At least part of their content delivery network is based on their own hardware/software (see https://openconnect.netflix.com/en/ and the PDF referenced there). It's called "Open Connect Appliance".

They use AWS for video transcoding) (see http://techblog.netflix.com/2015/12/high-quality-video-encod...) and probably other activities (analytics, business)

adrian cockcroft, who now works for aws, is known for a lot of his very early forward thinking approach to distributed applications and was responsible for their cloud architecture. I highly recommend checking out his medium and twitter, he's a brilliant man.

I've heard they're looking at 'architecture in a box' solutions, which would allow them to abstract designs from specific cloud providers and perform cloud arbitrage; eg, if Cloud Provider X can run the app at 14c/hour, and Cloud Provider Y can run the app at 22c/hour, then they can just deploy the entire architecture on Cloud Provider Y.

They were fairly early and fairly vocal proponents of moving to cloud based systems. I haven't looked in awhile but last I checked all but their CDN was running on AWS.