DVA-C02 Development with AWS Services Practice Test 14 — 15 Questions

Question 1

A Lambda function processes messages from an SQS standard queue and writes results to DynamoDB. Duplicate writes occasionally occur after retries. Which two changes best make the processing idempotent?

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

Accepted Answer

Use a deterministic idempotency key stored with a conditional write in DynamoDB. Using a deterministic idempotency key (e.g., a business transaction ID) combined with a conditional write in DynamoDB ensures that if the same message is processed more than once, the second write attempt will fail because the item already exists. This prevents duplicate records even when Lambda retries after a failure or timeout, making the processing idempotent at the database level.

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Increase the Lambda timeout to 15 minutes

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Disable SQS visibility timeout

Question 2

An API Gateway REST API invokes Lambda synchronously. Clients receive 502 responses after a deployment, but Lambda logs show a successful business operation. What is the most likely issue?

Accepted Answer

The Lambda proxy integration response format is invalid. Lambda proxy integration requires the response to be in a specific JSON format: `{"statusCode": ..., "headers": ..., "body": ...}`. If the Lambda function returns a plain string or an object missing these keys, API Gateway cannot map it to an HTTP response, resulting in a 502 Internal Server Error. The successful business operation in logs confirms the Lambda code ran correctly, but the malformed response format causes the gateway error.

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The Lambda execution role lacks dynamodb:PutItem

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The API cache TTL is too short

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The API stage has X-Ray tracing enabled

Question 3

A Step Functions workflow calls three independent Lambda functions and should continue only after all results are available. Which state pattern should be used?

Accepted Answer

Parallel state. The Parallel state in AWS Step Functions is designed to execute multiple branches of work concurrently and then aggregate their outputs into a single array. This is exactly what is needed when three independent Lambda functions must all complete before the workflow continues, as the Parallel state waits for all branches to finish before proceeding to the next state.

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Choice state

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Wait state

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Fail state

Question 4

A developer needs an S3 upload workflow where clients upload large files directly to S3 without exposing AWS credentials through the browser. What should the backend generate?

Accepted Answer

Pre-signed URLs with appropriate expiration and object restrictions. Pre-signed URLs allow the backend to generate time-limited, permission-restricted URLs that clients can use to upload objects directly to S3 without exposing AWS credentials. The backend signs the URL with IAM credentials, and the client uses the URL to perform the PUT operation, ensuring secure, credential-free uploads.

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Long-lived IAM access keys for each client

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A public-read bucket policy

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An S3 Inventory report

Question 5

A DynamoDB table uses partition key customerId. One enterprise customer generates most traffic and is throttled while the table has unused capacity elsewhere. What design change best addresses the hot partition?

Accepted Answer

Add write sharding or redesign the partition key to distribute that customer's workload. The hot partition is caused by a single customerId receiving a disproportionate amount of traffic, exceeding the 3000 RCU or 1000 WCU per partition limit. By adding write sharding (e.g., appending a random suffix to the partition key) or redesigning the partition key to include a more granular attribute, you distribute that customer's writes across multiple partitions, eliminating the bottleneck and utilizing the table's unused capacity.

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Enable point-in-time recovery

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Reduce item size by removing attributes

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Use strongly consistent reads only

Question 6

A Lambda function receives events from EventBridge. The developer wants failed invocations to be retried and then stored for later analysis if retries are exhausted. Which configuration should be used?

Accepted Answer

Configure EventBridge retry policy and a dead-letter queue. EventBridge supports a configurable retry policy (with a maximum event age up to 24 hours and up to 185 retries by default) and can route events that exceed the retry limit to an Amazon SQS dead-letter queue (DLQ). This ensures failed invocations are retried automatically and, if all retries are exhausted, the event is stored durably in the DLQ for later analysis or reprocessing.

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Enable API Gateway access logging

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Increase reserved concurrency to zero

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Store events in CloudFormation outputs

Question 7

A service publishes order events to SNS. Several consumers need different filtered subsets of events without changing publisher code. What should the developer configure?

Accepted Answer

SNS subscription filter policies. SNS subscription filter policies allow each consumer to define a JSON policy on their subscription that selectively delivers only messages matching specified attributes (e.g., event type, region). This enables multiple consumers to receive different filtered subsets of the same SNS topic without modifying the publisher's code, as the filtering happens server-side at the SNS service level.

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Separate AWS accounts for each consumer

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Lambda code that discards unwanted events after invocation

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SQS long polling only

Question 8

A Lambda function must retrieve feature flags at runtime with low latency and controlled rollout. Which AWS service is most appropriate?

Accepted Answer

AWS AppConfig. AWS AppConfig is the correct choice because it is purpose-built for managing application configuration at runtime, including feature flags, with support for controlled rollouts (e.g., percentage-based deployments, canary releases) and low-latency retrieval via the AppConfig agent or direct API calls. It integrates with AWS Lambda to fetch configuration values on-demand without requiring a full deployment, enabling dynamic feature toggling.

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AWS CloudFormation Parameters

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AWS IAM Access Analyzer

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Amazon Inspector

Question 9

A developer uses the AWS SDK to list thousands of DynamoDB items from a query. Only the first page is processed. What should be implemented?

Accepted Answer

Pagination using LastEvaluatedKey until no further key is returned. The DynamoDB Query API returns paginated results, with a maximum of 1 MB of data per page. The `LastEvaluatedKey` in the response indicates that more items exist. To retrieve all items, the application must check for `LastEvaluatedKey` and, if present, issue a subsequent Query request with the `ExclusiveStartKey` parameter set to that value, repeating until `LastEvaluatedKey` is no longer returned. This is the standard pagination pattern for DynamoDB.

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A larger Lambda memory setting only

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A global secondary index with the same key

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Strongly consistent reads on every request

Question 10

A developer wants exactly-once processing semantics for commands submitted to a queue where duplicate command IDs must be rejected within five minutes. Which SQS feature is most directly relevant?

Accepted Answer

FIFO queue deduplication ID. FIFO queues support exactly-once processing by using a deduplication ID. When a message with a given deduplication ID is sent, SQS automatically rejects any duplicate within a 5-minute deduplication interval. This directly meets the requirement to reject duplicate command IDs within five minutes.

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Standard queue delay seconds

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Dead-letter queue redrive policy

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Visibility timeout extension

Question 11

A Lambda function must share reusable validation code across several functions without packaging the same library into every deployment artifact. What should be used?

Accepted Answer

Lambda layer. Lambda layers allow you to centrally manage reusable code (e.g., validation libraries) and share it across multiple Lambda functions without packaging it into each deployment artifact. When you attach a layer to a function, the layer's content is extracted into the /opt directory, making it available at runtime. This avoids duplication and simplifies updates, as you only need to update the layer version rather than every function's deployment package.

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API Gateway usage plan

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S3 multipart upload

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CloudWatch metric filter

Question 12

An application uses DynamoDB Streams to trigger downstream processing. The processor must receive both old and new item images after updates. Which stream view type should be configured?

Accepted Answer

NEW_AND_OLD_IMAGES. B is correct because DynamoDB Streams must be configured with the NEW_AND_OLD_IMAGES stream view type to capture both the item's state before and after a write operation (update, insert, or delete). This ensures the downstream processor receives the complete old and new item data, which is required for use cases like auditing, change data capture, or reconciling state changes.

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KEYS_ONLY

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NEW_IMAGE only

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OLD_IMAGE only

Question 13

A REST API requires request validation before invoking Lambda to reduce unnecessary function executions for malformed payloads. Where should validation be configured?

Accepted Answer

In API Gateway request models and validators. API Gateway provides built-in request validation using models (JSON Schema) and validators. By configuring validation at the API Gateway layer, malformed payloads are rejected before they reach the Lambda function, reducing unnecessary invocations and associated costs. This is the correct approach because API Gateway acts as the entry point for REST APIs and can enforce payload structure without invoking the backend.

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Inside the Lambda timeout setting

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In the IAM execution role

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In the S3 bucket policy

Question 14

A developer wants a Lambda function to process SQS messages in batches but avoid losing the whole batch when only one record fails. Which feature should be enabled?

Accepted Answer

Partial batch response for SQS event source mapping. Partial batch response for SQS event source mapping allows the Lambda function to report which messages in a batch failed processing. When enabled, Lambda retries only the failed messages instead of the entire batch, preventing successful messages from being reprocessed or lost. This is achieved by returning a `batchItemFailures` array in the function's response, which tells Lambda which message IDs to retry.

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Reserved concurrency of one

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Maximum message size increase

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SQS short polling

Question 15

A service needs loosely coupled asynchronous communication where one producer sends events to many different AWS service targets using rules. Which service fits best?

Accepted Answer

Amazon EventBridge. Amazon EventBridge is a serverless event bus service that enables loosely coupled asynchronous communication. It allows a single producer to publish events, and then uses rules to route those events to multiple AWS service targets (e.g., Lambda, SQS, Step Functions) simultaneously, fulfilling the requirement exactly.

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Amazon EFS

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AWS CloudHSM

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AWS DataSync