Pushpin is a reverse proxy that acts as an intermediary between clients and back-end servers handling long-lived connections, such as WebSockets and Server-Sent Events. It provides a way to terminate long-lived connections from clients and means the rest of the system can be abstracted from this complexity. It effectively manages a large number of persistent connections and automatically distributes them across multiple back-end servers, optimizing performance and reliability. Our experience using this for real-time communication with mobile devices using WebSockets has been good, and we've been able to scale it horizontally for millions of devices.