⚡ Real-time Systems

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┌─────────────────────────────────────────────────────────────┐
│                     Load Balancer                            │
│              (Sticky sessions if needed)                     │
└─────────────────────────────────────────────────────────────┘
                              │
        ┌─────────────────────┼─────────────────────┐
        │                     │                     │
┌───────▼───────┐   ┌─────────▼─────────┐   ┌───────▼───────┐
│  WS Server 1  │   │   WS Server 2     │   │  WS Server 3  │
│  (Stateless)  │◄──┼───────────────────┼──►│  (Stateless)  │
└───────────────┘   └───────────────────┘   └───────────────┘
        │                     │                     │
        └─────────────────────┼─────────────────────┘
                              │
                    ┌─────────▼─────────┐
                    │   Redis Pub/Sub   │
                    │  (Cross-server)   │
                    └───────────────────┘

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// Decision framework
const chooseProtocol = (requirements) => {
  if (requirements.bidirectional && requirements.lowLatency) {
    return 'WebSocket';  // Chat, gaming, collaboration
  }
  if (requirements.serverPush && !requirements.clientPush) {
    return 'SSE';  // Notifications, feeds
  }
  if (requirements.peerToPeer && requirements.media) {
    return 'WebRTC';  // Video calls, screen share
  }
  if (requirements.iot && requirements.lowOverhead) {
    return 'MQTT';  // Sensors, embedded devices
  }
  return 'Polling';  // Fallback for simple cases
};

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// Room-based scaling
class VideoRoom {
  async join(user, socket) {
    const room = await this.getOrCreateRoom(user.roomId);
    
    if (room.participants.length < PEER_LIMIT) {
      // Small room: peer-to-peer mesh
      return this.joinPeerMesh(room, user, socket);
    } else {
      // Large room: route through media server
      return this.joinMediaServer(room, user, socket);
    }
  }
}