Deploy Slate to Heroku

Documentaton is a big part of a project, more critical if you need to hand off the details of your API to multiple third parties that will interact with it. Here you will lean how to deploy Slate, the API documentation generator based on Middleman, on Heroku, and how to configure it to generate the static HTML files with each commit on a repository.

Table of Contents

Some context

One particular problem we were facing at work, was deploying documentation of our API on Heroku, without the need to host the generated files into our repository. This was leading us to a lot of manipulations and possibly errors, particularly when we wanted someone outside the dev team to write the documentation. What we were trying to achieve was to commit the markdown page and be done with it.

Set up Slate locally

Slate is not a library, nor a Ruby gem, but a fully configured project to ease the redaction of APIs documentation. It take the form of a clonable Github repository. You can modify the files to your needs in the /docs directory, like using your own logo, though it is already coming with a lovable UI theme. Create your markdown files and they will be transformed into a single page HTML file.

$ git clone
# Install middleman and all the dependencies
# /!\ You will probably need to install nodejs as well as it
# is required by one of the dependencies
$ bundle install
# Execute the middleman local server
$ bundle exec middleman
# OR
$ bundle exec middleman build --clean
# To only generate the files without lauching the server

The generated HTML files will be placed in a the /docs directory, based on what’s int the /sources one.

Building the documentation on Heroku

Middleman is a static site generator, so we want to be able to generate the files as we deploy, without to have to commit the entire result in our repository. The only way for Heroku to generate the files on deploy, is to use the assets:precompile asset pipeline, via a Rake task. This was originally used for Rails app, but will come handy for our particular use.

Create a Rakefile at the root of the project and add it the following.

require 'bundler/setup'

namespace :assets do
  task :precompile do
    # Build Slate/Middleman documentation
    sh 'bundle exec middleman build --clean'

Now our documentation will be build every time the code is pushed on Heroku.

Serving files

We will be using a Rack app to serve the HTML files on the server, as it is a relatively painless to implement and configure. Rack must know which files it should serve as static assets, so for that, we will need to create a file.

use Rack::Static,
    :urls => ['/docs'],
    :root => 'docs',
    :index => 'index.html'

run lambda { |env|
      'Content-Type'  => 'text/html',
      'Cache-Control' => 'public, max-age=86400'
    },'docs/index.html', File::RDONLY)

You can use the Puma web server to tied all of this together, it’s a performant web server that plays nice whith Rack. Add a Procfile to the project and insert the gem gem 'puma' in the Gemfile.

web: bundle exec puma -p $PORT

Customizing the Middleman build configuration

Middleman source and build directory can be customized to your needs, you will have to edit the configuration file config.rb.

Changing the source files directory:

set :source, "#{File.dirname(__FILE__)}/my_source_dir"

Changing the build directory:

set :build_dir, "#{File.dirname(__FILE__)}/my_build_dir"