AWS Developer Associate - DVA-C02

About the DVA-C02 certification

Exam code

DVA-C02

Official exam guideDomain weightings come from the vendor and change over time. Check the official guide before you book.

1. 1.A developer is building an order service that must notify three downstream services when an order is placed. Each downstream service processes at its own rate, and none of them may lose an event if it is temporarily offline. The producer must not know which consumers exist. Which design meets these requirements?

   • APublish to an Amazon SNS topic with one Amazon SQS queue subscribed per downstream service.Correct answer
   • BPublish to an Amazon SNS topic with each downstream service subscribed as an HTTPS endpoint.
   • CPublish to a single Amazon SQS queue that all three downstream services poll.
   • DCall each downstream service synchronously over HTTP and retry on failure.

   Why

   The fanout pattern publishes the event once to an Amazon SNS topic and subscribes one Amazon SQS queue per consumer. The producer stays unaware of the consumers, each consumer drains its own queue at its own pace, and messages persist while a consumer is down. Subscribing the services directly to SNS loses events for any endpoint that is offline. A single shared queue delivers each message to only one consumer. Direct HTTP calls couple the producer to every consumer.

2. 2.An application calls a third-party payment API that occasionally returns HTTP 503 responses and sometimes stops responding entirely for several minutes. During those outages the application exhausts its thread pool and becomes unresponsive. Which combination of patterns should the developer implement? (Select TWO.)

   • ARetry failed calls using exponential backoff with jitter.Correct answer
   • BWrap the dependency in a circuit breaker that stops calls after a failure threshold.Correct answer
   • CRetry failed calls immediately in a loop until they succeed.
   • DRemove the client-side timeout so slow responses are never cut off.
   • ECache the failed responses and return them to callers during the outage.

   Why

   Exponential backoff with jitter spaces out retries and prevents a synchronized retry storm from every client at once. A circuit breaker stops sending calls once a failure threshold is reached, so threads are no longer consumed waiting on a dependency that is known to be failing, and it probes periodically before closing again. Retrying immediately in a tight loop makes the outage worse. Removing the timeout is what allows threads to pile up. Caching failed responses would serve incorrect data.

3. 3.A developer must route events from an application to different targets based on the content of the event body, for example sending events where detail.status equals CANCELLED to one AWS Lambda function and all others to another. The routing rules must be managed without changing application code. Which service should the developer use?

   • AAmazon EventBridge with event pattern rules on the event detail fields.Correct answer
   • BAmazon SQS with one queue per event type and a router consumer.
   • CAWS Step Functions with a Choice state for each event type.
   • DAmazon Kinesis Data Streams with one shard per event type.

   Why

   Amazon EventBridge evaluates event pattern rules against the JSON structure of each event and routes matches to the configured targets, so routing logic lives in rules rather than in application code. Amazon SQS has no content-based routing. Amazon SNS supports subscription filter policies on message attributes but is a simpler pub/sub primitive without EventBridge rule targets and buses. AWS Step Functions orchestrates workflow state rather than routing arbitrary published events.

4. 4.An Amazon SQS consumer occasionally processes the same message twice, which creates duplicate database records. The team cannot switch to a FIFO queue because of throughput requirements. What should the developer implement to prevent duplicate side effects?

   • AMake the consumer idempotent by recording a deterministic message key in Amazon DynamoDB with a conditional write.Correct answer
   • BIncrease the visibility timeout so the message is not delivered again.
   • CDelete the message from the queue as soon as it is received, before processing it.
   • DEnable long polling on the queue to avoid receiving the same message twice.

   Why

   Standard queues guarantee at-least-once delivery, so consumers must be idempotent. Deriving a deterministic idempotency key from the message and recording processed keys in a store such as Amazon DynamoDB with a conditional write makes a repeated delivery a no-op. Increasing the visibility timeout reduces but never eliminates duplicate delivery. Deleting the message before processing loses messages when processing fails. Long polling only affects how receives are polled.

5. 5.A REST API built with Amazon API Gateway must reject requests whose JSON body is missing required fields, before the request reaches the backend AWS Lambda function. The team wants to avoid writing validation code in the function. What should the developer configure?

   • AAttach a model with a JSON Schema to the method and enable request body validation.Correct answer
   • BAdd validation logic at the start of the Lambda function and return a 400 response.
   • CCreate a usage plan with a request quota for the API stage.
   • DConfigure a Lambda authorizer that inspects the request body.

   Why

   API Gateway request validators check the request body against a JSON Schema model, along with required query string parameters and headers, and return a 400 response without invoking the backend integration. Validating inside the Lambda function still pays for the invocation. A usage plan controls throttling and quotas. A Lambda authorizer handles authentication and authorization, not payload shape.

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