DVA-C02 Development with AWS Services Practice Test 2 — 15 Questions

Question 1

A developer is building a web application that uses Amazon DynamoDB as the database. The application needs to store user session data and must support eventual consistency reads for most use cases, but strongly consistent reads for critical operations. The developer wants to minimize costs. Which read capacity unit (RCU) configuration should the developer use?

Accepted Answer

Use on-demand capacity mode to pay per request, avoiding provisioned capacity costs.. Option A is correct because on-demand capacity mode charges per request (read/write), eliminating the need to provision fixed RCUs. For a session store with mixed consistency requirements, on-demand is cost-effective when traffic is unpredictable or low, as you only pay for actual reads and writes. Eventually consistent reads consume half the RCUs of strongly consistent reads, but on-demand pricing automatically accounts for this difference without manual configuration.

Answer

Use provisioned capacity with 1 RCU per item, since eventually consistent reads consume half the RCUs.

Answer

Use provisioned capacity with sufficient RCUs to handle strongly consistent reads, as they consume the same as eventually consistent.

Answer

Use provisioned capacity with enough RCUs for peak traffic, and use DynamoDB Accelerator (DAX) for caching.

Question 2

A developer is building a serverless application using AWS SAM. The application includes an Amazon API Gateway endpoint with a Lambda function that processes user uploads. The developer wants to enable API caching in the development stage to speed up repeated requests, but disable caching in the production stage. What is the most efficient way to achieve this?

Accepted Answer

Configure caching in the SAM template using the CacheClusterEnabled property and use CloudFormation conditions to enable it only in the dev stage.. Option A is correct because AWS SAM extends AWS CloudFormation, allowing you to use CloudFormation conditions to conditionally enable the `CacheClusterEnabled` property on the `AWS::ApiGateway::Stage` resource. By defining a condition that evaluates to true only for the dev stage (e.g., based on a parameter like `StageName`), you can enable caching in dev and disable it in prod within a single SAM template, avoiding duplication and manual steps.

Answer

Create two separate SAM templates, one for dev with caching and one for prod without.

Answer

Enable caching in the API Gateway console after each deployment for the dev stage.

Answer

Use a custom CloudFormation resource to toggle caching based on a parameter.

Question 3

A developer is building a serverless application using AWS Lambda and Amazon DynamoDB. The application needs to store large JSON documents (up to 1 MB) and retrieve them by a primary key. The documents are updated frequently. Which DynamoDB feature should the developer consider to optimize performance and cost for storing and retrieving these large items?

Accepted Answer

Use Amazon S3 to store the documents and store only the S3 key in DynamoDB.. Option A is correct because DynamoDB has a 400 KB item size limit, so storing large JSON documents (up to 1 MB) directly in DynamoDB is not possible. By storing the documents in Amazon S3 (which supports objects up to 5 TB) and keeping only the S3 object key in DynamoDB, the developer can efficiently retrieve the document via the primary key while avoiding DynamoDB's size constraint. This pattern also reduces DynamoDB read/write capacity unit consumption, lowering cost for frequently updated large items.

Answer

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

Answer

Use DynamoDB Transactions to atomically update the items.

Answer

Enable DynamoDB Streams to capture changes to the items.

Question 4

A developer is building a serverless application using AWS Step Functions. The workflow must execute hundreds of thousands of short-lived tasks per day, each taking less than 30 seconds. The tasks need to run in parallel, and a small number of duplicate executions are acceptable. Which type of Step Functions workflow should the developer choose?

Accepted Answer

Express Workflow. Express Workflows are designed for high-volume, short-duration (under 5 minutes) event-processing workloads, executing hundreds of thousands of state transitions per second with at-least-once semantics. Since the tasks are short-lived (under 30 seconds), run in parallel, and tolerate a small number of duplicate executions, Express Workflow is the correct choice because it offers lower cost and higher throughput than Standard Workflow, which guarantees exactly-once execution and is better suited for long-running, auditable workflows.

Answer

Standard Workflow

Answer

AWS Lambda function with synchronous invocation

Answer

Amazon Simple Workflow Service (SWF)

Question 5

A developer is using the AWS Serverless Application Model (SAM) to define a serverless application with an API Gateway endpoint. The developer wants to enable API caching only in the development stage to speed up testing, but disable it in the production stage to ensure data freshness. What is the most efficient way to achieve this with SAM?

Accepted Answer

Use AWS SAM parameters with a condition to set CacheClusterEnabled based on the stage parameter.. AWS SAM parameters allow you to define a stage parameter (e.g., 'dev' or 'prod') and use a condition to conditionally set the `CacheClusterEnabled` property on the `AWS::Serverless::Api` resource. This is the most efficient approach because it uses a single template and SAM's built-in intrinsic functions (like `Fn::Equals`) to toggle caching based on the deployment stage, avoiding separate templates or post-deployment custom resources.

Answer

Deploy two separate SAM templates, one for each stage.

Answer

Use a custom resource to toggle caching after deployment.

Answer

Enable caching globally and configure a usage plan with a quota for production.

Question 6

A developer is building a serverless application using AWS SAM that includes an API Gateway REST API and a Lambda function. The developer wants to pass environment variables to the Lambda function based on the deployment stage (dev/prod). The stage name is provided as a SAM parameter. How should the developer define this in the SAM template?

Accepted Answer

Define a SAM Parameter for the stage name, and reference it in the Lambda function's Environment property. Option A is correct because AWS SAM allows you to define parameters (e.g., StageName) and reference them directly in the Lambda function's Environment property using CloudFormation intrinsic functions like !Ref. This enables dynamic injection of environment variables based on the deployment stage without modifying the template structure, aligning with Infrastructure as Code best practices for multi-environment deployments.

Answer

Use the Globals section of the SAM template to set environment variables

Answer

Hard-code the environment variables with different values in the template

Answer

Use an AWS Systems Manager Parameter Store parameter and reference it in the function

Question 7

A developer is building a RESTful API that allows clients to query a database and retrieve results. The backend logic is implemented in AWS Lambda, which queries an Amazon DynamoDB table. The developer wants to expose the API over HTTPS and manage authentication and throttling. Which AWS service should the developer use to create and manage the API endpoints?

Accepted Answer

Amazon API Gateway. Amazon API Gateway is the correct choice because it is a fully managed service that enables developers to create, publish, maintain, monitor, and secure RESTful APIs at any scale. It directly supports HTTPS endpoints, integrates natively with AWS Lambda for backend logic, and provides built-in features for authentication (e.g., IAM, Cognito, Lambda authorizers) and throttling (usage plans and rate limits). This makes it the ideal service for exposing a Lambda-backed DynamoDB query as a secure, managed API.

Answer

Application Load Balancer

Answer

AWS CloudFront

Answer

Amazon S3

Question 8

A developer is building a serverless application that uses Amazon S3 event notifications to trigger an AWS Lambda function for thumbnail generation. The developer wants to ensure that duplicate S3 events do not cause the same image to be processed multiple times. Which approach should the developer implement to ensure idempotent processing?

Accepted Answer

Store the object key and event ID in a DynamoDB table and check for duplicates before processing. Option A is correct because storing the S3 object key and event ID in a DynamoDB table with a TTL attribute allows the Lambda function to perform a conditional write (or check for an existing item) before processing. This ensures that even if duplicate S3 events are delivered (e.g., due to S3's at-least-once delivery guarantee), the same image is only processed once, achieving idempotency.

Answer

Set the Lambda function's concurrency to 1 to prevent concurrent executions

Answer

Use an Amazon SQS FIFO queue as the event destination

Answer

Enable S3 event notification filtering based on object size

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. 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

Add a suffix filter to the S3 event notification that includes .jpg and .png.. Option B is correct because S3 event notifications support suffix filters that allow you to specify which object key suffixes (e.g., .jpg and .png) trigger the event. By adding a suffix filter for .jpg and .png, only image file uploads invoke the Lambda function, directly reducing unnecessary invocations and costs without requiring any code changes in the function.

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.

Answer

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 10

A developer is building a serverless application that needs to store user session data. The data is small (a few KB per user) and must be accessible across multiple invocations of the same Lambda function and across different Lambda functions. The session data should persist for the duration of the user session (up to 1 hour). Which storage solution should the developer use?

Accepted Answer

Amazon ElastiCache with Redis. Amazon ElastiCache with Redis is the correct choice because it provides an in-memory data store with sub-millisecond latency, making it ideal for storing small, ephemeral session data that needs to be shared across multiple Lambda invocations and functions. Redis supports key-value storage with configurable Time-to-Live (TTL) for automatic expiration, aligning perfectly with the 1-hour session duration requirement. Unlike other options, ElastiCache is designed for low-latency, cross-function access without the overhead of database writes or file system limitations.

Answer

Amazon DynamoDB with TTL

Answer

Amazon S3

Answer

Local storage (Lambda ephemeral storage /tmp)

Question 11

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

Change the visibility timeout using the UpdateStack API; messages will be unaffected as long as the new timeout is longer than the current one.. Option C is correct because the UpdateStack API allows you to modify the visibility timeout of an SQS queue without disrupting in-flight messages, as long as the new timeout is longer than the current one. This ensures that messages already being processed have sufficient time to complete before becoming visible again, preventing any message loss. CloudFormation handles the update by applying the change to the queue resource definition and triggering a stack update that modifies the queue's configuration without deleting or recreating it.

Answer

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

Answer

Update the stack directly; CloudFormation will automatically handle in-flight messages.

Answer

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

Question 12

A developer is implementing an e-commerce application where a purchase operation must deduct inventory and create an order atomically. The inventory and orders are stored in separate DynamoDB tables. Which DynamoDB feature should the developer use to execute these operations as a single, all-or-nothing transaction?

Accepted Answer

DynamoDB Transactions. DynamoDB Transactions provide ACID (Atomicity, Consistency, Isolation, Durability) guarantees across one or more tables within a single AWS account and region. This allows the developer to combine the deduct-inventory and create-order operations into a single all-or-nothing transaction, ensuring that both succeed or both fail without partial updates.

Answer

DynamoDB Streams

Answer

DynamoDB Accelerator (DAX)

Answer

DynamoDB Global Tables

Question 13

A developer is building a serverless application using AWS Lambda and Amazon API Gateway. The API requires that the same Lambda function handle different HTTP methods (GET, POST, DELETE) for the same resource. The developer wants to minimize code and configuration. Which integration type should the developer use?

Accepted Answer

Lambda proxy integration. Lambda proxy integration (option A) is correct because it automatically passes the entire HTTP request (method, headers, query parameters, path parameters) to the Lambda function as a single event object, allowing the same function to inspect the `httpMethod` field and branch logic for GET, POST, DELETE without any additional API Gateway mapping or transformation configuration. This minimizes both code (the function handles routing internally) and configuration (no need to define separate integration requests/responses per method).

Answer

Lambda custom integration

Answer

HTTP integration

Answer

Mock integration

Question 14

An application running on Amazon EC2 instances behind an Application Load Balancer (ALB) intermittently returns 503 errors. The ALB health checks are failing for some instances intermittently. The developer checks the instance system logs and finds no application errors. What is the most likely cause of the health check failures?

Accepted Answer

The application on the instances is experiencing resource exhaustion (e.g., memory or CPU) which causes it to stop responding to health checks temporarily. Intermittent 503 errors from the ALB combined with intermittent health check failures and no application errors in the system logs strongly point to transient resource exhaustion (CPU or memory) on the EC2 instances. When an instance runs out of memory or CPU, the application process may become unresponsive or be killed by the OS (e.g., OOM killer), causing it to fail health checks temporarily. Once resources are freed (e.g., after a spike subsides), the application resumes responding, which explains the intermittent nature of the failures.

Answer

The security group for the instances does not allow inbound traffic from the ALB on the health check port

Answer

The health check path is not configured correctly and the default path returns a 404 status

Answer

The target group is not configured with the correct protocol

Question 15

A company is building a RESTful API using Amazon API Gateway and AWS Lambda. The API must allow users to authenticate using an identity provider that supports OpenID Connect (OIDC). The developer wants to offload authentication and authorization to API Gateway. Which API Gateway feature should the developer use?

Accepted Answer

Native JWT authorizer (HTTP API). Option C is correct because the Native JWT authorizer for HTTP APIs in API Gateway directly validates JSON Web Tokens (JWTs) from an OIDC-compliant identity provider without requiring custom code. This offloads both authentication and authorization to API Gateway by configuring the issuer URL and audience, matching the requirement to use an OIDC provider.

Answer

Amazon Cognito User Pools authorizer

Answer

Custom Lambda authorizer

Answer

AWS IAM authorizer