How Do I Update Rails Servers from another Rails Server?

I have a Rails Server A in Country A, Rails Server B in Country B, and Rails Server C in Country C, all using Devise and Omniauth.

A user can sign up in all 3 servers. But when he logs in to Server A, that server should update Server B and C, updating the user's record there that he is currently logged into Server A. How can I do this in Rails? I've heard that this process requires interprocess communication and RPC and that RabbitMQ could be used for it. 

What do I need to implement this feature?

 

Rather than doing something complicated with RPC and all that, why not just have Server A make a POST request to an API on Server B and C? You could simply POST the same data changed over to those and make the same update. That's what I would probably do.