[manigandham]

You have to fan out further then, process each file separately and aggregate the aggregates, using SQS or something else to queue up the processing.

Azure's Durable Functions have an advantage here in making extreme fan-out situations easy.

[djhworld]

We considered it, but at the time we just felt implementing map/reduce over Lambda would just introduce a more complex architecture for such a simple problem.

Maybe the recently introduced SQS->Lambda support might make it a bit cleaner, but in the end we opted for EC2.