The author covered this: >>> Is Spotify really paying $290,518/month? >>> Of course, for such a high profile customer and for the priviledge of a case study,

The author covered this: >>> Is Spotify really paying $290,518/month? >>> Of course, for such a high profile customer and for the priviledge of a case study, we can assume Spotify has some heavy discounts. Cost is important but using public cloud and especially managed services like pub/sub, the biggest benefit is in ease of deployment and not having to manage/scale everything.