Simple(?) question regarding Lambda, EC2 and user data

Hi all:

I've been digging for a while for some best practices for what I'm trying to do. I have an S3 bucket, and when an object gets added to the bucket, I want to have Lambda launch an EC2 instance. This is very straightforward, but I also want to obtain the S3 key name for the object in the user data of the new EC2 instance.

Is there a way to do this, or is the apparent absence of any documentation or best practices for this kind of scheme an indication that it's a bad architecture?

Thank you,