I'm currently working on a project that's implementing this whole pattern using AWS. 1.) Requests are written to a DynamoDB table 2.) a Lambda subscribes to the

I'm currently working on a project that's implementing this whole pattern using AWS. 1.) Requests are written to a DynamoDB table 2.) a Lambda subscribes to the Dynamo event stream 3.) each event from the stream causes the Lambda to make an async call to an external system 4.) A message (with a delay) is sent to SQS from the Lambda that the async call has been made 5.) Another Lambda reads from the SQS queue and updates the original DynamoDB record completing the loop. The delay in the queue simulates a polling interval to the external system and when a successful response is returned from the external system the Dynamo record is updated with a status telling the Lambda subscribing to the event stream that "the loop" is done. This setup has to run at fairly significant peak loads and we're relying on Amazon to provision resources reliably enough to pull this off. None of us know if this will work but in terms of abstracting away the complexities of async/concurrent processing it's a novel approach.