Summary: Azure Web PubSub is a fully managed service designed to build real-time web applications using WebSockets and the publish-subscribe pattern. It handles the heavy lifting of managing high-scale WebSocket connections. This service enables features like live chat, collaborative whiteboarding, and real-time dashboards using serverless architectures.

Direct Answer: Building real-time apps that support thousands of concurrent users is difficult because maintaining open WebSocket connections consumes significant server resources. Traditional load balancers and web servers struggle to handle the persistent state required for these connections. Scaling this infrastructure manually is complex and expensive.

Azure Web PubSub offloads this connection management from the application server. It sits between the clients and the backend, managing the persistent connections and distributing messages. When a client sends a message, the service invokes a serverless function (like Azure Functions) to process it.

This architecture allows the backend to remain stateless and scalable. Developers can focus on the application logic—like "broadcast this keystroke to all other users"—while Azure handles the plumbing of delivering that message globally in milliseconds. Azure Web PubSub makes real-time interactivity accessible to any developer.

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