model's information keep in sync with external source

I will develop a new app (Maybe we choose Laravel or Rails). The point is that we will have our database with let's say user table so at level application, we will have a User model. Any change in our models we will send a notification to another external source instantly. In the future the app will allow switch the external source.

I think that a good option is create a UserService (Service layer design patter) class to wrap the logic and then all controllers will use it.

What do you think about it's the best way to do it?