I don’t have much experience with the Amazon Lambda service, but I was checking it out and it looks like a more advance approach of the one implemented by webtask.io.
You can use node.js, java or python which gives you more options (webtask.io is just node), so basically is a more complete solution that can be easily integrated with the already existing amazon services.
Update: It also provides a granular control for the Access control and security, it looks interesting.
Thanks for point me out this, gonna check it out for sure. they have a nice FAQ https://aws.amazon.com/lambda/faqs/