I don't understand how all the recommendation engine stuff really needs to be in the critical path; 99% of the time, netflix behavior I observe (admittedly, sample size of 2) is "watch next episode of same series." And new series are discovered via referral from someone else, or googling e.g. "post apocalyptic sci fi movies", then figuring out what Netflix has, downloading if unavailable, or Amazoning as absolute worst case. The Netflix recommender doesn't really fit in, so all they need is authentication and authorization, a static URL distributor, and CDN.