everything in this thread is raw speculation, obv, but if i had to put money on anything i'd say this is a left-pad incident. some piece of something or other that all of these services happen to depend on went down. Second most likely seems to be some random failure of one leading to an unexpected traffic spike in others, though it seems like we've been talking about automated scalability in web apps for so long that there should at least be a response to, if not a solution for, this sort of problem.