What simple docker image/standalone projects allow you to update a file on the client page when you update on the server?

Question

AJAX

I have an idea for a project where an application inside a container will use selenium. Since there will be no access to the gui, I would like to save the current screenshot (or rather, several, but this is my problem).
I plan to connect something very lightweight (most likely it will only spin in the local network) to be able to view the current screenshot.
What can be used to automatically send a new screenshot to the user without forcing them to refresh the page every 5 seconds? I really don’t want to write my own mini-server, and it seems that such a bike should already be created.