Serverless Payment App: Lambda & ECS Fargate for Least Overhead

SAA-C03 By islever Editorial Last updated

Design secure workloads and applications. Design cost-optimized compute solutions.

Short answer

D Use API Gateway and Lambda for validation and ECS with Fargate for the long-running backend to ensure zero infrastructure management.

Question

A company wants to run its payment application on AWS. The application receives payment notifications from mobile devices. Payment notifications require a basic validation before they are sent for further processing. The backend processing application is long running and requires compute and memory to be adjusted. The company does not want to manage the infrastructure. Which solution will meet these requirements with the LEAST operational overhead?
  1. Create an Amazon Simple Queue Service (Amazon SQS) queue. Integrate the queue with an Amazon EventBridge rule to receive payment notifications from mobile devices. Configure the rule to validate payment notifications and send the notifications to the backend application. Deploy the backend application on Amazon Elastic Kubernetes Service (Amazon EKS) Anywhere. Create a standalone cluster.
  2. Create an Amazon API Gateway API. Integrate the API with an AWS Step Functions state machine to receive payment notifications from mobile devices. Invoke the state machine to validate payment notifications and send the notifications to the backend application. Deploy the backend application on Amazon Elastic Kubernetes Service (Amazon EKS). Configure an EKS cluster with self-managed nodes.
  3. Create an Amazon Simple Queue Service (Amazon SQS) queue. Integrate the queue with an Amazon EventBridge rule to receive payment notifications from mobile devices. Configure the rule to validate payment notifications and send the notifications to the backend application. Deploy the backend application on Amazon EC2 Spot Instances. Configure a Spot Fleet with a default allocation strategy.
  4. Create an Amazon API Gateway API. Integrate the API with AWS Lambda to receive payment notifications from mobile devices. Invoke a Lambda function to validate payment notifications and send the notifications to the backend application. Deploy the backend application on Amazon Elastic Container Service (Amazon ECS). Configure Amazon ECS with an AWS Fargate launch type. Correct Answer

Key Takeaways

The exam traps candidates by offering managed services like EKS or EC2; the key is recognizing that 'no infrastructure management' strictly requires serverless options like Fargate and Lambda.

This question tests designing a serverless architecture using AWS Lambda for validation and Amazon ECS with Fargate for long-running backend processing to minimize operational overhead.

Common mistake: Candidates often choose EKS (Option B) because it is a popular managed service, but self-managed nodes or even standard EKS require more operational effort than Fargate.

Expert Analysis

Why the Answer Is Correct

The correct solution is D because it leverages fully managed, serverless AWS services to meet the 'least operational overhead' requirement. Amazon API Gateway handles the ingestion of mobile notifications, while AWS Lambda performs the basic validation without requiring server management. For the long-running backend process, Amazon ECS on AWS Fargate allows compute and memory adjustments without managing any underlying servers (EC2 instances), perfectly aligning with the constraint.

Why the Other Options Are Wrong

Option A uses EKS Anywhere, which involves on-premises clusters and significant operational overhead. Option B uses EKS with self-managed nodes, requiring the company to patch and manage the EC2 instances in the cluster. Option C uses EC2 Spot Instances, which are raw compute resources that the user must provision, scale, and maintain, violating the 'do not want to manage the infrastructure' requirement.

Community Comment Notes

The community unanimously agrees with D, citing that Fargate is the only truly serverless compute option among the choices. As Mikado211 noted, 'No infrastructure == not C least overhead == ECS better than EKS'. Comments highlight that Lambda is ideal for short validation tasks and Fargate for long-running jobs, confirming the architectural pattern.

Exam Strategy

When you see 'do not manage infrastructure' or 'least operational overhead', immediately eliminate any option containing EC2, EKS (unless explicitly Fargate-only context implies otherwise, but usually EKS implies node management), or self-managed databases. Prioritize Lambda, Fargate, RDS/Aurora Serverless, and DynamoDB.

Frequently Asked Questions

Why not use SQS instead of API Gateway?

API Gateway is preferred for receiving HTTP requests from mobile devices directly. SQS is typically used for decoupling microservices or background job queues, not as the primary ingress point for mobile apps.

Is EKS Everserverless?

Standard EKS requires managing worker nodes (EC2). While EKS on Fargate exists, Option B specifies 'self-managed nodes,' making it operationally heavy compared to pure ECS Fargate.

More SAA-C03 FAQ →

Community Votes

D
100%

100% of anonymous learners picked answer D. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 6 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 6

  1. Mikado211 👍 5 Answered D
    We want to have least overhead and no infrastructure (aka no server). So no infrastructure == not C least overhead == ECS better than EKS == not B and not A Fargate is serverless so D is still valid. So the answer is D.
  2. sandordini 👍 2 Answered D
    Lot of grip in this question, but to keep it short: No infra: B, C Out. EKS Anywhere: Onprem + AWS: Not needed. ECS Fargate: Serverless, Least Ops Overhead, SQS fine for the queue, Lambda good for basic validation.
  3. Cpso 👍 2 Answered D
    D= less operation. But should have SQS to buffer a job.
  4. Scheldon 👍 1 Answered D
    AnswerD I would go with Lambda function to do basic validation it should not take more then 15min hence Lambda is perfect for that job. Then we have information that backend processing application is long running and we need to make compute and memory adjustment, and everythink need to be automatic as company do not want to manage infrastucture. In that situation Fargate with ECS will be ideal as it can run background application for every paymant separetly we need only adjust amunt of resources in use. More payments more application running, mmore resources in use and oposite,
  5. seetpt 👍 4 Answered D
    D is correct
Show 1 more comment
  1. asdfcdsxdfc 👍 3
    shouldn't it be D?

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