How to use Redis pub/sub to handle socket.io sessions across multiple instances?

1 point

4 years ago

When we use socket.io we are generally trying to publish messages to all the collaborators of the workspace in an application even though the origin of the message was one of the collaborator specially in a collaborative application.

In this scenario where a server must convey its message to multiple users, a socket client creates a room and adds users to this room. when any change (like app update , new comment) happens in this room that particular change must be conveyed to all the members of the room.

The information, that there is a room called xyz and there are some collaborators say a, b, c in the room is stored by a socket instance on a particular server instance.

When multiple instances of the application or server are created a new instance of socket is also created for the new instance of application. Now, when the changes of a room comes to this server this instance does not know about the room created by previous instance and also does not know about the members / collaborators of the room. Therefore new server instance can’t send the changes to those connected to the existing server. I have tried to explain the problem visually here. Read more here - https://sosha.hashnode.dev/how-to-use-redis-pubsub-to-handle-socketio-sessions-across-multiple-instances