frequent for first 30 days, then rarely accessed, then after 90 days infrequent access for compliance.

Option A (Intelligent-Tiering) is not the most cost-effective because it incurs monitoring costs and is designed for unknown or changing access patterns, but here the pattern is known.

Option B (One Zone-IA then delete) is not suitable because it deletes after 90 days, but data must be retained for compliance. Also One Zone-IA has lower durability.

Option D (Glacier Flexible Retrieval after 30 days then Deep Archive after 90 days) is not cost-effective because transitioning to Glacier Flexible Retrieval after 30 days would incur higher retrieval costs and longer access times for the first 90 days, and it's better to use Standard-IA for that period.

Answer

Use S3 Intelligent-Tiering to automatically move data between access tiers.

Answer

Transition to S3 One Zone-IA after 30 days, then delete after 90 days.

Answer

Transition to S3 Glacier Flexible Retrieval after 30 days, then to S3 Glacier Deep Archive after 90 days.

Question 6

A company has a DynamoDB table with a global secondary index (GSI) for querying. The write capacity is provisioned at 1000 WCU, and the GSI has 500 WCU. During a traffic spike, writes to the table are throttled, but the GSI is not throttled. What is the MOST likely cause?

Accepted Answer

The total write traffic to the table exceeds 1000 WCU.. The table is throttling due to write traffic exceeding its provisioned write capacity of 1000 WCU. The global secondary index (GSI) has its own write capacity of 500 WCU, and if the writes to the GSI are within that limit, the GSI will not be throttled. Option A is incorrect because DynamoDB adaptive capacity automatically adjusts throughput to handle traffic spikes, but it does not reduce the table's provisioned capacity; it helps prevent throttling. Option B is incorrect because a hot partition would cause throttling on specific partitions, which would likely also affect the GSI since it uses the same partition key; moreover, the scenario indicates general throttling, not just on a partition. Option D is incorrect because the GSI is not throttled, so its write capacity is not the issue.

Answer

DynamoDB adaptive capacity is reducing the table's write capacity.

Answer

A hot partition in the table is exceeding its partition-level write limits.

Answer

The GSI is throttling writes because its write capacity is insufficient.

Question 7

A company is using AWS Elastic Beanstalk for a Node.js application. The environment's health is 'Severe' and the logs show 'ELB health check target http://:80/ is not responding'. What is the MOST likely cause?

Accepted Answer

The application is listening on a different port than the health check expects.. The health check target 'http://:80/' indicates that the load balancer is trying to connect to port 80 on the EC2 instances, but the application is not listening on that port (for example, if a Node.js developer hardcoded port 3000 instead of using the environment's PORT variable). Option A is incorrect because if the application were not deployed, the error would typically be a 503 or 'no healthy instances' rather than a specific health check target not responding. Option C is incorrect because Elastic Beanstalk automatically configures and manages the security groups to allow traffic between the load balancer and the EC2 instances, making an application port misconfiguration much more likely. Option D is incorrect because the load balancer is configured to listen on port 80, as shown by the health check target, so the issue is on the instance side.

Answer

The application is not deployed to the EC2 instances.

Answer

The security group for the EC2 instances is blocking traffic on port 80.

Answer

The load balancer is not configured to listen on port 80.

Question 8

A developer is optimizing an API Gateway REST API that uses Lambda integration. The response times are high, and CloudWatch logs show that the Lambda function has cold starts frequently. The function is written in Java and uses a large library. What is the MOST effective optimization?

Accepted Answer

Enable provisioned concurrency on the Lambda function.. Provisioned concurrency initializes the function and keeps it warm, eliminating cold starts entirely. This is the most effective optimization for a Java Lambda function with a large library. Option A (rewriting in Node.js) reduces cold start time but requires significant code changes and does not address the root cause as directly. Option B (increasing memory) may reduce cold start time slightly but is not as effective. Option D (AWS SDK for Java 2.x) improves initialization time but does not prevent cold starts.

Answer

Rewrite the function in Node.js to reduce cold start time.

Answer

Increase the Lambda function's memory allocation to 3008 MB.

Answer

Use the AWS SDK for Java 2.x to reduce initialization time.

Question 9

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.. Creating a read replica allows read queries to be directed to the replica, offloading the read workload from the primary instance and reducing its CPU utilization. Option A is incorrect because upgrading to a larger instance class increases capacity but does not specifically address read-heavy workloads efficiently and is less cost-effective than scaling reads with replicas. Option C is incorrect because Multi-AZ provides high availability and automatic failover, not performance improvement or load reduction. Option D is incorrect because purchasing reserved instances reduces costs but does not affect CPU utilization.

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 10

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.. Configuring the SQS queue's redrive policy with a maxReceiveCount of 2 ensures that the message will be retried up to 2 times before being moved to a dead-letter queue (DLQ). This guarantees at least one retry if the first processing fails. Option A is incorrect because a DLQ alone does not trigger retries; it only stores messages that have failed after maxReceiveCount attempts. Option C is incorrect because setting retry attempts to 0 would prevent any retries at all. Option D is incorrect because increasing the visibility timeout does not cause retries; it only extends the time the message is hidden from other consumers.

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 11

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. To identify if an Amazon RDS database is the bottleneck of a slow web application, a developer should examine CPUUtilization and DatabaseConnections. High CPUUtilization on the RDS instance indicates that the database is busy processing complex queries, performing full table scans, or handling high load. DatabaseConnections shows the number of active client connections; if this is high, it can exhaust the database's connection pool and lead to queueing or connection timeouts. Other metrics like RequestCount (ALB) and NetworkIn are not direct indicators of a database bottleneck.

Answer

RequestCount

Answer

NetworkIn

Answer

ReadIOPS and WriteIOPS

Question 12

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 A and C are correct. Verifying the target group's health check path and port (A) ensures that the load balancer's health check matches the application's actual endpoint, which is a common cause of health check failures. Checking the CodeDeploy deployment logs (C) provides detailed error messages from the deployment process, which can pinpoint why the health checks are failing. Option B (checking S3 bucket) is not directly related to health check failures, as artifacts are typically stored correctly if the build succeeded. Option D (checking CodeBuild logs) is irrelevant because the build stage succeeded. Option E (increasing instances) does not address the root cause of health check failures.

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 13

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 E are correct. Purchasing Reserved Instances (A) provides significant discounts for steady-state production workloads. Using Spot Instances (B) is cost-effective for fault-tolerant workloads that can handle interruptions. AWS Instance Scheduler (E) automatically stops development instances during non-business hours, reducing costs. Option C is incorrect because gp3 volumes are generally more expensive than gp2 for the same performance; the cost savings from gp3 come from optimized performance, but it is not a guaranteed cost reduction. Option D is incorrect because increasing instance size typically increases costs, not reduces them.

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 14

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 's3:GetObject' permission to read the object from S3. When the function is triggered by an actual S3 event, it uses this role. The console test may use a different role or bypass permissions, masking the issue. Option B correctly identifies that the execution role lacks the required permission. Option A is incorrect because versioning does not cause 'AccessDenied' for reads. Option C is incorrect because the bucket policy granting access to the Lambda service principal is not required; the execution role handles permissions. Option D is incorrect because Lambda and S3 do not need to be in the same VPC.

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 15

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 that visualizes database load and identifies the top SQL queries causing high CPU utilization. It is the correct service for analyzing database query performance. AWS CloudWatch Logs Insights is for analyzing log data, not database queries. AWS X-Ray traces application requests but does not analyze database queries. RDS Enhanced Monitoring provides OS-level metrics but lacks query-level detail.

Answer

RDS Enhanced Monitoring

Answer

AWS X-Ray

Answer

CloudWatch Logs Insights