I'm a big fan of Firebase - one of my projects uses it pretty extensively. It does exactly what your looking for I think - the ability to real time update all users when any action is taken be it new article posted, someone signs in or a comment is made, etc...
The free tier can get you pretty far and the lowest tier is $50 / month so pretty reasonable.
Using Firebase removes the need for SocketIO - Firebase roughly wraps all that and makes it easy to use.