Prerender Rails Embedded

A rails gem to use prerender_rails middleware to render JavaScript web app calling phantomjs on the fly without installing other services.

Overview

With Prerender Rails Embedded can be avoided a new node.js server installation in a rails environment because rails will launch a phantomjs binary to render the js page.

Just to try out the prerender.io/server technology and for low traffic situation, this plugin is not meant to support heavy traffic loads.

Installation

Add in your Gemfile a line with

    gem 'prerender_rails_embedded'

and launch a

bundle install

to install it. Then in the config/environment/production.rb it should be added:

    config.middleware.use Rack::Prerender before_render: PrerenderRailsEmbedded.local_renderer

Test

To test the correct functioning of the prerender_rails_embedded gem just start rails with rails s and launch a curl to a (js generated) url like this:

curl -H "User-Agent: Mozilla/5.0 baiduspider" \
    "http://localhost:3000/articles/a0af82a84-d386-4690-9f68-81ac768bc6d3"

It should show a completely rendered page in standard output.

Warning

WEBrick and Thin don't support multiple nested requests so, using them it will hang the request until a timeout is issued by the web server. To test it out you should consider using unicorn with more than one worker thread.

Just add gen unicorn to your Gemfile launch bundle install create a config/unicorn.rb file with content (adjusting it to your needs)

    # config/unicorn.rb
    worker_processes 3
    timeout 30
    preload_app true

    before_fork do |server, worker|

      Signal.trap 'TERM' do
        puts 'Unicorn master intercepting TERM and sending myself QUIT instead'
        Process.kill 'QUIT', Process.pid
      end

      defined?(ActiveRecord::Base) and
        ActiveRecord::Base.connection.disconnect!
    end

    after_fork do |server, worker|

      Signal.trap 'TERM' do
        puts 'Unicorn worker intercepting TERM and doing nothing. Wait for master to sent QUIT'
      end

      defined?(ActiveRecord::Base) and
        ActiveRecord::Base.establish_connection
    end

and launch the web server with the command:

    bundle exec unicorn -p 3000 -c ./config/unicorn.rb

To test the actual invokation

$ curl -H 'User-Agent: baiduspider' https://dev.etalia.net/articles/a6c37930c-a3df-482d-b9e5-b4333473e1ae

TODOs

This has been a very quick development so there are

• exceptions should exit immediately from phantomjs and in some cases they DON'T
• add a timeout for too long phantojs processing
• support 404 and error code in the same way prerender.io (server) does

Future enhancements

• add memory/disk cache deciding a correct eviction policy to avoid rendering pages multiple times.