Is there an overview over recommender system architectures?
A great source is the personal page of Xavier Amatriain (former Head of Engineering at Netflix and Quora). There are several links at publications detailing the system and architecture of recommender systems. In particular you could take a look at this Building industrial-scale real-world recommender systems, there is also this talk Lessons Learned from Building Real­-Life Recommender Systems and this blog post System Architectures for Personalization and Recommendation