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

Question 1

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?

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

Accepted Answer

Another resource in the stack failed, triggering a rollback and cancelling the Lambda creation.. The error 'Resource creation cancelled' indicates that the creation of the Lambda function was aborted because another resource in the stack failed. CloudFormation by default rolls back the stack on failure, cancelling any in-progress resource creations. Thus, option C is correct. Option A is incorrect because large code would cause a different error (e.g., 'RequestEntityTooLargeException'). Option B is incorrect because a timeout would show 'CREATE_FAILED' with a timeout message, not 'cancelled'. Option D is incorrect because missing permissions would result in a different error (e.g., 'AccessDeniedException') during invocation, not creation.

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 2

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.. Increasing the instance size provides more CPU and memory, which can improve query processing speed. Option D is correct because enabling the slow query log allows you to identify and analyze poorly performing queries so you can optimize them. Option A is incorrect: while deleting unused indexes reduces write overhead, indexes typically improve read performance, so removing them would not help with slow queries. Option B is incorrect: Multi-AZ deployment is for high availability and failover, not for improving read performance; read replicas would be more appropriate. Option E is incorrect: deleting binary log files frees storage but does not directly improve query 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 3

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.. The X-Ray SDK instruments application code to generate trace segments and sends them to the X-Ray daemon. Option E is correct because the X-Ray daemon must be running on each EC2 instance to receive trace data from the SDK and forward it to the X-Ray service. Without both, traces may be incomplete. Option B is incorrect because the X-Ray daemon communicates over UDP, not TCP, and port 2000 is UDP; opening TCP 2000 does not help. Option C is incorrect because the X-Ray daemon is designed to run locally on each instance, not as a centralized service. Option D is incorrect because the CloudWatch agent does not handle X-Ray traces; it is used for CloudWatch metrics and logs.

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 4

A developer runs a script that uses the AWS CLI to copy a large number of files from an on-premises server to an S3 bucket. The copy operation fails partway through with a 'RequestTimeout' error. What is the MOST efficient way to resume the copy and ensure all files are transferred?

Accepted Answer

Use the aws s3 sync command to synchronize the source directory with the S3 bucket.. The `aws s3 sync` command is the most efficient way to resume the copy because it automatically compares the source directory with the destination S3 bucket and transfers only the files that are missing or have been modified. This avoids re-uploading already transferred files, directly addressing the partial failure without manual intervention or unnecessary overhead.

Answer

Delete the S3 bucket and restart the copy operation.

Answer

Use the cp command with the --recursive flag to copy the remaining files.

Answer

Increase the --cli-read-timeout value in the AWS CLI configuration and retry the original command.

Question 5

A developer is troubleshooting a slow-running query on an Amazon RDS for MySQL database. The query is used by a reporting application and takes over 30 seconds to complete. The database is a db.r5.large instance with 200 GB of gp2 storage. Which TWO actions should the developer take to improve query performance?

Accepted Answer

Review the slow query log to identify the query and its execution plan.. Reviewing the slow query log helps identify the query and its execution plan, which is essential for diagnosing performance issues. Option D is correct: adding appropriate indexes can speed up query execution by reducing the number of rows scanned. Option A is incorrect: terminating idle connections frees up resources but does not directly improve query performance for a slow-running query. Option C is incorrect: increasing storage to gp2 does not improve I/O performance; gp2 performance scales with size only up to a point, but the primary bottleneck is likely query optimization, not storage. Option E is incorrect: Multi-AZ is for high availability and failover, not for enhancing read performance.

Answer

Terminate idle connections to free up resources.

Answer

Increase the allocated storage to 500 GB to improve I/O performance.

Answer

Enable Multi-AZ deployment for better read performance.

Question 6

A company is running a serverless application using AWS Lambda and Amazon API Gateway. The application experiences increased latency during peak hours. CloudWatch metrics show that Lambda function duration remains stable, but API Gateway latency spikes. Which THREE actions should the developer take to reduce API Gateway latency?

Accepted Answer

Enable compression for API responses.. Options B, D, and E are correct. Enabling compression reduces payload size, decreasing response time. API Gateway caching reduces backend calls by serving cached responses, lowering latency. Switching to Regional endpoint reduces network latency by eliminating the global edge network hop. Option A is wrong because increasing Lambda timeout does not reduce API Gateway latency; it only allows functions to run longer. Option C is wrong because throttling limits cap request rates but do not reduce latency for individual requests.

Answer

Increase the Lambda function timeout.

Answer

Increase the API Gateway throttling limits.

Question 7

A developer is deploying a new microservice on AWS Elastic Beanstalk. The service uses an RDS database. The developer wants to ensure that database credentials are not stored in the application's source code. Which TWO methods should the developer use to securely provide credentials to the application?

Accepted Answer

Use AWS Secrets Manager to store and retrieve the credentials at runtime.. Options A and C are correct. AWS Secrets Manager allows you to store and automatically rotate database credentials, and retrieve them securely at runtime via API calls, avoiding hardcoding. Elastic Beanstalk environment properties let you set environment variables that the application can read, and these properties can be configured to reference secrets from Secrets Manager (e.g., using the `aws-secrets-manager` namespace). Option B is incorrect because storing credentials in source code exposes them in version control and is insecure. Option D is incorrect because storing credentials in an encrypted file on an EC2 instance still requires managing the encryption key and is not a recommended practice for Elastic Beanstalk. Option E is incorrect because an S3 bucket with a public read policy makes the credentials publicly accessible, violating security best practices.

Answer

Store the credentials in a configuration file within the application source code.

Answer

Store the credentials in an encrypted file on an EC2 instance.

Answer

Store the credentials in an S3 bucket with a public read policy.

Question 8

A company runs a critical application on Amazon EC2 instances behind an Application Load Balancer (ALB). The application experiences intermittent errors where some requests return HTTP 503 (Service Unavailable) errors. The developers have verified that the application code is healthy and the EC2 instances pass health checks. The ALB health check is configured to hit a specific endpoint (/health) with a healthy threshold of 2 and an unhealthy threshold of 2. The health check interval is 30 seconds, and the timeout is 5 seconds. The application's /health endpoint sometimes takes up to 6 seconds to respond due to a dependency on a third-party service. The developers want to minimize the 503 errors without changing the application code. Which action should the developer take?

Accepted Answer

Increase the health check timeout to 10 seconds to accommodate the slow /health endpoint.. The correct action is to increase the health check timeout from 5 seconds to 10 seconds. Since the /health endpoint sometimes takes up to 6 seconds to respond, the current timeout of 5 seconds causes the ALB to consider the instance unhealthy, leading to 503 errors. By increasing the timeout, the ALB will wait longer for a response, reducing unnecessary health check failures. Option B is wrong because decreasing the unhealthy threshold would make instances even more sensitive, increasing 503 errors. Option C is wrong because deregistration delay affects connection draining during instance termination, not health check behavior. Option D is wrong because decreasing the health check interval does not help; the issue is timeout, not frequency.

Answer

Decrease the unhealthy threshold to 1 so that instances are marked unhealthy after one failed health check.

Answer

Increase the deregistration delay to 300 seconds to allow connections to drain.

Answer

Decrease the health check interval to 10 seconds to detect health changes faster.

Question 9

A company runs a web application on EC2 instances behind an Application Load Balancer (ALB). Users report intermittent 503 errors. The ALB health checks are failing for a few instances, but the instances themselves are running and have healthy application processes. What is the MOST likely cause?

Accepted Answer

The security group for the EC2 instances is not allowing traffic from the ALB.. The ALB health checks are failing despite the instances and application processes being healthy, which indicates a network-level issue. The most likely cause is that the EC2 instances' security group is not allowing inbound traffic from the ALB's security group on the health check port (e.g., HTTP/HTTPS). Without this rule, the ALB cannot reach the health check endpoint, marking the instances as unhealthy and causing intermittent 503 errors when traffic is routed to those instances.

Answer

The ALB is not scaled to handle the traffic.

Answer

The DNS resolution via Route53 is misconfigured.

Answer

Sticky sessions are not enabled on the ALB.

Question 10

A developer is optimizing a Node.js Lambda function that processes CSV files from S3. The function reads the entire file into memory, processes it, and writes results to DynamoDB. For large files, the function runs out of memory. What is the MOST effective optimization?

Accepted Answer

Use the AWS SDK's S3 GetObject with a stream and process in chunks.. Using the AWS SDK's S3 GetObject with a stream allows the function to process the CSV file in chunks, avoiding loading the entire file into memory. This directly addresses the memory issue for large files. Option A is incorrect because increasing timeout does not reduce memory usage. Option B is incorrect because while increasing memory might help, it does not solve the root cause and may increase costs; streaming is more efficient. Option D is incorrect because S3 Select is used to filter columns from S3 objects using SQL, but it does not solve the problem of loading the entire file into memory; it could reduce the data transferred but the function still needs to handle streaming or chunking.

Answer

Increase the Lambda timeout to allow more processing time.

Answer

Increase the Lambda function memory to 3008 MB.

Answer

Use S3 Select to retrieve only necessary columns.

Question 11

A developer notices that an S3 bucket policy allows public read access to all objects. The bucket contains sensitive data that should only be accessible by authorized IAM users. What is the BEST way to remediate this?

Accepted Answer

Modify the bucket policy to remove the public statement and use IAM policies for access.. The bucket policy currently grants public read access, which overrides any IAM-based restrictions. By removing the public statement from the bucket policy and relying solely on IAM policies, access is controlled at the user level, ensuring only authorized IAM users can read objects. This aligns with the principle of least privilege and follows AWS best practices for securing S3 data.

Answer

Enable default encryption on the bucket.

Answer

Enable S3 Block Public Access at the account level.

Answer

Enable S3 Object Ownership and use ACLs.

Question 12

A developer is troubleshooting a slow-running Amazon RDS for PostgreSQL instance. Which TWO metrics should the developer examine in Amazon CloudWatch to identify a possible resource bottleneck?

Accepted Answer

CPUUtilization. High CPU utilization indicates a CPU bottleneck, which can slow down query processing. Option B is correct because high ReadIOPS and WriteIOPS accompanied by a high Average Queue Depth signal an I/O bottleneck, where the storage subsystem cannot keep up with requests. Option C is incorrect because FreeableMemory alone does not directly indicate a performance bottleneck; while low memory can cause issues, it is not a primary metric for resource bottlenecks. Option D is incorrect because NetworkThroughput is rarely a limiting factor for RDS performance; the database typically processes requests faster than network bandwidth constraints. Option E is incorrect because DatabaseConnections only indicates the number of connections, not a direct resource bottleneck; performance problems are better captured by CPU or I/O metrics.

Answer

FreeableMemory

Answer

NetworkThroughput

Answer

DatabaseConnections

Question 13

A company is using Amazon S3 to store log files. The logs are rarely accessed after 30 days but must be retained for 7 years for compliance. Which THREE actions should the company take to optimize storage costs?

Accepted Answer

Use S3 Lifecycle policy to transition objects to S3 Glacier after 1 year.. Transitioning objects to S3 Glacier after 1 year reduces storage costs for long-term retention while maintaining compliance. Option D is correct because lifecycle policies can expire objects after 7 years, meeting the retention requirement. Option E is correct because transitioning to S3 Standard-IA after 30 days optimizes costs for infrequently accessed logs. Option A is wrong because deleting objects after 30 days violates the 7-year retention requirement. Option B is wrong because S3 One Zone-IA lacks the durability needed for compliance data and is not cost-effective if logs are accessed frequently in the first 30 days.

Answer

Use S3 Lifecycle policy to delete objects after 30 days.

Answer

Store objects in S3 One Zone-IA from the start.

Question 14

A developer receives an AccessDenied error when trying to put an object into an S3 bucket using the AWS SDK. The IAM user has an attached policy that grants s3:PutObject on the bucket. What is the MOST likely cause of the error?

Accepted Answer

The bucket policy explicitly denies the action.. The most likely cause is that the bucket policy explicitly denies the s3:PutObject action. IAM policies grant permissions, but S3 bucket policies can override them with an explicit deny, which takes precedence over any allow. Since the IAM user already has an attached policy allowing s3:PutObject, the only way to get an AccessDenied error is if a bucket policy explicitly denies the action.

Answer

The request is being throttled by S3.

Answer

The object key is too long.

Answer

The AWS SDK version is outdated.

Question 15

An application running on Amazon EC2 instances behind an Application Load Balancer (ALB) is experiencing intermittent 503 errors. The EC2 instances are in an Auto Scaling group. What is the MOST likely cause?

Accepted Answer

The target group health checks are failing.. The intermittent 503 errors indicate that the ALB temporarily has no healthy targets to forward requests to. When target group health checks fail, the ALB marks instances as unhealthy and stops routing traffic to them, causing a 503 response if all instances are unhealthy. This aligns with the Auto Scaling group potentially launching new instances that haven't passed health checks yet, or existing instances failing health checks due to application overload or misconfiguration.

Answer

The SSL certificate on the ALB has expired.

Answer

The ALB DNS name is not resolving.

Answer

The security group for the ALB is blocking traffic.