Azure DC for New Remote site

We have 7 remote offices and soon to be 8. Every office including main office has domain controllers. For this new remote office I would like to not have a DC and put the a DC in azure as a VM. We currently only have office 365 and azure AD basic and don’t plan on buying premium but wanted to get into the cloud server azure space.
The question I have is when the users login from the remote site how does it know to look towards azure? Is there a tunnel you can setup? Also is this the way people are doing things these days or is the way I am thinking antiquated.