SignalR is a library for .NET developers to help build real-time web-connected applications. SignalR makes use of WebSockets (http://en.wikipedia.org/wiki/WebSocket) where available, which provide duplex (two-way) communications over TCP sockets, allowing clients to send data to a server; but more importantly, it allows the server to push data back to the client, which means that clients don't need to continually poll the server for updates.

SignalR can have issues with scalability when deployed on load-balanced web servers because clients will have a connection to a single website instance and will not receive messages from other instances, which means that we end up with multiple hubs rather than just one.

There are a number of solutions to deal with scalability with SignalR using a backplane; where each hub forwards messages to the backplane rather than directly to the client, the backplane then updates all hub instances, which then forwards the message to the client...