[inka]

This "solution" essentially hides away long polling of the queue behind the scenes and triggers the Lambda when message shows up - and scales the poll sizes as number of messages increase and decrease. It's what you had to previously do yourself with, for example, another Lambda, but handled by AWS and hidden from you. It's not a real event-driven model, like for example triggering Lambda by SNS.

The biggest thing to notice: because your queue gets polled behind the scenes, you will still be charged for the polling requests! Even if your queue is empty most of the time, you will pay for the requests that "check" for new messages.

In other words: by simply creating a Lambda and adding SQS queue as a trigger to it, you're adding a minimal spend to your AWS bill, that it will generate whether you're using it or not.

And because the polling is hidden from you and happens "automagically", you don't have control over how often it happens and how big the polling is, so you don't have control over the bill it will generate.