DVA-C02 Troubleshooting and Optimization Practice Test 16 — 15 Questions

Question 1

A Lambda function reading from Kinesis is falling behind. Which two metrics/settings should be reviewed first?

Accepted Answer

IteratorAge for the event source mapping. The IteratorAge metric measures how far behind the Lambda function is in processing records from the Kinesis stream. A high IteratorAge indicates the function is falling behind, making it the primary metric to review. The batch size, parallelization factor, and shard count directly control the concurrency and throughput of the event source mapping, so adjusting these settings can help catch up.

Answer

S3 bucket public access settings

Answer

Route 53 hosted zone count

Question 2

Users receive AccessDenied when downloading SSE-KMS encrypted S3 objects cross-account. Which two policies may need changes?

Accepted Answer

S3 bucket/object access policy or IAM policy. When accessing SSE-KMS encrypted S3 objects cross-account, the S3 bucket policy or the IAM policy must explicitly grant the s3:GetObject permission to the caller. Additionally, the KMS key policy must allow the kms:Decrypt action for the caller's AWS account or IAM role, because SSE-KMS uses a customer master key (CMK) to encrypt the object, and decryption requires KMS permissions. Without both policies, the request fails with AccessDenied even if the S3 permissions are correct.

Answer

CloudFront cache policy

Answer

Route 53 resolver rule policy

Question 3

Drag and drop the steps to authenticate a user using Amazon Cognito User Pools in the correct order.

Accepted Answer

Create the user pool and app client, then authenticate to receive tokens, then use tokens for authorization.. First create the user pool and app client, then authenticate to receive tokens, and use tokens for authorization.

Answer

Authenticate to receive tokens, then create the user pool and app client, then use tokens for authorization.

Answer

Create the user pool and app client, then use tokens for authorization, then authenticate to receive tokens.

Answer

Use tokens for authorization, then create the user pool and app client, then authenticate to receive tokens.

Question 4

Match each AWS storage class to its description.

Accepted Answer

S3 Standard: Designed for frequently accessed data with low latency and high throughput.. The correct matches are S3 Standard with frequently accessed data, S3 Intelligent-Tiering with automatic cost optimization, S3 Glacier Instant Retrieval with archive and fast retrieval, and S3 One Zone-IA with infrequent data in one AZ. Common confusions include mixing up storage class descriptions.

Answer

S3 Standard: Infrequent access data stored in a single Availability Zone.

Answer

S3 Intelligent-Tiering: Archive storage with retrieval times of minutes.

Question 5

Match each AWS deployment strategy to its description.

Accepted Answer

Rolling deployment: Incrementally replaces instances of the previous version with new version instances.. Common deployment strategies include Rolling, Blue/Green, and Canary. Rolling deploys incrementally, Blue/Green switches between environments, and Canary tests with a small subset. Distractors often confuse these definitions.

Answer

Rolling deployment: Simultaneously updates all instances.

Answer

Canary deployment: Deploys to a full separate environment and then switches traffic.

Question 6

A developer is troubleshooting a web application that intermittently returns HTTP 504 errors. The application runs on EC2 instances behind an Application Load Balancer. What is the most likely cause of these errors?

Accepted Answer

The load balancer idle timeout is set too low, and the application takes longer than the timeout to respond.. HTTP 504 (Gateway Timeout) errors from an Application Load Balancer indicate that the load balancer successfully connected to the target (EC2 instance) but the target did not respond within the configured idle timeout period. The default idle timeout is 60 seconds, and if the application's processing time exceeds this value, the load balancer terminates the connection and returns a 504. Option C directly addresses this mismatch between the load balancer timeout and the application response time.

Answer

The target group is using an HTTPS health check but the instances only support HTTP.

Answer

The load balancer's cross-zone load balancing is disabled.

Answer

The security group for the EC2 instances is missing an inbound rule for the load balancer.

Question 7

A Lambda function processing SQS messages is failing with concurrency errors. The function is configured with reserved concurrency of 5. The SQS queue has a batch size of 10. What is the most effective way to prevent throttling?

Accepted Answer

Increase the reserved concurrency to a higher value.. The function is throttling due to insufficient reserved concurrency. With a batch size of 10, each SQS batch triggers one invocation, but the function's reserved concurrency of 5 limits concurrent executions to 5. Increasing reserved concurrency allows more concurrent invocations to handle the SQS messages without throttling.

Answer

Reduce the batch size to 1 to spread out invocations.

Answer

Increase the Lambda function memory to get more concurrency.

Answer

Set the SQS queue's concurrency limit to match the Lambda reserved concurrency.

Question 8

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.. 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 9

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 10

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 11

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 12

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.. The explicit Deny statement for the 'secret/' prefix overrides the Allow statement that grants access to all objects. Even though the Allow grants access to all objects, the Deny specifically denies access to objects under 'secret/', and explicit Deny always takes precedence. Option B is incorrect because the Deny overrides the Allow for the specified prefix. Option C is incorrect because Deny statements apply to all users, including anonymous users. Option D is incorrect because having two statements that conflict does not make the policy invalid; the explicit Deny simply takes precedence.

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 13

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

Accepted Answer

Increase the memory allocated to the function.. 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 the function timeout does not affect cold start time; timeout limits execution duration, not initialization.

Answer

Increase the deployment package size.

Answer

Place the function in a VPC.

Answer

Reduce the function timeout.

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