There were few scenarios in which we had part of our data being published to Cloud DB (Microsoft Azure DB) for external access. One of the main requirements was to keep both databases synchronized There are couple of ways by which you can do this. I've written a blog on this based on my project experience.
Hope this will be helpful for someone who has similar requirement.
Feel free to read through and give your comments. You can reach me for any more information you want in this regard.