Online Whiteboard — Detailed

flowchart TB
  subgraph Clients
    CV([Canvas client])
    CUR[Cursors]
    TOUCH[Touch / stylus]
  end

  subgraph Edge
    WS[WebSocket]
  end

  subgraph Engine
    SVR[Per-board server]
    CRDT[CRDT - shapes + properties]
    OPSTREAM[[Op stream]]
    PRESENCE[[Presence pub/sub]]
    SNAP[Snapshots]
  end

  subgraph Storage
    BOARD[(Board state)]
    HIST[(History)]
    ASSET[(Image / sticker assets + CDN)]
  end

  subgraph Features
    TPL[Templates]
    VOTE[Voting / dot voting]
    TIMER[Timer]
    EMBED[Embedded media / iframes]
    EXPORT[Export PNG / PDF]
    INF[Infinite canvas, zoom]
  end

  Clients --> WS --> Engine --> Storage
  Features --- Engine

    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 CV client;
    class CUR,TOUCH,WS,SVR,CRDT,SNAP,TPL,VOTE,TIMER,EMBED,EXPORT,INF service;
    class BOARD,HIST,ASSET datastore;
    class OPSTREAM,PRESENCE queue;

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	CDN	edge caching for static assets	cdn
HLD	Pub/Sub & message brokers	topics, consumer groups, delivery semantics	pub-sub-pattern
HLD	CRDTs	commutative replicated data types	crdts
HLD	Realtime protocols	WS / SSE / polling / gRPC streaming	realtime-protocols