Remote Debugging with Foreman and Byebug

With Rails 7 recently dropping there are a few improvements outside of the great new features that might take new projects by surprise. The first that I encountered after starting up a new Rails project was the bin/dev script that now uses foreman by default.

The benefit of foreman is you can create a Procfile that defines all the processes your application will need to run. Processes like a web app process and maybe a background worker process and foreman will run them both from a single command, foreman start. Then you can reuse this Procfile in production namely with Heroku that will create processes for all that are listed within that file. The downside is that all those processes are wrapped up in a single tab in your command line and doesn't lend itself well to debugging. This is because it is taking the output from all the processes defined and is simply echoing their output to you. When you debug you need access to the underlying process in order to interact with the debugger. You can get around this by running the web process in a separate tab but that takes away the benefit of foreman. Luckily, byebug has a solution with remote debugging!

Remote debugging with byebug is really simple to set up. Simply create a config/initializers/byebug.rb and start the server.

# config/initializers/byebug.rb
# frozen_string_literal: true

if Rails.env.development?
  require 'byebug/core'
    Byebug.start_server 'localhost', ENV.fetch('BYEBUG_SERVER_PORT', 8989).to_i
  rescue Errno::EADDRINUSE
    Rails.logger.debug 'Byebug server already running'

A few things to highlight:

  • The if Rails.env.development? is to ensure we start the server only in the development environment and not in the test environment. This makes it easier to debug in test because you're running those commands in a single command line process instead of through foreman but in development you're probably running it with foreman.
  • The begin rescue block is to allow multiple runs the rails command. I ran into an issue where I had the development server running but wanted to generate a migration using rails g migration. That command runs the initializers and was throwing an error since the byebug server was already up and running on the other process. In that case we just ignore it and output the error to the logs.
  • The default port for the byebug server can be whatever you want and can be set via the BYEBUG_SERVER_PORT environment variable. I've set the default port to be 8989 but it can be whatever you want that is not in use.

Once all that is in place you can open another command line prompt and run byebug -R localhost:8989. Then once your web process hits the byebug command and stops for debugging the new process will have access to it and you can debug to your heart's content.

The default debugger in Rails 7 is now the default Ruby debugger aptly named debugger. There are some docs that say debugger supports remote debugging but I wasn't able to ever get it to work within foreman.

I hope this makes using foreman and debugging in Rails a more comfortable and happy experience!