Is dodging those HTTP POST fees the value-add over simply using the S3 HTTP API yourself ?
> Storage
> You will be billed separately for charges associated with Amazon S3 and Amazon Redshift usage including storage and read/write requests. However, you will not be billed for data transfer charges for the data that Amazon Kinesis Firehose loads into Amazon S3 and Amazon Redshift. For further details, see Amazon S3 pricing and Amazon Redshift pricing.
But to me it wouldn't make much sense to use Kinesis Firehose unless the fees were cheaper than what it would cost to utilize AWS Lamdba for the same work. I mean it can't be all that many lines of nodejs code to pop events off a stream, flush them into a tempfile in batches, HTTP POST those batches to S3 with appropriate error handling/retry logic.
Admittedly I haven't crunched the math but just by eyeballing their pricing I suspect it may be more expensive than using your own lamdba. I wonder if Kinesis Firehose is implemented internally as an AWS Lambda, it wouldn't surprise me.
I suppose that eventually the pricing on this service will drop once someone open sources such a lamdba, especially since installing a lambda is so remarkably simple.