The Content Delivery Network: Open Connect

You don't stream video from a Netflix server in California. You stream it from a box down the street. This is the power of Open Connect, Netflix's proprietary CDN.

How Open Connect Works

1. Appliances: Netflix manufactures custom storage servers (Open Connect Appliances or OCAs). These are red boxes packed with SSDs and HDDs.
2. ISP Partnership: They give these boxes to ISPs (Comcast, Verizon, AT&T) for free. The ISPs install them directly in their local exchanges.
3. Proactive Caching: Netflix predicts what you will watch tomorrow. During off-peak hours (4 AM), they "push" the new episode of Stranger Things to the OCA in your neighborhood.
   • Result: When you press play, the data travels only a few miles. 95% of traffic never touches the public internet backbone.

Adaptive Bitrate Streaming (ABS)

Netflix doesn't just send one video file. They encode the original master into dozens of variants:

• Codecs: H.264 (older compatibility), H.265/HEVC (4K efficiency), AV1 (royalty-free).
• Resolutions: 480p, 720p, 1080p, 4K.
• Bitrates: Low, Medium, High.

This creates a matrix of files. Each file is chopped into 4-second chunks.

The Manifest

When you press play, your device downloads a Manifest file (MPD or m3u8). It lists all available chunks.

Chunk 1: [1080p-High, 720p-Med, 480p-Low]
Chunk 2: [1080p-High, 720p-Med, 480p-Low]

Client-Side Logic:

1. Device measures bandwidth (e.g., 50 Mbps).
2. Device requests Chunk 1 in 1080p-High.
3. Network dips to 2 Mbps.
4. Device requests Chunk 2 in 480p-Low to avoid buffering.
5. Network recovers.
6. Device requests Chunk 3 in 1080p-High.

High-Level Architecture

graph TD
    User[User Device]
    
    subgraph "Control Plane (AWS)"
        API[API Gateway]
        Auth[Auth Service]
        Recs[Recommendations]
        Billing[Billing]
    end
    
    subgraph "Data Plane (Open Connect)"
        OCA1[ISP Appliance (New York)]
        OCA2[ISP Appliance (London)]
        S3[AWS S3 Master Copy]
    end
    
    User -->|Login/Browse| API
    API --> Auth
    API --> Recs
    
    Recs -->|'Play Movie X'| API
    API -->|Manifest URL| User
    
    User -->|Request Video Chunks| OCA1
    
    S3 -.->|Pre-fill (Nightly)| OCA1
    S3 -.->|Pre-fill (Nightly)| OCA2

Backend Services (Microservices)

Netflix was a pioneer in Microservices. A single request to "load homepage" might fan out to 50+ services:

1. Steering Service: Decides which OCA is closest to the user.
2. Playback Service: Verifies DRM license and concurrency limits (screens active).
3. Zuul / EVC: The Gateway that handles routing and resilience.

Data Stores

• Cassandra: Used for high-volume write data like "viewing history" (bookmarks). It handles the massive throughput of millions of users scrubbing videos simultaneously.
• EVCache: A wrapper around Memcached to reduce database load.