good practice: REST API as the interface between the interface layer and business layer?

Question

I was thinking about the architecture of a web application that I am planning on building and I found myself thinking a lot about a core part of the application. Since I will want to create, for example, an android application to access it, I was already thinking about having an API.

Given the fact that I will want to have an external API to my application from day one, is it a good idea to use that API as an interface between the interface layer (web) and the business layer of my application? This means that even the main interface of my application would access the data through the API. What are the downsides of this approach? performance?

In more general terms, if one is building a web application that is likely to need to be accessed in different ways, is it a good architectural design to have an API (web service) as the interface between the interface layer and business layer? Is REST a good "tool" for that?

Answer 1

Sounds like you've got two questions there, so my answer is in two parts.

Firstly, should you use an API between the interface layer and the business layer? This is certainly a valid approach, one that I'm using in my current project, but you'll have to decide on the benefits yourself, because only you know your project. Possibly the largest factor to consider is whether there will be enough different clients accessing the business layer to justify the extra development effort in developing an API? Often that simply means more than 1 client, as the benefits of having an API will be evident when you come to release changes or bug fixes. Also consider the added complexity, the extra code maintenance overhead and any benefits that might come from separating the interface and business layers such as increased testability.

Secondly, if you implement an API, should you use REST? REST is an architecture, which says as much about how the remainder of your application is developed as it does the API. It's no good defining resources at the API level that don't translate to the Business Layer. Rest tends to be a good approach when you want lots of people to be able to develop against your API (like NetFlix for example). In the case of my current project, we've gone for XML over HTTP, because we don't need the benefits that Rest generally offers (or SOAP for that matter).

In general, the rule of thumb is to implement the simplest solution that works, and without coding yourself into a corner, develop for today's requirements, not tomorrow's.

Chris