This would have been awesome to have back when I was heavy in to the UI test automation game. Our best option at that point was a spot instance EC2 fleet and analyzing commits to determine which tests would be the most valuable to run. It's awesome being able to easily run hundreds or thousands of tests in parallel, completely segmented, and pay only on demand. A fantastic use of AWS Lambda! It suddenly becomes reasonable to do full integration tests on every merge request, or even commit, and get feedback to the developer in seconds.