How to store connections?

Question

Node.js

There is a route that accepts the user ID and in response gives a stream with which changes for the user will be streamed. I need to somehow store all these streams. I thought in the object and the key to make the user ID, but the user can connect from some other device and it will override the first connection. How to be?
There are 5 application clusters and one for streaming. For the signature on the stream, the usual http GET is used. With any change in the model on one of the clusters, it notifies the server with streams (hereinafter SS) about the change, the SS, in turn, processes what it receives in accordance with all signatures and streams the data. The problem is that one user can subscribe from several machines and by his ID I will have an array of connections. I need to add some unique identifier to them so that they can be recognized without problems.