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Open SystemDecoder on a larger screen to build systems, run simulations, and inject chaos.
Daily Challenge
SystemArena
5
Questions
Think Deep
1×
Daily Shot
5 sharp system design questions. One attempt daily — streaks, XP & leaderboard.
What's waiting for you on desktop
Live Simulations
Watch latency spike, queues fill, and nodes fail in real time. Every slider change is instant.
Visual Architecture Canvas
Drag nodes, draw edges, and build any distributed system topology from scratch.
Chaos Engineering
Kill servers, introduce packet loss, throttle CPUs — and watch your system react.
Real-time Insights
Throughput, p99 latency, error rates — all charted live as your simulation runs.
40+
Concepts
<1s
Feedback
∞
Replays
"The best way to understand a distributed system
is to break it."
Netflix
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260M subscribers. 15% of global internet traffic.
Play → Entitlement → CDN manifest → ABR stream
Request Flow
260 million subscribers
Netflix serves 260 million subscribers across 190 countries. At peak — Friday evening in the US after a big series drop — it handles over 15% of all downstream internet traffic on the planet. That's not a metaphor. ISPs plan their capacity around Netflix's usage patterns.
The core tension
Video streaming has three competing constraints: quality (4K HDR requires 25 Mbps), availability (99.99% uptime = <53 min downtime/year), and scale (millions of concurrent streams). You cannot optimise all three naively — the architecture must be partitioned by responsibility.
Three distinct systems
We'll build Netflix as three interlocking systems: (1) the + that gets video to the screen; (2) the upload and transcoding pipeline that prepares every title before it can stream; and (3) the that drives 80% of what viewers watch.
Key Insight
Netflix isn't one system — it's three systems wired together: playback (low-latency per-session), upload pipeline (high-throughput async), and recommendations (ML-driven personalisation). Each scales independently and fails without taking the others down.
Overview