DVA-C02 Development with AWS Services Practice Test 10 — 15 Questions

Question 1

A company runs a production application on Amazon EC2 instances behind an Application Load Balancer (ALB). The application receives high traffic and needs to process incoming HTTP requests, store the request payload in an S3 bucket for auditing, and return a response. The development team uses AWS Lambda to process the payload. The team wants to ensure that the solution is scalable, fault-tolerant, and decoupled. The current approach is to have the EC2 instances send requests directly to the Lambda function via the AWS SDK. However, the team notices that during traffic spikes, some requests are lost and the Lambda function throttles. What should the team do to improve the architecture?

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

Accepted Answer

Have the EC2 instances send messages to an Amazon SQS queue, and configure the SQS queue as an event source for the Lambda function.. Using Amazon SQS decouples the EC2 instances from the Lambda function, providing a buffer that absorbs traffic spikes and prevents request loss. The SQS queue acts as an event source for Lambda, allowing the function to process messages at its own pace, reducing throttling. Option A is incorrect because increasing reserved concurrency may reduce throttling but does not buffer requests; if the function is still overwhelmed, requests can be dropped. Option B is incorrect because API Gateway still invokes Lambda synchronously, and throttling can still occur. Option C is incorrect because Kinesis Data Streams is designed for real-time streaming and analytics, not for simple request queuing, and introduces unnecessary complexity.

Answer

Increase the Lambda function's reserved concurrency to the maximum allowed.

Answer

Place API Gateway in front of Lambda and have EC2 send requests to API Gateway.

Answer

Use Amazon Kinesis Data Streams instead of Lambda to process the payload.

Question 2

Refer to the exhibit. A developer created the CloudFormation template snippet. After deployment, the developer uploads a file to the bucket, but the Lambda function is not invoked. What is the MOST likely cause?

Answer

The bucket has a bucket policy that denies s3:PutObject for the IAM user.

Answer

The bucket has versioning enabled, which blocks event notifications.

Answer

The lifecycle rule moves objects to Glacier before the notification is sent.

Answer

The Lambda function returned an error, so the invocation failed silently.

Question 3

A developer is building a serverless application that uses AWS Step Functions to orchestrate multiple AWS Lambda functions. The workflow involves three steps: validate input, process data, and store results. The developer notices that the workflow occasionally fails due to transient errors in the process data step. The developer wants to implement error handling so that the workflow retries the process data step up to three times with an exponential backoff. Additionally, if all retries fail, the workflow should send a notification to an Amazon SNS topic and transition to a failure state. The developer has defined the state machine in Amazon States Language (ASL). How should the developer configure the state machine?

Accepted Answer

In the process data state definition, add a Retry field with MaxAttempts: 3 and BackoffRate: 2, and add a Catch field that transitions to a failure state and sends an SNS notification.. In Amazon States Language, you define Retry and Catch fields within a state to handle errors. The Retry field with MaxAttempts: 3 and BackoffRate: 2 implements exponential backoff. The Catch field catches errors after retries are exhausted and can transition to a failure state while sending an SNS notification. Option A is incorrect because the retry logic should be defined in the state machine using ASL, not in the Lambda function code. Option B is incorrect because modifying the IAM role is necessary for SNS permissions but does not configure retry behavior; ResultPath is used for input/output handling, not error handling. Option D is incorrect because Retry and Catch must be defined per state, not at the workflow level.

Answer

Write custom retry logic inside the Lambda function code and catch exceptions there.

Answer

Modify the IAM execution role to allow the state machine to call SNS and then use a ResultPath to handle errors.

Answer

Add a Retry field at the workflow level and a Catch field at the workflow level.

Question 4

A company is using Amazon DynamoDB as the database for a web application. The application reads and writes items based on a primary key. The traffic pattern shows that reads are 10 times more frequent than writes. The development team wants to reduce read latency and costs. They are considering adding a cache layer. The data is not sensitive, but stale data is acceptable for up to 5 minutes. The application runs on EC2 instances. What should the team do to implement caching?

Accepted Answer

Set up an Amazon ElastiCache Memcached cluster and update the application to check the cache before reading from DynamoDB.. Amazon ElastiCache with Memcached is a distributed in-memory cache that can significantly reduce read latency for read-heavy workloads. By checking the cache before reading from DynamoDB, the application can serve frequent reads from ElastiCache, reducing load on DynamoDB and lowering costs. The allowable stale data of up to 5 minutes can be accommodated by setting a TTL on cached items. Option A, DAX, is also a caching solution but it is tightly integrated with DynamoDB and can be more expensive and less flexible than ElastiCache for this use case where cost reduction is a goal. Option B, storing data in S3, introduces higher latency and is not designed for low-latency caching of database queries. Option D, CloudFront, is a content delivery network for caching static assets at edge locations and does not reduce latency for database queries from the application.

Answer

Use Amazon DynamoDB Accelerator (DAX) as a caching layer.

Answer

Store frequently accessed items in an S3 bucket and read from S3.

Answer

Use Amazon CloudFront to cache responses from the application.

Question 5

A developer attached the above IAM policy to an IAM user. The user tries to upload an object to the S3 bucket my-bucket without specifying server-side encryption. What will happen?

Accepted Answer

The upload will be denied because the Deny statement explicitly denies PutObject without AES256 encryption.. The question stem refers to an IAM policy ('the above IAM policy') but no policy is provided in the prompt. The policy JSON must be included in the stem for the question to be answerable.

Answer

The upload will succeed because the Deny statement is redundant.

Answer

The upload will succeed because the Allow statement grants PutObject permission.

Answer

The upload will succeed but the object will be stored without encryption.

Question 6

A Lambda function processes messages from an SQS queue. The function occasionally fails due to network timeouts when calling an external API. The developer wants to retry failed messages automatically. What should the developer do?

Accepted Answer

Configure a dead-letter queue for the SQS queue and set the Lambda function's maximum retries to 2.. When Lambda processes messages from an SQS queue, it polls the queue synchronously. If the Lambda function fails or times out, the message is returned to the queue and retried automatically once the visibility timeout expires. To limit the number of retries and handle failed messages safely, you must configure a Dead-Letter Queue (DLQ) on the SQS queue itself using a redrive policy with a specified 'maxReceiveCount'. Lambda's own retry settings and Lambda-level DLQs only apply to asynchronous invocations, not to SQS event source mappings.

Answer

Enable SQS redrive policy to automatically retry after a failure.

Answer

Configure a dead-letter queue on the Lambda function to capture failed events.

Answer

Increase the Lambda function's timeout to 15 minutes.

Question 7

A developer is deploying a new version of an AWS Lambda function using the AWS CLI. The developer wants to ensure that the new version is stable before routing all traffic to it. The developer has already published version 1 and version 2 of the function. The developer wants to send 10% of the traffic to version 2 and 90% to version 1. The developer then plans to gradually increase the traffic to version 2. Which approach should the developer use?

Accepted Answer

Create a Lambda alias named 'prod' and update the alias's routing configuration to send 10% traffic to version 2 and 90% to version 1.. Lambda aliases support traffic shifting via weighted routing. Option A is incorrect because Lambda function versions do not support traffic weights directly. Option C is incorrect because there is no built-in feature to configure traffic distribution on the function itself. Option D is incorrect because creating a new alias does not automatically route traffic to it; the alias must be used as the invocation target, and updating an existing alias (as in option B) is the standard approach to gradually shift traffic.

Answer

Use the Lambda function's versioning feature to set the traffic weight directly on the function.

Answer

Configure the API Gateway endpoint to route 10% of requests to version 2 and 90% to version 1.

Answer

Create a new alias and assign the traffic weights to the versions in the alias configuration.

Question 8

A developer is deploying a serverless application using AWS SAM. The application includes an API Gateway endpoint that invokes a Lambda function. The developer wants to pass a stage name as a parameter to the Lambda function. How should the developer define the Lambda function's environment variable in the SAM template?

Accepted Answer

Use the parameter reference 'Ref: StageName' in the environment variable mapping.. The `Ref: StageName` references a parameter defined in the SAM template, which can be passed as an environment variable to the Lambda function. This allows dynamic stage names instead of hardcoding. Option B is wrong because hardcoding 'Stage: dev' defeats the purpose of parameterization. Option C is wrong because `Fn::GetAtt` is used to retrieve attributes of resources, not parameter values. Option D is wrong because `Fn::ImportValue` is for cross-stack references, not for template parameters.

Answer

Define the environment variable as 'Stage: dev' in the Lambda function configuration.

Answer

Use 'Fn::GetAtt: [AWS::StackName, Outputs.StageName]' to get the stage name.

Answer

Use 'Fn::ImportValue: StageName' to import from another stack.

Question 9

A developer is writing a Lambda function that processes events from an Amazon Kinesis stream. The function must ensure that records are processed in the order they were received and that each shard is processed by only one instance of the function at a time. How should the developer configure the Lambda function?

Accepted Answer

Set the function's concurrency to the number of shards and enable parallelization factor.. By default, the Amazon Kinesis event source mapping for AWS Lambda processes records sequentially within each shard. It guarantees that records are processed in the order they were received and that only one instance of the Lambda function processes a given shard at any one time. Enabling a parallelization factor (greater than 1) would allow multiple instances of the function to process different batches from the same shard concurrently, which violates the requirement. Setting the reserved concurrency to 1 is a severe anti-pattern because it limits the entire Lambda function to a single concurrent execution across all shards, causing massive processing delays if the stream has multiple shards.

Answer

Set the batch size to 1 and configure the function's reserved concurrency to 1.

Answer

Set the batch size to 100 and enable parallelization factor per shard.

Answer

Use a DynamoDB table to track sequence numbers and enforce ordering.

Question 10

A developer is reviewing a CloudFormation template that creates an S3 bucket and a Lambda function. The Lambda function's code is stored in the S3 bucket. What is a potential issue with this template?

Accepted Answer

The Lambda function depends on the S3 bucket, but there is no DependsOn clause to ensure the bucket is created first.. When CloudFormation creates the S3 bucket, the bucket is initially empty. Since the Lambda function creation happens in the same deployment and references the bucket, CloudFormation will attempt to retrieve the zip file specified in the `S3Key` property immediately after the bucket is created. Because the zip file has not been uploaded yet, the Lambda creation will fail with a 'NoSuchKey' (or 'Access Denied') error. To resolve this, developers typically use a pre-existing S3 bucket for Lambda deployments, or use inline code (`ZipFile`) for simple functions.

Answer

The Lambda function's role is referenced incorrectly; it should be 'Ref' instead of 'GetAtt'.

Answer

The bucket name 'my-unique-bucket-12345' is not globally unique.

Answer

The bucket must have versioning enabled to store Lambda code.

Question 11

A developer attaches this IAM policy to an IAM user. The user tries to upload an object to the S3 bucket my-bucket from an IP address of 10.0.1.5. What will happen?

Accepted Answer

The upload will fail because the IP address is not within the allowed range.. The stem refers to an IAM policy ('A developer attaches this IAM policy...'), but no policy document is provided in the question. Without the policy document, the question cannot be answered or verified.

Answer

The upload will fail because the bucket policy denies access.

Answer

The upload will succeed because the policy allows s3:PutObject.

Answer

The upload will succeed because the condition is ignored for uploads.

Question 12

A developer is designing a serverless application that uses Amazon API Gateway and AWS Lambda. The API receives a high volume of requests, and the developer needs to cache responses to reduce latency and cost. Which TWO actions should the developer take? (Choose TWO.)

Accepted Answer

Use Amazon CloudFront in front of API Gateway to cache responses.. To cache responses from an API Gateway and Lambda serverless application, developers have two primary options:
1. **Enable API Gateway caching (Option D):** This caches responses at the API Gateway stage level, reducing the number of executions of the backend Lambda function, which lowers both latency and cost.
2. **Use Amazon CloudFront in front of API Gateway (Option C):** CloudFront can cache API responses at edge locations. This is often more cost-effective than API Gateway's built-in caching and further reduces latency by serving content closer to the users.

Option E is incorrect because returning `Cache-Control` headers from Lambda does not enable caching on the server side unless a caching layer like CloudFront is configured in front of it. Option A (DAX) is used for DynamoDB caching, and Option B (ElastiCache) requires custom application code and is more complex to manage.

Answer

Use DynamoDB Accelerator (DAX) to cache Lambda responses.

Answer

Use ElastiCache for Redis to store frequently accessed responses.

Answer

Configure the Lambda function to return cache-control headers in the response.

Question 13

A company is deploying a containerized application on Amazon ECS using the Fargate launch type. The application must be highly available across multiple Availability Zones. The developer needs to configure the ECS service. Which THREE configuration options are required? (Choose THREE.)

Accepted Answer

Set the desired number of tasks to at least 2.. To achieve high availability across multiple Availability Zones for an ECS service using the Fargate launch type, you must:
1. **Set the desired number of tasks to at least 2 (Option B):** Running a single task represents a single point of failure. Having at least 2 tasks allows them to be distributed across different AZs.
2. **Configure the service to place tasks in at least two subnets in different Availability Zones (Option D):** This ensures that ECS launches the tasks in separate physical locations, protecting the application against an AZ outage.
3. **Associate an Application Load Balancer with the ECS service (Option C):** An ALB is required to distribute incoming traffic across the tasks running in different AZs and to perform health checks, routing traffic away from any failed tasks.

**Why other options are incorrect:**
- **Option A is incorrect:** Auto Scaling groups (ASGs) are used for the EC2 launch type to manage the underlying EC2 instances. Fargate is serverless and does not use ASGs.
- **Option E is incorrect:** Storing task state in DynamoDB is an application-level design choice for statelessness, but it is not a configuration option of the ECS service itself to achieve high availability.

Answer

Create an Auto Scaling group for the Fargate tasks.

Answer

Use a DynamoDB table to store task state.

Question 14

A company is using AWS Lambda to process events from an SQS queue. The Lambda function runs for an average of 45 seconds and processes approximately 100 messages per second. The company notices that the Lambda function is being throttled, causing messages to remain in the queue for longer than expected. Which action would MOST effectively reduce throttling?

Accepted Answer

Increase the batch size in the Lambda event source mapping.. With 100 messages per second and an average execution time of 45 seconds, the required concurrency is 100 * 45 = 4,500 concurrent executions (assuming a batch size of 1). Since the default AWS Lambda concurrency limit per region is 1,000, the function will inevitably be throttled. Increasing the reserved concurrency (Option A) cannot exceed the account limit and would not solve the issue. By increasing the batch size in the event source mapping (Option C), each Lambda invocation processes multiple messages, which significantly reduces the number of concurrent executions required to handle the same message volume, thereby effectively eliminating the throttling.

Answer

Increase the reserved concurrency for the Lambda function.

Answer

Increase the number of shards for the SQS queue.

Answer

Configure a Dead Letter Queue for the SQS queue.

Question 15

A developer is using the AWS CLI to upload a large file to S3. The file is 2 GB. The developer uses the following command: aws s3 cp largefile.zip s3://mybucket/. The upload is taking longer than expected. Which change would MOST improve the upload speed?

Accepted Answer

Enable S3 Transfer Acceleration on the bucket and use the --endpoint-url parameter.. S3 Transfer Acceleration (S3TA) is designed to maximize transfer speeds for large objects by routing traffic through Amazon CloudFront's globally distributed edge locations. To use S3 Transfer Acceleration with the AWS CLI, you must first enable it on the S3 bucket and then direct your CLI commands to the accelerated endpoint (e.g., by using the `--endpoint-url` parameter pointing to the `.s3-accelerate.amazonaws.com` endpoint or by enabling `use_accelerate_endpoint` in the CLI configuration).

Answer

Disable multipart upload by setting --no-multipart.

Answer

Increase the multipart upload part size using the --multipart-upload-part-size option.

Answer

Use the aws s3api put-object command instead.