Scaling Web Sockets involves distributing real-time messages efficiently across multiple servers or instances. Pub/Sub (Publish/Subscribe) is a pattern used to achieve this.
- Publishers: When a user sends a message through a Websocket connection, the server publishes the message to a Pub/Sub system.
- Subscribers: All server instances subscribe to the relevant channels in the Pub/Sub system. Each subscriber receives a copy of the message.
- Distribution: The Pub/Sub system ensures that the message reaches all subscribers across different servers. This allows all connected clients to receive the message.
To scale socket connections across multiple instances of your Express.js server, we use Redis Pub/Sub as a message broker. Redis provides a publish-subscribe mechanism that allows different processes or servers to communicate with each other.