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Question 26

A developer is creating an application that will be deployed on IoT devices. The application will send data to a RESTful API that is deployed as an AWS Lambda function. The application will assign each API request a unique identifier. The volume of API requests from the application can randomly increase at any given time of day.

During periods of request throttling, the application might need to retry requests. The API must be able to handle duplicate requests without inconsistencies or data loss.

Which solution will meet these requirements?

Create an Amazon RDS for MySQL DB instance. Store the unique identifier for each request in a database table. Modify the Lambda function to check the table for the identifier before processing the request.

Create an Amazon DynamoDB table. Store the unique identifier for each request in the table. Modify the Lambda function to check the table for the identifier before processing the request.

Create an Amazon DynamoDB table. Store the unique identifier for each request in the table. Modify the Lambda function to return a client error response when the function receives a duplicate request.

Create an Amazon ElastiCache for Memcached instance. Store the unique identifier for each request in the cache. Modify the Lambda function to check the cache for the identifier before processing the request.

Correct Answer: B

To handle duplicate API requests without inconsistencies or data loss, creating an Amazon DynamoDB table to store the unique identifier for each request is the best solution. DynamoDB offers strong consistency and provides the necessary mechanisms to check for duplicates before processing. This helps ensure the data remains consistent even if the application retries requests due to throttling. Additionally, DynamoDB is well-suited for the unstructured data typically generated by IoT devices, and its scalability can handle the variable volume of API requests effectively.

Discussion

Devon_FazekasOption: B

I originally thought ElastiCache would provide the sufficient session management of the unique identifiers with the least latency. But apparently, the scope of this question revolves around durability, not latency. Hence, a persistent storage is better suited. And while RDS is a viable solution for durability and performance, the question specifies IoT devices which typically produce unstructured data that is better handled by No-SQL services like DynamoDB.

UntamablesOption: B

B The resolution is to make the Lambda function idempotent. https://repost.aws/knowledge-center/lambda-function-idempotent https://aws.amazon.com/builders-library/making-retries-safe-with-idempotent-APIs/

Tony88Option: B

Cache topic. So Elastic Redis and DynamoDB both can be used as a cache solution. If you want high performance, low latency, go with Redis If you want persistent storage, go with DyanmoDB.

ElFaramawi

Why not C? According to the question "During periods of request throttling, the application might need to retry requests", this indicate that lambda should returns client error, so the application can make another retry request to fix the problem

cocolavayen

same doubt

queekao

because c don't mention about retry actions

65703c1Option: B

B is the correct answer.

Abdullah22Option: B

Consistency: Memcached does not provide built-in support for atomic operations or conditional writes like DynamoDB does. Handling duplicate requests and ensuring consistency would require additional application logic and complexity.