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
A lot of people have given some good answers. I think there is a bit more to it than just that CDNs exist and they are close to you. That is still true, but there is more.
Think of a large billboard or sign that everyone wants to read. At first, it doesn’t matter if 10 or 100 people try to read it, the sign can let everyone read at the same time. They don’t even have to read the same part of the same time. Its just there. This is how reading a movie file works on the internet.
Now imagine this was really important information on this billboard and thousands of people come to read it (network bandwidth). They all get in each others way and the people in the back are too far to see the words. They need to wait their turn to get closer. This is the network bandwidth. The bandwidth can handle a lot of connections, but will eventually get clogged up.
Now imagine this billboard was copied to different parts of the city. You just go to the one closest to you. This is the Content Distribution Network (CDN). Now the thousands of people are spread out over 10 different identical copies of the billboard so they can read it without getting in each others way.
Now, let’s say that this is a really really popular billboard. Millions of people want to read it. The message on the billboard is long and takes a while to read. Even with the 10 identical copies, people are still waiting in the back for the people in the front to finish. To help, they split the billboard into 20 smaller billboards. There are still 10 areas in the city that they have this billboard, but each of these 10 areas now has 20 smaller billboards spread out. You walk up and read the first one. You then walk to the next one when you are done. People can start reading a lot faster because the traffic moves on as they read the entire message. Netflix will split a movie into chunks, you download a few at a time, then the netflix app only asks for more chunks if you are ready. Slow readers (slow internet speed) can take their time and not cause a lot of issues. People who don’t finish reading the billboard (movie) can just walk back up to the chunk they left off, without having to start at the beginning.
Hope this is all clear… kinda longer than I thought it would be.
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