Eli5: what happens on the server when one selects to watch a movie on Netflix and how the architecture allows 500k other people to watch the same movie almost concurrently?
In: Technology
Content Distribution Networks (CDN for short) are used. Basically, you request to watch a film on Netflix, then Netflix responds with “Sure, here is your film!” – behind the scenes, a CDN that is located near you will provide the actual data for that film to you.
500k people can watch the same film at the same time from Netflix, but the data that is sent to those 500k people will be coming from 1 of the many, many CDNs that Netflix own.
Two words: caching and locality. Streaming services like Netflix have smaller servers scattered all around the world that serve content to the users geographically close to them.
If a user requests a movie that isn’t cached on their nearest server, that server can ask around and receive a copy from somewhere else in the CDN.
First of all, not everyone stream simultaneously in perfect sync. You would watch and I start a few minutes late and we would be watching different parts of the same video.
Content in stored close to you using a technology called CDN, also close to anyone watch it. If you are lucky you may be in the same city. You just download from a close point.
Also since video streaming is a one way thing unlike video chat, they can use faster protocols.
One nice fact is Netflix stores multiple copies of the same movie in different qualities and switches between them according to your streaming speed. According to their research a %7 change in quality is not noticed, so quality can change you without even noticing.
They put their own cache servers into ISP’s too. They have or had a page to request them. It’s a win win, as netflix gets content closer to their customers, and ISP doesn’t pay for the traffic on the internet side.
Page still there, it’s their open connect appliance.. “Our appliances are provided free of charge for ISP partners who meet our basic requirements, but they are not for sale to other parties.”
the question to be asked is, how are they steaming hundreds of thousands of different shows being streamed concurrently, which I guess is the same as the replies here which is CDN and satellite servers
Across the world Netflix has thousands of cheap servers with a lot of storage whose only job is to handle downloads.
Two people don’t stream the _same_ movie file. The server lets them each download their own copy of the file _as they are watching it_.
Streaming is just watching the parts of a movie you’ve already downloaded while you’re downloading it. Buffering is when you catch up to what you’ve downloaded.
In addition to what has already been mentioned, Netflix doesn’t put their whole catalog into CDN and cache. They would bankrupt themselves if they tried to do that. The clever part is guessing which films and content to cache where in a way that minimizes latency access the whole system.
Straight statistics helps, but being able to predict which films individuals will want to watch with better accuracy than the overall statistics is how they make money. They improve their bottom line by saving money on storage and bandwidth.
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For the technical gurus, netflix is using docker they have published several time about this https://netflixtechblog.com/the-evolution-of-container-usage-at-netflix-3abfc096781b
This is nearly an hour but it does detail some of the many microservices that let Netflix work.
Apologies I only have a YouTube link.
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