DVA-C02 Development with AWS Services Practice Test 18 — 15 Questions

Question 1

A developer is building a RESTful API using Amazon API Gateway (REST API) and AWS Lambda. The API receives a large number of requests with duplicate payloads within a short time window. To improve performance and reduce costs, the developer wants to ensure that if the same request (based on a unique client ID) is sent within 5 minutes, the Lambda function is not invoked again, and the previously calculated response is returned. Which API Gateway feature should the developer use?

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

Accepted Answer

Enable API caching on the stage with a TTL of 300 seconds and configure the client ID as a cache key parameter.. Amazon API Gateway (REST API) supports response caching at the stage level. By enabling API caching with a TTL of 300 seconds (5 minutes) and specifying the client ID as a cache key parameter, identical requests with the same client ID within the TTL will return the cached response without invoking the Lambda function. This reduces latency and cost.

Answer

Enable request validation to reject duplicate requests.

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Configure a usage plan with a throttle rate to limit requests from each client.

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Enable stage variables to store the previous response.

Question 2

A developer is building a RESTful API using Amazon API Gateway (REST API) and AWS Lambda. The API receives a large number of requests with duplicate payloads within a short time window. To improve performance and reduce costs, the developer wants to ensure that if the same request (based on a unique client ID) is sent within 5 minutes, the Lambda function is not invoked again, and the previously calculated response is returned. Which API Gateway feature should the developer use?

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

Accepted Answer

The custom domain name's DNS record does not point to API Gateway's regional domain name.. The most likely cause is that the custom domain name's DNS record does not point to API Gateway's regional domain name. When using a custom domain name with API Gateway, you must create a DNS record (typically a CNAME or A record using Route 53 alias) that maps your custom domain to the API Gateway-generated regional domain name (e.g., d-xxxxx.execute-api.region.amazonaws.com). Without this correct DNS mapping, the SSL/TLS handshake fails because the certificate presented by API Gateway does not match the domain name the client is connecting to, resulting in an SSL error.

Answer

The certificate was not issued by a trusted certificate authority.

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The API Gateway API is not deployed to a stage that is mapped to the custom domain name.

Answer

The certificate is in the wrong region relative to the API Gateway regional endpoint.

Question 3

A developer is building a system that reads messages from an Amazon SQS queue, processes them, and stores results in an Amazon DynamoDB table. The developer wants to use a managed service to coordinate the processing steps, including error handling and retry logic, without provisioning any servers. Which AWS service should the developer use?

Accepted Answer

AWS Step Functions. AWS Step Functions is a serverless orchestration service that lets you coordinate multiple AWS services into a workflow. It directly supports error handling, retry logic, and conditional branching, making it ideal for managing the processing steps of messages from SQS through to DynamoDB without provisioning any servers.

Answer

Amazon Simple Workflow Service (SWF)

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AWS Glue

Answer

Amazon MQ

Question 4

A developer is building a serverless application using AWS Lambda and Amazon API Gateway. The API must support different HTTP methods (GET, POST, PUT, DELETE) for the same resource path. The developer wants to define the API in a single Lambda function that can handle all methods without additional mapping configuration. Which Lambda integration type should the developer use?

Accepted Answer

Lambda proxy integration. Lambda proxy integration (option A) is correct because it allows a single Lambda function to handle all HTTP methods (GET, POST, PUT, DELETE) for the same resource path without additional mapping configuration. In this integration type, API Gateway passes the entire client request (method, headers, query parameters, body) as a JSON event to the Lambda function, and the function must return a response in a specific format that includes status code, headers, and body. This eliminates the need for manual mapping templates or method-specific configurations.

Answer

Lambda custom integration

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AWS service integration

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HTTP integration

Question 5

A developer is building a serverless application that processes user-submitted images. The images are uploaded to an S3 bucket, which triggers an AWS Lambda function that creates a thumbnail and stores it in another S3 bucket. The developer notices that sometimes the Lambda function is invoked multiple times for a single image upload. What should the developer configure to ensure idempotent processing?

Accepted Answer

Implement a DynamoDB table to track processed objects.. S3 event notifications can occasionally deliver duplicate events (at-least-once semantics). By storing the unique object key (or ETag) in a DynamoDB table with a TTL, the Lambda function can check if the object has already been processed and skip duplicate invocations, ensuring idempotent processing.

Answer

Enable S3 event notifications with a suffix filter.

Answer

Use an SQS queue to decouple S3 events.

Answer

Increase the Lambda function's timeout.

Question 6

A developer is building a multi-region application using Amazon DynamoDB global tables. The application needs to read data from a replica table in a different region shortly after a write in the primary region. The developer notices that reads sometimes return stale data. Which of the following explains this behavior?

Accepted Answer

Global tables use asynchronous replication, introducing unavoidable replication lag.. Amazon DynamoDB global tables use asynchronous replication to propagate writes from one region to all other replica tables. This means that after a write in the primary region, there is an inherent replication lag (typically sub-second but can be higher under load or network issues) before the change is visible in other regions. The developer observes stale reads because the read is hitting a replica that has not yet received the update, which is expected behavior for eventually consistent reads on global tables.

Answer

The developer must use DynamoDB Streams to capture changes and replicate them separately.

Answer

The developer must enable strong consistency reads on the replica table.

Answer

The global table must be configured with write forwarding.

Question 7

A developer is migrating a monolithic application to a microservices architecture on AWS. The application uses a relational database. The developer wants to use Amazon RDS for the database and needs to ensure that each microservice can only access its own set of tables. Which approach should the developer take?

Accepted Answer

Use RDS with IAM database authentication and create database users with limited privileges for each microservice.. IAM database authentication allows the developer to create database users with granular, table-level privileges using standard SQL GRANT statements, ensuring each microservice can only access its own set of tables. By combining IAM roles with database user credentials, the developer can enforce least-privilege access without sharing a single database user across services. This approach directly addresses the requirement for per-microservice table isolation while leveraging RDS's native authentication and authorization capabilities.

Answer

Create a single RDS instance with a separate database per microservice.

Answer

Use RDS in a VPC and restrict network access per microservice using security groups.

Answer

Use Amazon RDS Proxy to control access.

Question 8

A developer is running a web application on multiple Amazon EC2 instances behind an Application Load Balancer (ALB). The application needs to store user session state that must be available across all instances. The session data is small and temporary but must survive individual instance failures. Which AWS service should the developer use to store this session state?

Accepted Answer

Store session state in an Amazon ElastiCache cluster. Amazon ElastiCache (e.g., using Redis or Memcached) provides a centralized, in-memory data store that is external to the EC2 instances. This allows all instances behind the ALB to read and write the same session state, ensuring consistency across the fleet. Because the data is stored in a managed cluster, it survives individual instance failures and is ideal for small, temporary session data that requires low-latency access.

Answer

Store session state in the /tmp directory of each EC2 instance

Answer

Use an Amazon SQS queue to persist session data

Answer

Store session state in an Amazon S3 bucket

Question 9

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.. 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 10

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.. 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 11

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 12

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 13

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. 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 14

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

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AWS CloudFront

Answer

Amazon S3

Question 15

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. 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