tl;dr – the source is here

Here’s how I mount a Grape API on Rack and also serve static pages. Most useful for building a service with documentation.

Setup bundler with the required gems. I am using the next version of Grape (frontier branch and the next version of rack-contrib which contains Rack::TryStatic that we’re going to want to use).

Static content goes to a new public folder, for example public/index.html.

Our application will need to boot with all these gems, we’ll do it Rails-style by starting with a config/boot.rb file. It brings in Bundler.

Lets define our Acme Grape API that will have a system resource that answers ping requests with “pong”. This goes into api/api.rb.

The application requires Bundler, all the gems in Gemfile and our API. Lets define it in config/application.rb.

Note the odd File.expand_path construct, borrowed from Rails, - it translates a relative path to the current file into an absolute path, there’re allowing us to run the application from any directory – useful for hosting where you never know who boots the application.

Continuing to borrow from Rails, we will want different environments (development, production, etc.), so it’s a good idea to keep things organized. Setup the environment in config/environment.rb and then load the application.

Finally, we need to “rackup” this whole thing in config.ru. We will use Rack::TryStatic to serve static pages when available and pass through to the Acme API otherwise.

Run the application with bundle exec rackup.

Full source on Github.