Is it good practice for a website to use its own API?

Question

Is it good practice to develop the API while developing the site so the site itself actually uses the API? Or is there a performance hit if choosing to do this?

For example, does anyone know if mature sites such as Facebook or Digg use their own API to CRUD (Create, Read, Update, Delete) or do they have their own backend? Thanks

Answer 1

I doubt Facebook and such use their own API. There are a couple of reasons not to use your own API for the site itself:

1. You can make data access more performant by using the database directly instead of doing extra requests and (de)serialization.
2. Probably easier to implement efficient caching with memcached etc
3. Importantly, you won't have to conform to your public API when extending your site (you don't want to change your public API very often, that'll just annoy everyone)

Answer 2

I do think it's a good idea to have a low-level interface to the application that you can use without a browser per se, and that the site should use that interface to do its stuff.

That interface doesn't have to be the API itself, it could be a layer that's lower in level than the API, and that is used by both the API and the production website.

It's generally a bad idea if the API just duplicates the website.

i.e., the following is bad

# hypothetical example of bad duplication

def website_update_blog_post(request):
    user = request.username()
    ensure_logged_in(user)
    post = Posts.objects.upsert(request.post_title, request.post_body)
    trigger_notifications(post)

.....

def api_update_blog_post(user, password, title, body):
    verify_login(user, password)
    post = Posts.objects.upsert(title, body)
    trigger_notifications(post)