CDN Service — Detailed

flowchart TB
  subgraph Users
    BR([Browser])
    APP([Mobile])
    IOT[IoT]
  end

  subgraph Steering
    GDNS[Geo DNS / Anycast BGP]
    RUM([Real-user measurement])
  end

  subgraph Edge[Edge POPs - hundreds globally]
    PRX[Edge proxy]
    L1[L1 in-RAM]
    L2[L2 SSD]
    WAF
    BOT
    EW([Edge workers / WASM])
    TLS[TLS / 0-RTT QUIC]
    LOG[Real-time logs]
  end

  subgraph Mid
    MID[Mid-tier shield]
  end

  subgraph Control[Control Plane]
    CFG[Config / routes]
    PURGE[Purge by URL / tag / all]
    CERT[Cert mgmt ACME]
    AN[Analytics]
    BIL[Billing]
    KEYS[Auth / API tokens]
  end

  subgraph Origin
    OLB[Origin LB]
    OS[Origin servers]
  end

  subgraph CustOps[Customer Ops]
    PORTAL[Dashboard]
    API[REST API]
    CLI[CLI / Terraform]
  end

  Users --> Steering --> Edge
  Edge -. miss .-> Mid -. miss .-> Origin
  Control --- Edge
  CustOps --- Control

    classDef client fill:#dbeafe,stroke:#1e40af,stroke-width:1px,color:#0f172a;
    classDef edge fill:#cffafe,stroke:#0e7490,stroke-width:1px,color:#0f172a;
    classDef service fill:#fef3c7,stroke:#92400e,stroke-width:1px,color:#0f172a;
    classDef datastore fill:#fee2e2,stroke:#991b1b,stroke-width:1px,color:#0f172a;
    classDef cache fill:#fed7aa,stroke:#9a3412,stroke-width:1px,color:#0f172a;
    classDef queue fill:#ede9fe,stroke:#5b21b6,stroke-width:1px,color:#0f172a;
    classDef compute fill:#d1fae5,stroke:#065f46,stroke-width:1px,color:#0f172a;
    classDef storage fill:#e5e7eb,stroke:#374151,stroke-width:1px,color:#0f172a;
    classDef external fill:#fce7f3,stroke:#9d174d,stroke-width:1px,color:#0f172a;
    classDef obs fill:#f3e8ff,stroke:#6b21a8,stroke-width:1px,color:#0f172a;
    class BR,APP,RUM client;
    class GDNS,OLB edge;
    class IOT,PRX,L1,L2,TLS,MID,CFG,PURGE,CERT,AN,BIL,KEYS,OS,API,CLI service;
    class EW compute;
    class LOG,PORTAL obs;

Glossary & fundamentals

Concepts referenced in this design. Each row links to its canonical page; the tag column shows whether it is a high-level (HLD) or low-level (LLD) concept.

Tag	Concept	What it is	Page
HLD	Load balancer / GSLB	L4/L7 traffic distribution and failover	load-balancer
HLD	CDN	edge caching for static assets	cdn
HLD	HTTP / TLS protocols	HTTP 1.1/2/3, QUIC, TLS 1.3	http-protocols
LLD	REST API design	verbs, statuses, pagination, errors	rest-api-design
LLD	Structural patterns	Adapter, Decorator, Facade, Proxy, Composite	structural-patterns