DVA-C02 Development with AWS Services — 20 Questions

Question 1

A developer is building a serverless application that processes orders. An order is placed and an event is published to an Amazon SNS topic. The SNS topic has multiple subscribers, including an SQS queue for order processing and a Lambda function for sending notifications. The developer wants to ensure that the SQS queue receives all messages reliably, even if the processing Lambda function fails temporarily. Which configuration should the developer set?

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

Accepted Answer

Enable a dead-letter queue on the SQS queue. When an Amazon Lambda function is configured to process messages from an Amazon SQS queue (via an event source mapping), any failed messages are returned to the queue. To prevent poison-pill messages from repeatedly failing and blocking the queue, a Dead-Letter Queue (DLQ) must be configured on the source SQS queue itself (using a redrive policy). Configuring a DLQ on the Lambda function itself only works for asynchronous invocations, not for SQS event source mappings (which use synchronous polling under the hood).

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Enable SNS delivery retries for HTTP endpoints

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Set the SQS queue's visibility timeout to a value greater than the Lambda function's processing time

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Configure the SNS topic to use server-side encryption

Question 2

A developer is building a serverless application that processes orders. An order is placed and an event is published to an Amazon SNS topic. The SNS topic has multiple subscribers, including an SQS queue for order processing and a Lambda function for sending notifications. The developer wants to ensure that the SQS queue receives all messages reliably, even if the processing Lambda function fails temporarily. Which configuration should the developer set?

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

Accepted Answer

The Lambda function is not deleting messages from the queue after successful processing, so they become visible again after the visibility timeout.. When using an Amazon SQS queue as an event source for AWS Lambda, the Lambda service automatically deletes messages from the queue after your function successfully processes them. However, if the SQS queue's visibility timeout is shorter than the Lambda function's timeout, a message might become visible again in the queue while the Lambda function is still processing it. This allows another Lambda instance to retrieve and process the same message, resulting in duplicate processing.

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The Lambda function is configured with a batch size greater than 1, causing multiple messages to be processed at once and some to be duplicated.

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The SQS queue has a message retention period set too low, causing messages to be deleted automatically and re-queued.

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The Lambda function's execution role does not have permission to delete messages from the queue.

Question 3

A developer is building a serverless application that processes orders. An order is placed and an event is published to an Amazon SNS topic. The SNS topic has multiple subscribers, including an SQS queue for order processing and a Lambda function for sending notifications. The developer wants to ensure that the SQS queue receives all messages reliably, even if the processing Lambda function fails temporarily. Which configuration should the developer set?

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

Accepted Answer

Use Amazon S3 to store the documents and store only the S3 key in DynamoDB.. DynamoDB has a strict 400 KB item size limit, making it impossible to store 1 MB documents directly. The standard design pattern is to store the large payload in Amazon S3 and save the S3 object reference (URI/key) in the DynamoDB item. Changing the question stem to ask for the 'approach' or 'design pattern' instead of 'DynamoDB feature' resolves this contradiction.

Answer

Enable DynamoDB Accelerator (DAX) to cache the large items.

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Use DynamoDB Transactions to atomically update the items.

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Enable DynamoDB Streams to capture changes to the items.

Question 4

A developer configures an AWS Lambda function to process image files uploaded to an S3 bucket. The bucket receives a mix of .jpg, .png, and .pdf files. To reduce costs, the developer wants the Lambda function to be invoked only for image files (.jpg and .png). How should the developer configure the S3 event notification?

Accepted Answer

Configure the S3 event notification to invoke the Lambda function for all object create events, and add logic in the Lambda function to exit early if the object is not an image.. Amazon S3 Event Notifications have a strict limitation: they do not support multiple suffixes in a single filter, and they do not allow overlapping rules (e.g., two rules with the same prefix/empty prefix but different suffixes like .jpg and .png). To achieve suffix filtering for multiple extensions (.jpg and .png) without invoking Lambda for other files (like .pdf), you must enable EventBridge notifications on the S3 bucket and create an EventBridge rule with an event pattern that filters by suffix. This avoids unnecessary Lambda invocations and reduces costs.

Answer

Add a suffix filter to the S3 event notification that includes .jpg and .png.

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Set the S3 bucket policy to deny PutObject requests that do not have a .jpg or .png suffix.

Answer

Create two separate S3 buckets: one for images and one for other files, and configure the event notification only on the image bucket.

Question 5

A developer is building a serverless application that processes orders. An order is placed and an event is published to an Amazon SNS topic. The SNS topic has multiple subscribers, including an SQS queue for order processing and a Lambda function for sending notifications. The developer wants to ensure that the SQS queue receives all messages reliably, even if the processing Lambda function fails temporarily. Which configuration should the developer set?

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

Accepted Answer

Amazon DynamoDB with TTL. Amazon DynamoDB is a fully serverless, managed NoSQL database that integrates seamlessly with AWS Lambda without requiring a VPC. It offers single-digit millisecond latency, which is more than sufficient for user session data. By enabling Time to Live (TTL), DynamoDB can automatically delete expired session items after 1 hour at no extra cost, making it the ideal and most cost-effective storage solution for serverless session state.

Answer

Amazon ElastiCache with Redis

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Amazon S3

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Local storage (Lambda ephemeral storage /tmp)

Question 6

A developer wants to update an AWS CloudFormation stack that includes an Amazon SQS queue. The queue is currently processing messages. The developer needs to change the queue's default visibility timeout without losing any messages. Which approach should the developer take?

Accepted Answer

Update the stack directly; CloudFormation will automatically handle in-flight messages.. Updating the VisibilityTimeout property of an AWS::SQS::Queue resource in CloudFormation does not cause resource replacement (it requires 'No interruption'). Therefore, you can update the stack directly with the new visibility timeout. CloudFormation will apply the change in-place, and existing messages in the queue (including those in-flight) will not be lost or affected. SQS does not require the new timeout to be longer than the old one to preserve messages.

Answer

Delete the stack and recreate it with the updated visibility timeout.

Answer

Change the visibility timeout using the UpdateStack API; messages will be unaffected as long as the new timeout is longer than the current one.

Answer

Stop the queue, update the visibility timeout, then resume the queue.

Question 7

An independent software vendor (ISV) is building a serverless application that processes incoming HTTP requests. The incoming requests must be validated against an OpenAPI schema before being passed to the Lambda function. Which AWS service should the ISV use to perform this validation?

Accepted Answer

Amazon API Gateway (with request validation). Amazon API Gateway's request validation feature can validate incoming HTTP requests against an OpenAPI (Swagger) schema before the request reaches the Lambda function. This offloads validation from the Lambda code, reducing cost and latency by rejecting invalid requests early. The ISV can define the schema in the API Gateway REST API, and API Gateway will automatically check headers, query strings, and request bodies against the schema. Note that this feature is supported by API Gateway REST APIs, but not by HTTP APIs.

Answer

AWS WAF

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Amazon Cognito

Answer

AWS AppSync

Question 8

A developer is building an application that needs to store session state data for a web application running on multiple EC2 instances behind an ALB. The data is ephemeral and should not persist if an instance is terminated. Which storage option should the developer use?

Accepted Answer

Amazon ElastiCache. Amazon ElastiCache is the correct choice because it provides an in-memory, low-latency data store (Redis or Memcached) ideal for session state. By storing session state in ElastiCache, the data is shared across all EC2 instances behind the ALB and survives the termination of any individual EC2 instance, preventing user session loss while avoiding the overhead of a traditional relational database.

Answer

Amazon RDS

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Amazon DynamoDB

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Amazon S3

Question 9

A developer configures an AWS Lambda function to process image files uploaded to an S3 bucket. The bucket receives a mix of .jpg, .png, and .pdf files. The developer wants to invoke the Lambda function only for image files to reduce costs. Which configuration should the developer use?

Accepted Answer

Configure an S3 event notification with a suffix filter '.jpg' and '.png'. S3 event notifications support suffix filtering. By configuring S3 event notifications with suffix filters for '.jpg' and '.png' pointing to the Lambda function, the developer ensures the function is only invoked for those file types, avoiding unnecessary invocations for .pdf files and reducing costs.

Answer

Configure an S3 event notification with a prefix filter 'images/'

Answer

Create a Lambda resource-based policy that denies invocation from S3 for .pdf objects

Answer

Add an S3 bucket policy that denies PutObject for any object that is not a .jpg or .png

Question 10

A developer is building a serverless application using AWS Lambda and Amazon DynamoDB. The application needs to store and retrieve session data. The session data has a TTL of 30 minutes. Which DynamoDB feature should the developer use to automatically delete expired items?

Accepted Answer

Use DynamoDB Time to Live (TTL) to set an expiry time attribute that DynamoDB automatically deletes when the TTL is reached.. DynamoDB Time to Live (TTL) is the correct feature because it allows you to define a per-item timestamp attribute. When that timestamp is reached, DynamoDB automatically deletes the item without any additional cost or custom code. This directly meets the requirement to automatically delete expired session data after 30 minutes.

Answer

Use DynamoDB Streams to capture expired items and trigger a Lambda function for deletion.

Answer

Use DynamoDB Global Tables to replicate data to another region and then set a TTL on the replica.

Answer

Use DynamoDB Accelerator (DAX) to cache the data and expire it based on a cache TTL.

Question 11

A developer is storing application configuration data in DynamoDB. The data is frequently accessed by partition key, and items are small (less than 1KB). The read traffic is consistent and predictable. Which read capacity mode is most cost-effective for this workload?

Accepted Answer

Provisioned with reserved capacity. For a consistent and predictable workload, Provisioned Capacity is more cost-effective than On-demand. To achieve the maximum cost savings (most cost-effective), purchasing DynamoDB Reserved Capacity (Option C) is the best choice. Reserved capacity allows you to pay a one-time upfront fee and commit to a minimum usage level for a 1-year or 3-year term, yielding significant discounts compared to standard provisioned capacity rates.

Answer

On-demand

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Provisioned with auto scaling

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Provisioned with fixed capacity

Question 12

A developer is building a RESTful API using AWS Lambda and Amazon API Gateway. The API needs to support HTTP methods GET, POST, and DELETE. The developer wants to minimize code and operational overhead. Which API Gateway integration type should the developer use?

Accepted Answer

Lambda proxy integration. Lambda proxy integration is the simplest and most common approach. It passes the entire request to the Lambda function, which handles routing and response formatting, minimizing code and overhead. Custom integration requires mapping templates, HTTP integration forwards to an HTTP endpoint, and mock integration is for testing.

Answer

Lambda custom integration

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HTTP integration

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Mock integration

Question 13

A developer wants to store session state data for a web application running on multiple EC2 instances behind an Application Load Balancer. The data is ephemeral and should not persist if an instance is terminated. Which storage option should the developer use?

Accepted Answer

Amazon ElastiCache. Amazon ElastiCache is the correct choice because it provides an in-memory, high-performance, shared data store (using Redis or Memcached) that is ideal for storing session state. Because ElastiCache is external to the EC2 instances, session data is preserved even if individual EC2 instances are terminated or scaled in/out by an Auto Scaling group. This allows other EC2 instances behind the Application Load Balancer to seamlessly retrieve the user's session state.

Answer

Amazon RDS

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Amazon S3

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Amazon EFS

Question 14

A Kinesis consumer Lambda shows increasing IteratorAge. Which two changes may improve throughput when processing is CPU-bound?

Accepted Answer

Increase Lambda memory to provide more CPU. Increasing Lambda memory proportionally increases CPU allocation, which directly improves throughput for CPU-bound processing by reducing per-record processing time. Additionally, increasing the stream shard count increases the number of concurrent Lambda executions (since Lambda scales with the number of shards by default), allowing more batches to be processed in parallel. Both changes help reduce IteratorAge by increasing overall processing throughput.

Answer

Reduce the number of stream shards

Answer

Disable checkpointing

Question 15

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.

Answer

Standard queue delay seconds

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Dead-letter queue redrive policy

Answer

Visibility timeout extension

Question 16

A Lambda function writes order records to DynamoDB after receiving API Gateway requests. Which two practices improve reliability during client retries?

Accepted Answer

Use an idempotency token from the request in a conditional DynamoDB write. Using an idempotency token from the request in a conditional DynamoDB write (Option A) ensures that if a client retries the same request, the Lambda function can check whether the token already exists in the table. If it does, the write is skipped, preventing duplicate order records. Returning the same result for repeated requests with the same idempotency key (Option C) ensures that the client receives a consistent response (e.g., the original success response) without causing duplicate side effects, which is a core requirement of idempotent API design.

Answer

Generate a new random primary key for every retry

Answer

Disable API Gateway request validation

Question 17

An event-driven application uses EventBridge rules to route partner events. Which two design choices improve maintainability?

Accepted Answer

Use event patterns that match stable business attributes. Using event patterns that match stable business attributes (Option A) decouples routing logic from infrastructure details, ensuring rules remain valid even if underlying service endpoints change. Using a custom event bus or partner event source separation (Option D) ensures that partner events are isolated from internal traffic, which simplifies access control, auditing, and rule management, thereby improving maintainability. Option B creates a monolithic Lambda function that is hard to maintain. Option C is a severe security risk. A fifth option should be added to make this a standard 5-option multiple-response question (e.g., 'E: Route all events to a single default event bus without separation').

Answer

Put all routing logic in a single Lambda that invokes every target

Answer

Hardcode account root credentials in targets

Question 18

Match each AWS service to its category.

Accepted Answer

EC2: Compute. AWS services are categorized by main function: compute (EC2), storage (S3), database (RDS), and messaging (SQS). Messaging services like SQS are crucial for decoupling applications, while each service type serves a distinct purpose.

Answer

EC2: Database

Answer

S3: Messaging

Question 19

A developer needs to store session state for a stateless web application running on EC2 instances behind an Application Load Balancer. Which AWS service should the developer use to ensure session data is not lost if an instance fails?

Accepted Answer

Amazon DynamoDB. Amazon DynamoDB is a fully managed NoSQL database that provides fast and predictable performance with seamless scalability. It is highly recommended for storing session state in stateless applications because it is serverless, highly durable, and requires no cluster management, unlike ElastiCache. AWS SDKs even offer native session state providers for DynamoDB.

Answer

Amazon S3

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Amazon ElastiCache

Answer

Amazon RDS

Question 20

A developer is designing a serverless application using AWS Lambda, Amazon API Gateway, and Amazon DynamoDB. The application experiences occasional throttling on the Lambda function during peak traffic. The developer needs to reduce the number of throttling errors without changing the Lambda function code. Which solution should the developer implement?

Accepted Answer

Enable API Gateway caching.. Enabling API Gateway caching reduces the number of requests that reach the Lambda function by serving cached responses for identical requests. This directly decreases the number of Lambda invocations during peak traffic, thereby reducing or eliminating Lambda throttling errors without requiring any changes to the Lambda function code.

Answer

Increase the Lambda function timeout.

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Increase the DynamoDB read capacity units.

Answer

Configure reserved concurrency on the Lambda function.