Fascinating stuff... the latest architectural overview is particularly interesting (http://www.slideshare.net/adrianco/netflix-architecture-tuto...) If I had one criticism, I'd love to see a separate overview of the fundamental (CS?) problems, vs. the ephemeral engineering problems (AWS). We all know AWS will go the way of the mainframe (though we may disagree as to timeframes!), but I think e.g. content recommendation algorithms and architectures will forever remain an interesting problem.
Though I'd love to see the monitoring solution open-sourced :-)
Monitoring is done with two systems, one in-house in-band that we might open source one day (was called Epic, currently called Atlas). The other is AppDynamics running as a SaaS application with no dependencies on AWS. There is some useful overlap for when one or the other breaks, we merge the alerts from both (plus Gomez etc) but they have very different strengths as tools.
I ran one of the recommendation algorithm teams for a few years before we did the cloud migration. The techblog summaries of the algorithms are pretty good. The implementation is lots of fine grain services and data sources, changing continuously. Hard to stick a fork in it and call it done for long enough to document how it works.
Though I'd love to see the monitoring solution open-sourced :-)