Netflix Streaming, the whole design.

%% title: Netflix on one page: AWS decides, Open Connect delivers
flowchart TD
  CL@{ icon: "sd:tv", label: "Clients<br/>TV · phone · tablet · web · console" } -->|"browse · press play"| ZU@{ icon: "sd:gateway", label: "Zuul API gateway<br/>auth · rate limit · routing" }
  ZU --> MS["Control plane on AWS · 1,000+ services<br/>catalog · reco · search · billing<br/>every call behind a circuit breaker"]:::core
  ZU ==> PB["Playback service<br/>entitlement · DRM · manifest"]:::hot
  MS --> EV@{ icon: "sd:cache", label: "EVCache<br/>API responses" }
  MS --> CS@{ icon: "tech:cassandra", label: "Cassandra<br/>users · viewing history" }
  MS --> MY@{ icon: "tech:mysql", label: "MySQL<br/>billing" }
  PB -.->|"playback URLs · ranked OCA list"| ISP
  ENC["Encoding pipeline<br/>per-title ladder · ~30 versions · 2–4 s chunks"]:::service --> ORI@{ icon: "tech:s3", label: "Origin · S3<br/>full library · ~360 TB" }
  ORI -.->|"nightly fill"| IXP@{ icon: "sd:server", label: "IXP appliances<br/>most of the catalogue" }
  IXP -.->|"off-peak fill · predicted popular"| ISP@{ icon: "sd:server", label: "ISP-embedded appliances<br/>18,000+ servers · 90 %+ hit" }
  ISP ==>|"video chunks"| PL@{ icon: "sd:users", label: "Player<br/>ABR picks a rung per chunk" }
  class CL,PL client
  class ZU edge
  class EV,IXP,ISP cache
  class CS,MY,ORI store

%% title: The player's ABR loop: pick a rung for the next chunk
flowchart TD
  CH["Chunk downloaded<br/>size ÷ time = throughput sample"]:::service --> BW["Bandwidth estimate<br/>harmonic mean of last 5 samples"]:::core
  BW --> B{"Seconds buffered?"}
  B -->|"< 5 s · panic"| LOW["Drop straight to the lowest rung"]:::bad
  B -->|"5–15 s · low"| HOLD["No step up<br/>step down if needed"]:::queue
  B -->|"healthy"| UP{"Highest rung with<br/>bitrate × 1.2 ≤ estimate"}
  UP -->|"10 s since last switch"| SW["Switch at next chunk boundary"]:::ok
  UP -->|"inside cooldown"| KEEP["Up blocked · down allowed"]:::service

%% title: Press play: manifest from AWS, chunks from the ISP
sequenceDiagram
  autonumber
  participant P as Player
  participant Z as Zuul
  participant S as Playback service
  participant O as ISP appliance
  P->>Z: Play title X · profile · device
  Z->>S: Authorise playback
  Note over S: entitlement · device capabilities · DRM
  S-->>P: Manifest · bitrate ladder · ranked appliance URLs
  P->>O: GET chunk 1 at 480p
  O-->>P: 2–4 s of video
  Note over P: pre-buffer ~5 s, then play · under 2 s
  loop every chunk
    P->>O: Next chunk at the rung ABR picked
    O-->>P: Chunk
  end

%% title: Appliance dies mid-stream: fail over from the manifest
sequenceDiagram
  autonumber
  participant P as Player
  participant O as ISP appliance
  participant X as IXP appliance
  P->>O: GET chunk 41
  O--xP: timeout
  Note over P: no new API call · next URL is already in the manifest
  P->>X: GET chunk 41 (next in ranked list)
  X-->>P: Chunk 41
  alt buffer still healthy
    Note over P: keeps quality, viewer sees nothing
  else buffer below 5 s
    Note over P: ABR drops a rung · brief quality dip, no freeze
  end

%% title: Recommendations fail: the homepage degrades, not breaks
sequenceDiagram
  autonumber
  participant C as Client
  participant R as Reco service
  participant M as ML models
  C->>R: Homepage rows for profile
  R->>M: Personalised rows
  M--xR: error (3rd in a row)
  Note over R: breaker OPEN · stop calling ML
  R-->>C: Popular titles (fallback)
  alt after the timeout · HALF_OPEN
    R->>M: Trial call
    M-->>R: ok · closes after enough successes
  else trial fails
    Note over R: back to OPEN · timeout restarts
  end

%% title: Core entities
classDiagram
  class Title {
    +titleId : string
    +runtime : minutes
    +genres : list
    +maturityRating : string
  }
  class Encode {
    +resolution : 240p to 4K HDR
    +bitrate : kbps · per-title ladder
    +codec : string
  }
  class Chunk {
    +index : int
    +duration : 2 to 4 s
    +url : string
  }
  class Profile {
    +profileId : string
    +accountId : string
    +parentalLevel : string
  }
  class ViewingRecord {
    +profileId : string
    +titleId : string
    +resumeAt : seconds · Continue Watching
    +watchedAt : timestamp
  }
  class Appliance {
    +ocaId : string
    +tier : ISP or IXP
    +capacity : up to 120 TB
    +cachedTitles : set
  }
  Title "1" --> "many" Encode : ~30 versions
  Encode "1" --> "many" Chunk : aligned boundaries
  Profile "1" --> "many" ViewingRecord : history
  ViewingRecord "many" --> "1" Title : of
  Appliance "many" --> "many" Encode : holds copies

%% title: Playback session state machine
stateDiagram-v2
  [*] --> REQUESTED
  REQUESTED --> DENIED: not entitled
  REQUESTED --> AUTHORIZED: manifest issued
  AUTHORIZED --> PREBUFFERING: fetch first chunks at 480p
  PREBUFFERING --> PLAYING: ~5 s buffered
  PLAYING --> PANIC_LOW: buffer below 5 s
  PANIC_LOW --> PLAYING: buffer refilled
  PLAYING --> FAILING_OVER: appliance unreachable
  FAILING_OVER --> PLAYING: next appliance in list
  PLAYING --> REBUFFERING: buffer empty
  REBUFFERING --> PLAYING: chunk arrives
  REBUFFERING --> ABANDONED: viewer quits
  PLAYING --> ENDED: resume point saved
  ENDED --> [*]
  DENIED --> [*]
  ABANDONED --> [*]
  class ENDED ok
  class DENIED,ABANDONED bad
  class PANIC_LOW,FAILING_OVER,REBUFFERING queue