DVA-C02 Troubleshooting and Optimization Practice Test 5 — 15 Questions

Question 1

A company runs a monolithic application on EC2 Behind an Application Load Balancer. They want to migrate to a microservices architecture using ECS Fargate. What is the most important optimization to ensure minimal downtime during the migration?

Accepted Answer

Use a blue/green deployment strategy with weighted target groups.. Option A is correct because a blue/green deployment strategy with weighted target groups allows you to gradually shift traffic from the existing monolithic EC2 application (blue) to the new microservices on ECS Fargate (green) while monitoring for errors. This minimizes downtime by enabling instant rollback if issues arise, and it leverages Application Load Balancer (ALB) features like stickiness and health checks to ensure a seamless transition without disrupting active connections.

Answer

Increase the EC2 instance size to handle the microservices load.

Answer

Deploy all microservices in a single ECS service for simplicity.

Answer

Scale horizontally by adding more EC2 instances.

Question 2

A developer notices that an S3 bucket used for static website hosting returns 403 Forbidden for anonymous requests. The bucket policy allows s3:GetObject for Principal "*". What is the most likely issue?

Accepted Answer

The S3 Block Public Access settings are enabled.. D is correct because S3 Block Public Access settings, when enabled at the account or bucket level, override any bucket policy or ACL that grants public access. Even though the bucket policy allows s3:GetObject for Principal "*", the Block Public Access settings explicitly deny all public requests, resulting in a 403 Forbidden error for anonymous users.

Answer

The bucket does not have server access logging enabled.

Answer

The bucket ACL does not allow public read.

Answer

The bucket policy is not attached to the correct bucket.

Question 3

A developer is optimizing a DynamoDB table for a gaming leaderboard. The table stores player scores and is read-heavy. Queries often fetch the top 10 scores. Which indexing strategy best reduces RCU consumption?

Accepted Answer

Create a global secondary index with score as the sort key.. A global secondary index (GSI) with score as the sort key allows efficient retrieval of the top 10 scores by querying the index in descending order, reading only the required items. This minimizes read capacity unit (RCU) consumption compared to scanning the base table, as each query reads exactly 10 items (or fewer) rather than consuming RCUs for a full table scan or filtering large result sets.

Answer

Create a sparse index on player ID.

Answer

Use a local secondary index on score.

Answer

Enable DynamoDB Accelerator (DAX) for caching.

Question 4

A company uses AWS CodePipeline with CodeBuild to deploy a Node.js application. The build fails intermittently with 'npm ERR! network' errors. What is the most likely cause and solution?

Accepted Answer

The build environment lacks outbound internet access; configure a NAT gateway or use a VPC endpoint for npm.. Option A is correct because CodeBuild may have limited outbound internet access; using a NAT gateway or VPC endpoint for npm registry resolves this. Option B is incorrect because failing test does not cause network errors. Option C is incorrect because CodeBuild does not have npm cache. Option D is incorrect because npm token expiry returns 401, not network errors.

Answer

A unit test is failing; fix the test code.

Answer

The npm cache is corrupted; clear the cache in CodeBuild.

Answer

The npm token has expired; regenerate the token.

Question 5

A developer receives an AccessDeniedException when trying to invoke a Lambda function from an Amazon API Gateway REST API. The Lambda resource-based policy allows API Gateway. What is the most likely issue?

Accepted Answer

The API Gateway execution role lacks lambda:InvokeFunction permission.. Option C is correct because when API Gateway invokes a Lambda function, it must have the `lambda:InvokeFunction` permission. Even if the Lambda resource-based policy grants API Gateway access, the API Gateway execution role must also explicitly allow the `lambda:InvokeFunction` action. Without this permission, API Gateway cannot invoke the function, resulting in an AccessDeniedException.

Answer

The Lambda function is in a VPC without a NAT gateway.

Answer

The Lambda function concurrency limit is exceeded.

Answer

API Gateway caching is enabled, returning stale responses.

Question 6

A developer is optimizing costs for an S3 bucket that stores infrequently accessed data but requires millisecond retrieval. The bucket receives 100 PUT requests per second and 10 GET requests per second. Which storage class is most cost-effective?

Accepted Answer

S3 Intelligent-Tiering. S3 Intelligent-Tiering is the most cost-effective choice because it automatically moves objects between access tiers based on changing access patterns, optimizing costs without performance impact. The workload has a high write-to-read ratio (100 PUTs vs 10 GETs per second) and requires millisecond retrieval, which Intelligent-Tiering supports while avoiding the retrieval fees and minimum storage duration penalties of One Zone-IA or Glacier Deep Archive.

Answer

S3 Standard

Answer

S3 One Zone-IA

Answer

S3 Glacier Deep Archive

Question 7

A company runs a stateful web application on EC2 instances in an Auto Scaling group. Users report that their session data is lost when instances are replaced during scaling events. What is the best solution to preserve session state?

Accepted Answer

Use ElastiCache as a centralized session store.. ElastiCache provides a centralized, in-memory session store that is external to the EC2 instances. This ensures session data persists independently of the instance lifecycle, so when an instance is replaced during a scaling event, the new instance can retrieve the session from ElastiCache, preserving user state. This is the best solution because it decouples session state from compute resources, aligning with the stateless application pattern recommended for Auto Scaling groups.

Answer

Enable sticky sessions on the Application Load Balancer.

Answer

Store sessions in the Application Load Balancer.

Answer

Use an S3 bucket to store session data.

Question 8

A developer attaches the above bucket policy to an S3 bucket. An anonymous user tries to access https://my-bucket.s3.amazonaws.com/secret/key.txt. What is the result?

Accepted Answer

Access is denied because the explicit Deny overrides the Allow.. Option B is correct because the explicit Deny overrides the Allow. Even though the Allow grants access to all objects, the Deny for the secret/ prefix explicitly denies access. Option A is incorrect because the explicit Deny takes precedence. Option C is incorrect because the policy is valid. Option D is incorrect because the user is anonymous but the Deny applies.

Answer

Access is allowed because the Allow statement covers all objects.

Answer

Access is allowed because anonymous requests are not affected by Deny statements.

Answer

Access is denied because the policy is invalid (two statements conflict).

Question 9

An IAM user has the above policy attached. The user tries to stop an EC2 instance. What happens?

Accepted Answer

The stop operation succeeds.. Option A is correct because the Allow statement explicitly allows StopInstances for all resources. The Deny only applies to TerminateInstances, not StopInstances. Option B is incorrect because there is no Deny for StopInstances. Option C is incorrect because StopInstances is allowed. Option D is incorrect because the policy is valid.

Answer

The stop operation fails because ec2:StopInstances is not allowed explicitly.

Answer

The stop operation fails because of the Deny statement.

Answer

The stop operation fails because the policy is invalid (conflict).

Question 10

A developer runs the above CLI command to check a Lambda function's logs. The function is invoked but no logs appear in CloudWatch. The IAM role for the Lambda function has the AWSLambdaBasicExecutionRole managed policy attached. What is the most likely cause?

Accepted Answer

The log group's retention policy has deleted older logs.. Option C is correct because the log group exists (storedBytes >0) but retention is 30 days, so logs older than 30 days are deleted. The developer may be looking at a timeframe beyond retention. Option A is incorrect because the role has the necessary permissions (AWSLambdaBasicExecutionRole includes CreateLogGroup, CreateLogStream, PutLogEvents). Option B is incorrect because the function is being invoked (otherwise storedBytes would be 0). Option D is incorrect because storedBytes is not zero, indicating logs were written.

Answer

The CloudWatch Logs service is not enabled in the region.

Answer

The Lambda function's IAM role does not have permission to create log groups.

Answer

The Lambda function is not being invoked.

Question 11

Which TWO actions can help reduce Lambda cold start times? (Choose two.)

Accepted Answer

Increase the memory allocated to the function.. Option B is correct because increasing memory also increases CPU, which speeds up initialization. Option C is correct because using Provisioned Concurrency keeps environments warm. Option A is incorrect because larger deployment packages increase cold start. Option D is incorrect because VPC adds network overhead, increasing cold start. Option E is incorrect because reducing memory decreases CPU, worsening cold start.

Answer

Increase the deployment package size.

Answer

Place the function in a VPC.

Answer

Reduce the function timeout.

Question 12

Which THREE are valid methods to handle application configuration in AWS? (Choose three.)

Accepted Answer

AWS Secrets Manager. AWS Secrets Manager is a valid method for handling application configuration because it securely stores and manages sensitive configuration data such as database credentials, API keys, and other secrets. It supports automatic rotation of secrets, fine-grained access control via IAM policies, and integrates with AWS services like RDS, Redshift, and Lambda. This makes it ideal for managing dynamic configuration values that require high security and lifecycle management.

Answer

AWS CloudFormation template parameters

Answer

AWS IAM roles

Question 13

Which TWO are best practices for optimizing DynamoDB performance? (Choose two.)

Accepted Answer

Use SQS to decouple write-heavy workloads and handle spikes.. Option A is correct because using SQS to decouple write-heavy workloads allows DynamoDB to absorb traffic spikes by buffering writes in a queue, preventing throttling and enabling batch processing. This pattern, often called 'queue-based load leveling,' ensures that DynamoDB's provisioned capacity is not overwhelmed by sudden bursts, improving overall system resilience and cost efficiency.

Answer

Provision maximum write capacity units to handle any spike.

Answer

Use Scan operations instead of Query for retrieving data.

Answer

Enable strongly consistent reads for all read operations.

Question 14

A developer reports that an AWS Lambda function is timing out after 3 seconds. The function reads from an Amazon SQS queue. What is the most likely cause?

Accepted Answer

The Lambda function timeout is set to 3 seconds, which is too low.. The Lambda function is timing out after exactly 3 seconds because its configured timeout is set to 3 seconds, which is too low for the workload. Lambda has a maximum execution timeout of 15 minutes (900 seconds), but the default timeout is 3 seconds. Since the function reads from an SQS queue, it likely needs more time to process messages, and increasing the timeout value will resolve the issue.

Answer

The Lambda function memory is set too low, causing slow execution.

Answer

The Lambda execution role lacks permissions to poll SQS.

Answer

The SQS queue is empty, causing the function to wait indefinitely.

Question 15

An application running on Amazon ECS with Fargate is experiencing high latency. The application writes logs to Amazon CloudWatch Logs. Which AWS service can be used to analyze the logs to pinpoint the cause of the latency?

Accepted Answer

Amazon CloudWatch Logs Insights. Amazon CloudWatch Logs Insights is the correct choice because it is purpose-built for interactively querying and analyzing log data stored in CloudWatch Logs. It allows you to run SQL-like queries (using a query language) to filter, aggregate, and visualize log events, which is essential for pinpointing latency patterns, such as slow API calls or database queries, without needing to export logs to another service.

Answer

Amazon CloudWatch Logs

Answer

AWS X-Ray

Answer

Amazon S3