So, if you have specified that traffic from the US should be routed to a particular resource, Route 53 will direct those users to that resource, regardless of where it is physically located. This means your instance in Europe will serve the users in the US as long as the geolocation policy is set correctly1.
web browser to dns server, first it goes to root dns server, then it goes to tld then sld dns, and at each step it keeps getting closer to the actual location, and the final one then is saved as a cache in the local dns server, it then goes back to web browser and from there it takes to web server:
route 53:
TTL: time to leave
In private hosted zone only within VPC reosurces communicate with each other,
FIRST EC2 instnace will ask for other one from HZ, it will reutrn a ip and that will allow it to connect with the other ec2 isntance, simialrly other ec2 asks db ka sld, and then it gets ip address in reposne and connects it with the db
