Middleware Content Proxy

content_proxy.rb

class ContentProxy
  def initialize(app)
    @app = app
  end
  
  def should_use_cms?
    # Some logic goes here, examining the request path and making the determination
    # about whether to render using the CMS engine or let the request bubble up
    # to the Rails app. This example looks for URIs starting with "/blog"
    env['REQUEST_URI'] =~ /^\/blog/
  end
  
  def cms_path_for_request
    # Some logic goes here, translating the request path to the CMS path. If I want
    # to let the URI "my-rails-server.com/blog/posts" to display content from 
    # "my-content-server.com/posts", then I would use something like this:
    env['REQUEST_URI'] = env['REQUEST_URI'].gsub(/^\/blog/, '/')
  end
  
  def call(env)
    response = Rack::Response.new
    
    # Instead of being the middle-man for POST and admin operations, we'll just redirect
    # admins to the actual CMS site. This catches /cms/ghost as well as /ghost
    if env['REQUEST_URI'] =~ /^(\/cms)?\/ghost/
      response.redirect('https://my-content-server.com/ghost')
      return response.finish
    end

    # Special case for CSS files (which otherwise will not transfer correctly)
    if env['REQUEST_URI'] =~ /\.css/
      response.headers["Content-Type"] = "text/css"
    end
    
    if should_use_cms?
      content_path = cms_path_for_request
      uri = URI.join("https://my-content-server.com", content_path)
      
      # This is the main part of the solution - we're grabbing a full HTTP response from the CMS server,
      # and responding to our users' requests with it. We're also passing status codes like 200 or 404 
      # through, so if we happen to get a page-not-found, we don't respond with an error body and a 200 (OK) status.
      content = HTTParty.get(uri)
      response.status = content.code
      response.body = [content.body]
      
      response.finish
    else
      status, headers, response = @app.call(env)
    end
  end
end

This is an edited / streamlined version of code I'm writing for a production app. I haven't run this in a Ruby interpreter so I can't guarantee it's typo-free, but this is the gist of how we're handling the problem of presenting CMS content as if it's part of our Rails app.