How to send data received via ajax request through Socket.io?

Question

Node.js

Good afternoon. It is necessary to open a modal in the browser on a signal from an external service. I decided to do it on sockets, the way is that when a POST request comes to a certain address, you need to determine which user to show the modal, and actually execute emit.
But I don't understand how to send data to the socket from the middle of the post request handler (I use express).

Answer 1

Inside the POST handler, you need to somehow notify the socket handler to send a message.
Within the same process, this can be done using events - read about EventEmitter.
If the processes are different, then you need to notify differently. The first and simplest thing that came to mind was something like queues (RabbitMQ) or, more lightweight, Pub/Sub (Redis)