difference between Umbraco Surface controller and API controller

What is the difference between Surface and API controller for Umbraco?

In standard MVC the general rule is:

API is used for returning data, that can be consumed by multiple applications.
Controller is used for returning views

But I am bit unsure with Umbraco.

So far I have been using surface controller to post data from and into forms, which makes me wonder if I am using it correctly and if should I use instead API controller for this

What are your reasons for your opinion?

Solution

I don't think that you are mistaken. Umbraco Surface Controllers deal with front-end user interactions like posting data into forms (from http://our.umbraco.org/documentation/Reference/Mvc/surface-controllers)

A SurfaceController is an MVC controller that interacts with the front-end rendering of an UmbracoPage. They can be used for rendering Child Action content, for handling form data submissions and for rendering Child Action macros. SurfaceControllers are auto-routed meaning that you don't have to add/create your own routes for these controllers to work.

Whereas you'd use API controllers to access data in other domains, or the back-end of your current site.

There is a possibility that Umbraco will start to be more commonly used purely through its own API (using ContentService for example) and that the /umbraco/ access to the back office will become unused in more sophisticated implementations at which stage web apis will be used by controllers to connect models & views. Disconnecting umbraco from its website is a more grown-up model for a CMS and could cure many deployment issues so that nagging feeling that you should be using web api in more use cases could very well be a good one.