Layer 3 · Go deeper · 11 min
Go deeper
Size it, build it, then make the calls an interviewer will push you on.
Back of the envelope
Size it up
Tap through each step of the arithmetic.
How big is the whole playable catalogue?
Can one night’s fill carry a whole new season?
How busy is the control plane at the evening peak?
Build-up · 5 steps
Build the high-level design
One functional requirement at a time: browse, play, resume, publish. Then mark where it breaks at Netflix scale.
Step 1 of 5
Browse a personalised homepage
The homepage is assembled, not computed. The gateway sends the request to a homepage service that reads precomputed rows, drops titles not licensed in your country and asks for one image per title.
6 interview moments
You’re the candidate
The interviewer pushes on the hard parts. Pick an approach and see how it holds up.
Deep dive 1 of 6
Interviewer
“The evening peak is about 150 Tbps of video. Where should those bytes come from?”
Your move. Pick an approach:
Deep dive 2 of 6
Interviewer
“About 14,000 plays a second. How does each one reach a healthy appliance that has its files?”
Your move. Pick an approach:
Deep dive 3 of 6
Interviewer
“A hit is streamed for tens of millions of hours. How do you build its bitrate ladder?”
Your move. Pick an approach:
Deep dive 4 of 6
Interviewer
“A whole cloud region has a bad day. How do new plays, homepages and resumes keep working?”
Netflix set an internal goal of 99.99%, under an hour of downtime a year.
Your move. Pick an approach:
Deep dive 5 of 6
Interviewer
“Progress pings hit 625k writes a second, about nine per read. Where does viewing history live?”
Your move. Pick an approach:
Deep dive 6 of 6
Interviewer
“Suppose 10M members press play on a new season in its first 10 minutes. How do you launch it?”
That is ≈ 16.7k extra play starts a second and 40 Tbps of extra video.
Your move. Pick an approach:
Build-up · 6 steps
Follow a play, then a night’s fill
The cloud holds every decision and every piece of member data; the edge holds the bytes. Encoding and fill connect them, days before anyone presses play.
Step 1 of 6
Browse
The gateway routes to a homepage service that assembles precomputed rows, filters them to titles licensed in your country and picks one image per title. Images and metadata are cached aggressively.