Why does my headless browser script open Firefox, causing issues in a cron job?

Other Questions Headless Browser
1

I created a script intended for execution via a cron job, using a headless browser approach. I utilized the Headless gem, aiming for it to operate without a graphical display. However, upon running the script, Firefox still launches, which seems counterproductive to the concept of headless operation. I expected it to function similarly to PhantomJS, executing in the background without display access. Am I misunderstanding the functionality of this gem? Also, when I previously tried using PhantomJS, it timed out when attempting to access the email input field on a Google login page. Below is my script example:

#coding: utf-8
require 'watir-webdriver'
require 'headless'

# Start headless session
headless = Headless.new
browser = Watir::Browser.start 'http://app.example.com/admin'
# Perform login steps here

# Fetch yesterday's data
# Close browser after data retrieval
browser.close
headless.destroy

# Log timestamp
current_time = Time.now
puts "Data retrieved at: " + current_time.inspect
"

When I execute the script outside of the cron environment, it functions correctly, but it fails while being run by cron. Any advice would be appreciated!

2

It seems like the core of your issue lies with the way your script interacts with the headless environment when being executed in a cron job. Let’s break down the problem and address it step-by-step. Here are the points you should consider and modifications you can make to your script to ensure it works correctly with cron and in a headless manner:

  1. Initialization of Headless Session: Ensure you initialize and start the headless session properly using the begin and end block to make sure it is correctly managed.

  2. Providing Display Number: When setting up a headless session, explicitly provide a display number which can sometimes avoid conflicts.

  3. Running Cron with a Full Path: Ensure your cron job uses the full path to the ruby executable and the script to avoid environment-specific issues.

  4. Logging Errors for Debugging: Add error handling and logging to understand where it might be failing when executed via cron.

Here’s an updated version of your script to incorporate these suggestions:

#coding: utf-8
require 'watir-webdriver'
require 'headless'

begin
  # Start headless session
  headless = Headless.new(display: 99)
  headless.start

  # Start browser session with headless
  browser = Watir::Browser.start 'http://app.example.com/admin'
  # Perform login steps here

  # Fetch yesterday's data
  # Close browser after data retrieval
  browser.close
rescue Exception => e
  # Log an error message with timestamp
  File.open('/path/to/your/logfile.log', 'a') do |f|
    f.puts "Error at: #{Time.now} - #{e.message}"
  end
ensure
  headless.destroy if headless
end

# Log timestamp of data retrieval
current_time = Time.now
puts "Data retrieved at: " + current_time.inspect

Additional Tips:

  • Make your script executable by adding the shebang at the top: #!/usr/bin/env ruby
  • In your crontab file, ensure you have something like:
    * * * * * /usr/bin/ruby /path/to/your_script.rb >> /path/to/your_output.log 2>&1
  • Check environment variables since cron runs with a limited environment compared to your user session.
  • Look into cron output or log files (/var/log/syslog or /var/log/cron) for potential errors.

By making these adjustments, your script should execute in a fully headless manner within the cron job environment.