At imgix, we are building the "graphics card" for the Internet. We provide image and visual media processing on-demand via a URL-based API. We connect to a customer's existing images (e.g. S3 bucket) and then provide a domain they can use to access those images dynamically, creating any number of sizes, crops, adjustments, and other variants of those images. Think of it like Photoshop's "Save for Web" feature but for a million images at a time.
We maintain two separate technology stacks, one designed to perform all of the image processing we do and one for configuring those image processing pipelines for customers. Our image processing infrastructure is built using technologies such as haproxy, varnish, Lua, Go, Objective-C and C++. It handles >100K qps of requests and >10K qps of image renders. Our configuration and customer management stack is built on Python, Mongo, mySQL, nodejs, and Angular.