Pros and Cons of using API instead of direct DB Access

Question

I found myself in several discussions throughout the week regarding a web application under development and whether it should leverage an API that is being created.

Here's the situation. I have a PHP MVC web application with a MySQL DB as well as several mobile apps all being developed in house. For the mobile apps we're building a rest api. The big question is why should my PHP web application now use that rest api? I've always expected the use of an API to be for third party systems that need to interface with my database or for systems built on a different technology. The web app is certainly not a third party system and the services are in PHP. If the API is on a different server than the web app then I guess it could be considered a third party system... which has not been decided yet.

To me, it just seems strange to leverage the API for the web app especially since the APIs services are going to be limited to about 50% of the functions available in the web app leaving me to build the other 50% that would be unique to the web app. I also foresee a performance hit to the web app stepping through the service layer rather than just accessing the DB directly. On the other side I see more maintenance having a code base for my web app hitting the DB and similar functions built into the api for mobile apps.

Has anyone found themselves in a similar situation and can provide some technical pros and cons to why I should just use the API or can point me to a solid case study?

Answer 1

Pros:

• What if one day you decide to move the backend app to another machine? With an API, your app code won't need to change.
• What if one day you grow, and need to scale to 10000 backend apps instead of 1? With an API, your app code won't need to change.
• What if one day you decide to swap out MySQL for Mongo? With an API, your app code won't need to change.
• ^ Enforced separation of concerns between data access layer (DB) and application

Cons:

• More code up front when writing the app layer
• More incremental work when you need to support a new app layer feature that your API doesn't support yet

To me, the pros clearly win.