Q:

run selenium with chrome driver on heroku: `cannot find Chrome binary`

I'm a noob as it comes to linux setup (and heroku), so apologies if this question is basic.
I want to run selenium webkit (in ruby) on Heroku. I face a difficulty that my script cannot find Chrome binary file.
I actually got chrome to work by itself:
~ $ chromedriver
Starting ChromeDriver 2.22.397932 (282ed7cf89cf0053b6542e0d0f039d4123bbb6ad) on port 9515
Only local connections are allowed.

chromedriver being a file that I copied from /app/vendor/bundle/bin/chromedriver, just to make it easier for now. chromedriver file there exists because I installed chromedriver-helper gem. The gem was supposed to make the binary file available for ruby processes but didn't.
I've also tried setting path explicitly, e.g. Selenium::WebDriver::Chrome.driver_path = 'chromedriver' in my ruby code, with the aforementioned file located in the root category.
It all works perfectly locally (with or without the driver_path)
What can be the cause? I've read this SO thread from years ago, but it seems outdated to me. Any ideas would be greatly appreciated!
error trace:
~ $ ruby bin/run.rb
/app/vendor/bundle/ruby/2.2.0/gems/selenium-webdriver-2.53.4/lib/selenium/webdriver/remote/response.rb:70:in `assert_ok': unknown error: cannot find Chrome binary (Selenium::WebDriver::Error::UnknownError)
  (Driver info: chromedriver=2.22.397932 (282ed7cf89cf0053b6542e0d0f039d4123bbb6ad),platform=Linux 3.13.0-91-generic x86_64)
    from /app/vendor/bundle/ruby/2.2.0/gems/selenium-webdriver-2.53.4/lib/selenium/webdriver/remote/response.rb:34:in `initialize'
    from /app/vendor/bundle/ruby/2.2.0/gems/selenium-webdriver-2.53.4/lib/selenium/webdriver/remote/http/common.rb:78:in `new'
    from /app/vendor/bundle/ruby/2.2.0/gems/selenium-webdriver-2.53.4/lib/selenium/webdriver/remote/http/common.rb:78:in `create_response'
    from /app/vendor/bundle/ruby/2.2.0/gems/selenium-webdriver-2.53.4/lib/selenium/webdriver/remote/http/default.rb:90:in `request'
    from /app/vendor/bundle/ruby/2.2.0/gems/selenium-webdriver-2.53.4/lib/selenium/webdriver/remote/http/common.rb:59:in `call'
    from /app/vendor/bundle/ruby/2.2.0/gems/selenium-webdriver-2.53.4/lib/selenium/webdriver/remote/bridge.rb:649:in `raw_execute'
    from /app/vendor/bundle/ruby/2.2.0/gems/selenium-webdriver-2.53.4/lib/selenium/webdriver/remote/bridge.rb:123:in `create_session'
    from /app/vendor/bundle/ruby/2.2.0/gems/selenium-webdriver-2.53.4/lib/selenium/webdriver/remote/bridge.rb:87:in `initialize'
    from /app/vendor/bundle/ruby/2.2.0/gems/selenium-webdriver-2.53.4/lib/selenium/webdriver/chrome/bridge.rb:48:in `initialize'
    from /app/vendor/bundle/ruby/2.2.0/gems/selenium-webdriver-2.53.4/lib/selenium/webdriver/common/driver.rb:64:in `new'
    from /app/vendor/bundle/ruby/2.2.0/gems/selenium-webdriver-2.53.4/lib/selenium/webdriver/common/driver.rb:64:in `for'
    from /app/vendor/bundle/ruby/2.2.0/gems/selenium-webdriver-2.53.4/lib/selenium/webdriver.rb:84:in `for'
    from /app/lib/mealpass_orderer.rb:12:in `initialize'
    from /app/lib/mealpass_orderer.rb:8:in `new'
    from /app/lib/mealpass_orderer.rb:8:in `run'
    from bin/run.rb:3:in `<main>'

UPDATE:
I tried the same with AWS EC2 server (launched instance, cloned git repo, installed all dependencies). The same happens there as well. That is, able to execute chromedriver from terminal, but seeing same error when run the script.

A:

ChromeDriver is just a driver for Chrome. It needs the actual Chrome browser installed on the same machine to actually work.
Heroku doesn't have Chrome installed on its dynos by default. You need to use a buildpack that installs Chrome. For example:
https://github.com/dwayhs/heroku-buildpack-chrome
You can see how it fetches Chrome:
https://github.com/dwayhs/heroku-buildpack-chrome/blob/master/bin/compile#L36-38

