Scaling WebSockets with a Pub/Sub Backplane
Learn how to broadcast WebSocket messages across multiple FastAPI instances using a Redis pub/sub backplane.
The Multi-Instance Problem
A single FastAPI process can hold WebSocket connections in memory. But in production you run multiple instances behind a load balancer.
A message arriving on instance A cannot reach a client connected to instance B unless the instances share state.
What is a Backplane?
A backplane is a shared messaging channel that every instance subscribes to. When one instance receives an event, it publishes to the backplane and all instances relay it to their local clients.
All lessons in this course
- WebSocket Protocol Fundamentals
- Implementing WebSockets in FastAPI
- Building a Real-time Chat Application
- Scaling WebSockets with a Pub/Sub Backplane