#Heroku, Ruby on Rails and PhantomJS
In this post, I’m going to show you how to modify an existing Ruby on Rails app running on Heroku’s Cedar stack to use PhantomJS for screen scraping. If you’ve never heard of PhantomJS, it’s a command-line WebKit-based browser (that supports JavaScript, cookies, etc.).
Let’s get started. This is a high-level overview of the required steps:
- Modify your app to use multiple Heroku buildpacks.
- Extend your app to use both the Ruby as well as the PhantomJS buildpacks.
- Confirm that everything worked.
David Dollar has created Heroku buildpack that allows you to use multiple Heroku buildpacks for your app. ;-) Install it by setting an environment variable:
$ heroku config:set BUILDPACK_URL=https://github.com/ddollar/heroku-buildpack-multi.git
Extend your app to use both the Ruby as well as the PhantomJS buildpacks
Create a .buildpacks
file in the root directory of your app:
$ touch .buildpacks
Within your .buildpacks file, specify that your app uses both the Ruby and the PhantomJS buildpacks. This prevents you from having to (cross-)compile PhantomJS yourself. Make the contents of your .buildpacks file:
https://github.com/heroku/heroku-buildpack-ruby
https://github.com/stomita/heroku-buildpack-phantomjs
PhantonJS has a dependency on libQtWebKit.so.4, which the PhantomJS buildpack installs on Heroku in/app/vendor/phantomjs/lib. Modify your Heroku app’s LD_LIBRARY_PATH to include this directory:
$ heroku config:set PATH="/usr/local/bin:/usr/bin:/bin:/app/vendor/phantomjs/bin"
$ heroku config:set LD_LIBRARY_PATH=/usr/local/lib:/usr/lib:/lib:/app/vendor/phantomjs/lib
Confirm that everything worked
First things first - load your app in your web browser and confirm that it still comes up. :-) Next, launch a Heroku bash shell:
$ heroku run bash
Within the bash shell, invoke the PhantomJS executable to ensure that it runs:
$ vendor/phantomjs/bin/phantomjs —version
Good to go! Now you’re ready to call PhantomJS from your Ruby code.
Apologies in advance if this is way out of scope, but after following these directions successfully, I'm still unclear on how I'd actually execute Phantomjs commands within a Rails controller on Heroku. I've spent hours googling and on Stack Overflow to no avail but feel I'm missing something obvious.
How do I reference phantomjs from within my Rails app and then use Rails to execute Phantomjs commands? Thank you!!