Download Full Version SAA-C03 Amazon Web Services Exam

The correct answer is A because the legacy mainframe requires a synchronous RESTful API and the new service takes approximately 3 minutes to complete each request. Among the choices, Amazon API Gateway REST API is the appropriate option for exposing a synchronous REST endpoint to the mainframe. API Gateway REST APIs support longer integration timeouts than HTTP APIs, which makes them more suitable for workloads that take an extended time to process. The REST API can invoke an AWS Lambda function to execute the stock price calculation and return the result synchronously.

Option B is incorrect because API Gateway HTTP APIs have a shorter integration timeout and are not the best fit for a request that takes around 3 minutes. Option C is incorrect because WebSocket APIs are not RESTful and do not meet the requirement for synchronous REST-based integration with the mainframe. Option D is incorrect because Lambda function URLs do not provide the same API management features and are not the best choice for a long-running synchronous enterprise integration requirement of this kind.

AWS design guidance favors API Gateway when exposing managed APIs to external consumers. In this case, the REST API option best matches the requirement for synchronous RESTful access while supporting the longer processing duration. It also provides a managed front door for authentication, throttling, and operational control if the company needs those features later.

One note of honesty: some exam versions treat the REST API timeout detail as the deciding factor here. That is the key reason REST API is preferred over HTTP API for this question.

TooManyRequestsException errors occur when Lambda exceeds concurrency limits. The recommended pattern is to use Amazon SQS with Lambda to decouple and buffer traffic, ensuring that bursts of requests are queued and processed smoothly. Enabling provisioned concurrency for Lambda ensures that functions are pre-initialized and ready to handle spikes in load with low latency. Step Functions (B) is designed for workflow orchestration, not high-throughput request buffering. SNS with Lambda (C) does not provide buffering and may overwhelm Lambda during bursts. Reserved concurrency (D) limits function scaling instead of improving resilience. Therefore, option A provides a scalable and resilient solution, minimizing errors during traffic surges.

To improve scalability and availability, EC2 Auto Scaling across multiple Availability Zones with an Application Load Balancer ensures resilient infrastructure. Migrating to Amazon Aurora MySQL with reader endpoints reduces read latency by offloading read traffic to replicas in otherAZs, while also increasing high availability.

The best practice for secure access control in AWS is to use IAM roles with least-privilege policies, granting only the permissions necessary to perform required tasks. Assigning roles individually ensures that developers cannot overstep their intended access boundaries.

Sharing credentials or using permanent access keys increases the risk of security breaches. Cognito is primarily intended for managing user access to applications, not AWS infrastructure. Thus, Option B best meets security and access control requirements.