It has to be internal because they are incredibly protective of their API (hell they sold their firehouse to just 1 darn company). My guess it's NLP type proces

It has to be internal because they are incredibly protective of their API (hell they sold their firehouse to just 1 darn company). My guess it's NLP type processing. Things like review highlights, recommendations, etc. that's probably 99% of their load. The user-centric stuff like submitting reviews, comments is trivial - as another user said , a large single instance is enough.