This definitely looks interesting for using with S3/Lambda, but it's not up-to-date to the latest thumbor version[0], and not sure if it's most cost-effective at larger scales.

In any case, my main point was that there are plenty of great options for resizing/manipulating images on-the-fly rather than pre-processing :) how you choose to deploy it is secondary.

[0] it's providing thumbor 6.4.2, and the latest is 6.5.1 (I'm pretty sure it's possible to upgrade though)