BackendWebSocketScale
Scaling real-time WebSockets to over 100,000 concurrent clients is a classic engineering problem. Unlike HTTP, WebSocket connections are stateful and persistent, which means your servers hold active sockets open.
Here is the architectural pattern that successfully scaled my event platform:
1. Redis Pub/Sub Backplane
When a client connects to Server A, but the message they need is published on Server B, you need an inter-server messaging layer. Using Redis Pub/Sub, servers subscribe to user channels and route messages internally to the right socket.
2. Connection Distributing Load Balancers
Configure AWS ALBs or Nginx with sticky sessions and a high timeout to prevent socket dropouts. Also, implement connection rate-limiting to protect the backend from "connection storms" when clients reconnect simultaneously.
3. Tuning the Linux Kernel limits
By default, Linux limits file descriptors (and sockets are file descriptors). Update `/etc/security/limits.conf` and adjust `sysctl` parameters like `fs.file-max` and `net.ipv4.ip_local_port_range` to support high connection counts per node.