AWS DVA-C02 Drill: Asynchronous Lambda Invocation - Parallel Integration Without Failure Dependency

Jeff’s Note

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Unlike generic exam dumps, ADH analyzes this scenario through the lens of a Real-World Lead Developer.

For DVA-C02 candidates, the confusion often lies in choosing between asynchronous pub/sub and message queue invocation models. In production, this is about knowing exactly how to guarantee that multiple Lambda functions trigger independently when events are published once, ensuring failure in one function won’t block others. Let’s drill down.

The Certification Drill (Simulated Question)

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Scenario

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Imagine you are leading the backend development for ShopFlux, a rising e-commerce startup. During flash sale events, the platform must reliably notify three different third-party payment reconciliation and analytics providers simultaneously. Each third-party integration requires complex processing logic, so you implemented three separate AWS Lambda functions, each encapsulating the distinct business rules for its respective partner system. The key challenge is that if one Lambda fails during processing, it must not prevent the others from executing successfully. All three integrations must run independently and concurrently.

The Requirement:

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Design a solution so that all three Lambda functions invoke concurrently in response to a single sale event, ensuring that each Lambda runs independently without blocking or being affected by the success or failure of others.

The Options

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• A) Publish the sale event from the application to an Amazon Simple Queue Service (Amazon SQS) queue. Configure the three Lambda functions to poll the queue.
• B) Publish the sale event from the application to an Amazon Simple Notification Service (Amazon SNS) topic. Subscribe the three Lambda functions so that they are triggered concurrently by the SNS topic.
• C) Publish the sale event from the application to an Application Load Balancer (ALB). Add the three Lambda functions as ALB targets.
• D) Publish the sale event from the application to an AWS Step Functions state machine. Move the invocation logic from the three Lambda functions into the Step Functions state machine.

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Correct Answer

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B

Quick Insight: The Developer Imperative

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Using SNS to fan out one event to multiple independent Lambda subscribers matches the requirement for concurrent, failure-isolated execution. Each Lambda runs independently when triggered by SNS, so failures do not impact other subscribers. This decoupled pub/sub is core for parallel event-driven integration in serverless architectures.

Content Locked: The Expert Analysis

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You’ve identified the answer. But do you know the implementation details that separate a Junior from a Senior?

The Expert’s Analysis

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Correct Answer

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Option B

The Winning Logic

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Publishing a single event to an SNS topic allows the event to be fan-out to multiple subscribed Lambda functions simultaneously. SNS invokes each Lambda asynchronously and independently, so:

• Each Lambda runs concurrently without waiting on others.
• A failure or timeout in one Lambda does not affect the others.
• You achieve the “at least once” invocation semantics per subscriber.
• This pattern is simpler and more scalable than polling or state machines for this use case.

The Trap (Distractor Analysis):

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• Why not A? Using SQS with three separate Lambda pollers means the message will be consumed and deleted after the first successful poll, so the message can only be processed once by a single Lambda (not fan-out to all three). This violates the “all run independently” requirement.

• Why not C? ALBs support Lambda targets but are designed primarily for HTTP request routing, not event fan-out or pub/sub. They cannot target multiple Lambdas concurrently from one event payload.

• Why not D? Step Functions invoke Lambdas sequentially or with branching logic. Moving complex independent logic into a state machine complicates the design. Also, a failure in one state might stop execution, violating failure isolation.

The Technical Blueprint

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# Example: Creating SNS topic and subscribing Lambdas (AWS CLI)
aws sns create-topic --name saleEventTopic

aws lambda add-permission --function-name PaymentReconcileLambda \
  --statement-id sns-invoke-permission \
  --action "lambda:InvokeFunction" \
  --principal sns.amazonaws.com \
  --source-arn arn:aws:sns:region:account-id:saleEventTopic

aws sns subscribe --topic-arn arn:aws:sns:region:account-id:saleEventTopic \
  --protocol lambda \
  --notification-endpoint arn:aws:lambda:region:account-id:function:PaymentReconcileLambda

# Repeat subscription commands for the other two Lambda functions

The Comparative Analysis (Developer Focus)

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Real-World Application (Practitioner Insight)

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Exam Rule

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For the exam, always pick SNS when you see “one event needs to trigger multiple independent Lambda functions in parallel.”

Real World

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In production, sometimes SQS is preferred for guaranteed delivery with retries, but SQS is inherently point-to-point, not fan-out. SNS combined with DLQs offers an elegant event-driven approach to multiple independent processing paths.

(CTA) Stop Guessing, Start Mastering

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Disclaimer

This is a study note based on simulated scenarios for the AWS DVA-C02 exam.