DVA-C02 Troubleshooting and Optimization Practice Test 17 — 15 Questions

Question 1

A developer is troubleshooting a CloudFront distribution that serves static content from an S3 bucket. Users in some geographic locations report slow load times. The developer checks the CloudFront metrics and sees a high number of cache misses. What is the MOST likely cause?

Accepted Answer

The object TTL is set to a very low value (e.g., 0 seconds).. Option B is correct because a short TTL causes objects to expire from edge caches quickly, leading to frequent cache misses and requests going back to the origin. Option A (price class) affects edge locations but not cache hits. Option C (compression) does not affect cache hits. Option D (signed URLs) would cause misses if URLs are not properly constructed but not high miss rate.

Answer

The CloudFront distribution is configured with Price Class 100, which uses only the US and Europe edge locations.

Answer

The S3 bucket is configured with signed URLs for access.

Answer

The CloudFront distribution is not configured to compress objects.

Question 2

A developer is investigating why an Amazon API Gateway REST API is returning 504 errors during peak traffic. The API integrates with a Lambda function. Which TWO factors are MOST likely causing the 504 errors? (Choose TWO.)

Accepted Answer

The Lambda function is hitting its reserved concurrency limit and being throttled.. Option A and Option B are correct. Option A: If the Lambda function's timeout is less than the API Gateway integration timeout (29 seconds), the function may timeout before the API Gateway, causing a 504. Option B: If the Lambda function is throttled, API Gateway receives a 429 from Lambda and returns a 504. Option C (API Gateway throttling) would cause 429, not 504. Option D (cache) would not cause 504. Option E (WAF) would cause 403.

Answer

The API Gateway cache is full and cannot store responses.

Answer

The AWS WAF is blocking the request.

Answer

The API Gateway account-level throttling limits are exceeded.

Question 3

A developer is optimizing an application that uses Amazon DynamoDB. The application reads items by primary key and also performs queries on a Global Secondary Index (GSI). The developer notices that some queries on the GSI are slow. Which TWO actions would improve the performance of GSI queries? (Choose TWO.)

Accepted Answer

Use a more distributed GSI partition key to avoid hot partitions.. Option A and Option B are correct. Option A: If the GSI is sparse (not all items have the GSI key attribute), the index may not have enough data to distribute reads; adding a filter condition can help. Actually, ensuring that the GSI key attribute exists on all items that need to be queried can improve performance. Option B: Overloading the GSI partition key can cause hot partitions; using a more distributed key pattern helps. Option C (adjust write capacity) does not directly help read performance on GSI. Option D (use strong consistency) would actually increase latency. Option E (increase read capacity) could help if the issue is throttling, but the question asks for two actions. Let me reconsider: The correct options should be: B (use a more distributed GSI partition key) and E (increase read capacity on the index) if the issue is throttling. However, increasing read capacity on the index is not directly possible; you increase read capacity on the table, which is shared with GSIs. Actually, GSIs use the same read capacity units as the table. So option E is not accurate. Option C says 'Increase the write capacity of the table' which would not help read performance. Option D 'Use strongly consistent reads' would be slower. So the best two are: B (redistribute keys) and A (ensure GSI key attribute exists on queried items) to avoid sparse index. Let me adjust the correct answers.

Answer

Increase the read capacity of the GSI.

Answer

Use strongly consistent reads on the GSI.

Answer

Increase the write capacity of the DynamoDB table.

Question 4

A company is using Amazon ElastiCache for Redis to improve the performance of a high-traffic web application. Recently, the application has been experiencing increased latency. The developer suspects that cache misses are causing the application to read from the database more frequently. Which THREE metrics should the developer examine in Amazon CloudWatch to troubleshoot this issue? (Choose THREE.)

Accepted Answer

CacheMisses. Option A, option B, and option C are correct. Option A: CacheMisses shows the number of requests that did not find a key in the cache. Option B: Evictions indicates keys removed due to memory pressure, which can cause increased misses. Option C: CurrConnections helps understand if there is a connection bottleneck. Option D (CPUUtilization) is not directly related to cache efficiency. Option E (SwapUsage) indicates memory pressure, which is related to evictions, but CPU is not the best metric for this issue. The three best are CacheMisses, Evictions, and CurrConnections.

Answer

SwapUsage

Answer

CPUUtilization

Question 5

A developer is deploying a web application on Amazon ECS with Fargate. The application needs to store session state. Which THREE options are suitable for storing session state in a distributed environment? (Choose THREE.)

Accepted Answer

Amazon RDS for MySQL. Option A, option C, and option D are correct. Option A: ElastiCache for Redis is commonly used for session storage. Option C: DynamoDB is a good choice for session state due to low latency and scalability. Option D: RDS for MySQL can be used but is less common due to relational overhead; however, it is still a valid option. Option B (local ephemeral storage) is not suitable because it is not shared across tasks. Option E (S3) is not designed for frequent read/write session data; it is object storage with higher latency.

Answer

Amazon S3

Answer

Local ephemeral storage on the Fargate task

Question 6

A developer has attached the IAM policy shown in the exhibit to a user. The user reports that they can upload and delete objects in the bucket 'my-bucket', but cannot list the objects in the bucket. What is the MOST likely reason?

Accepted Answer

The bucket has a bucket policy that denies s3:ListBucket.. Option A is correct. The ListBucket permission is granted at the bucket level (arn:aws:s3:::my-bucket), but the condition that the user must have s3:ListBucket permission is granted. However, the issue is that the user cannot list objects. The policy looks correct. The most common reason for being unable to list objects despite having ListBucket permission is that the bucket policy denies listing, or the user is trying to list a specific prefix without proper permissions. But in this case, the policy allows ListBucket on the bucket. Option B: The user is using an incorrect API call (e.g., ListObjectsV2) is unlikely. Option C: The bucket is in a different region would not affect permissions. Option D: The user needs s3:GetObject to list? No, listing requires ListBucket. So the correct answer is that the bucket policy overrides the IAM policy. Let me adjust: Actually, the most likely reason is that the bucket has a bucket policy that denies s3:ListBucket. That is option A. Yes.

Answer

The IAM policy is missing the s3:GetObject permission for listing.

Answer

The user is using the ListObjectsV2 API call instead of ListObjects.

Answer

The bucket is in a different region than the default region configured in the AWS CLI.

Question 7

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'?

Accepted Answer

The function code threw an uncaught exception.. Option B is correct. 'Unhandled' indicates that the function threw an exception that was not caught by the code, and the error was not mapped to a custom error response. Option A: If the function timed out, it would return a 200 status but with 'FunctionError' set to 'Unhandled' or 'Handled'? Actually, timeout results in 200 with 'FunctionError' set to 'Unhandled'. But the most common unhandled error is an uncaught exception. Option C (permissions) would cause a 403 error. Option D (payload size) would cause a 413 error.

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 8

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.. Option B is correct because 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 (region) is not true; bucket names are global. Option C (permissions) would cause a different error. Option D (template format) is valid JSON.

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 9

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.. Option C is correct because the Lambda function timeout is set to 3 seconds by default, causing the timeout error. Option A is wrong because VPC configuration does not cause timeout logs about 'Task timed out' - that message specifically refers to the function timeout. Option B is wrong because the function has no reserved concurrency issue. Option D is wrong because the logs indicate 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 10

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.. Option B is correct because a 502 from ALB indicates the target (EC2) closed the connection before the ALB could finish writing the request or reading the response. Option A is wrong because security groups blocking traffic would result in 503 or timeout. Option C is wrong because ALB health checks failing would cause 503. Option D is wrong because DNS resolution is not involved in ALB-to-target communication.

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 11

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.. Option D is correct because it transitions to S3 Standard-IA after 30 days (when access becomes rare) and to S3 Glacier Deep Archive after 90 days (for long-term compliance with lowest cost). Option A is wrong because S3 One Zone-IA is less durable. Option B is wrong because S3 Glacier Flexible Retrieval is more expensive than Deep Archive for long-term storage. Option C is wrong because S3 Intelligent-Tiering has monitoring costs and is not needed if access patterns are known.

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 12

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.. Option B is correct because throttling occurs when writes exceed provisioned WCU on the table, not the GSI. Option A is wrong because hot partition would cause throttling on specific partitions, but the scenario mentions general throttling. Option C is wrong because GSI throttling would affect writes to the GSI, not the table. Option D is wrong because adaptive capacity would mitigate throttling, not cause it.

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 13

A developer is troubleshooting a CloudFormation stack that fails to create. The stack includes an Auto Scaling group with a launch template. The error message says 'Value (null) for parameter groupId is invalid.' What is the MOST likely cause?

Accepted Answer

The launch template references a SecurityGroupId parameter that is not provided or is misspelled.. The error 'Value (null) for parameter groupId is invalid' indicates that a SecurityGroupId parameter referenced in the launch template is either not provided or misspelled. CloudFormation resolves parameters at stack creation; if the parameter is missing or has a typo, it evaluates to null, causing the launch template to fail validation because a security group ID is required for the network interface.

Answer

The Auto Scaling group does not specify a VPC subnet.

Answer

The Auto Scaling group's user data script contains a syntax error.

Answer

The launch template specifies an invalid key pair name.

Question 14

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.. Option D is correct because the health check path is set to HTTP port 80 by default, but the application may be listening on a custom port. Option A is wrong because if the application is not deployed, the error would be different. Option B is wrong because the health check error is about the target, not the load balancer. Option C is wrong because the security group would block all traffic, not just health checks.

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 15

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.. Option B is correct because using provisioned concurrency keeps the function initialized and warm, eliminating cold starts. Option A is wrong because increasing memory does not directly reduce cold start time. Option C is wrong because using the AWS SDK alone does not reduce cold starts. Option D is wrong because using a Node.js function would reduce cold starts but may require rewriting the code, which is not as effective as provisioned concurrency.

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.