Why Do We Need Socket.IO Scaling?
So far, our application has used a single Node.js server instance.
All connected sockets are maintained within that server process.
Consider what happens when you deploy two Node.js instances behind a load balancer.
- User A connects to Server 1.
- User B connects to Server 2.
- User A sends a message.
- Server 1 broadcasts the message using its local Socket.IO instance.
Without a shared adapter, Server 2 does not automatically receive the broadcast.
This happens because the default Socket.IO adapter stores room and socket communication state locally within each server process.
To solve cross-instance communication, we need an adapter that distributes broadcasts between server instances.
Problem Without Shared Adapter
Key Takeaways
The default adapter is local to a server instance.
Multiple server instances do not automatically share broadcasts.
A distributed adapter enables cross-instance event communication.