Europe PMC Tech BlogRemote debug Ruby on Rails running in a Docker container using RubyMine
RubyMine brings a sophisticated debugger with a graphical UI for Ruby, JS, and CoffeeScript. You can set breakpoints and run your code step by step with all the information at your fingertips, without having to modify your code as Pry.
This article is written about how one can use RubyMine to remote debug a Ruby on Rails application that even runs inside a Docker container.
Versions of software in our environment
- RubyMine 2017.2.4 (Build #RM-172.4155.44, built on September 26, 2017)
- Ruby inside docker (ruby 2.4.2p198 (2017-09-14 revision 59899) [x86_64-linux])
- Ruby SDK and Gems used by RubyMine (ruby-2.4.2-p198)
Note: for Ruby SDK used by RubyMine, we are just using a local Ruby interpreter /usr/bin/ruby, not a remote one. (See below)
Below are the detailed steps as a demo
1. Start the docker container
docker run --name rails-demo -p 1234:1234 -p 3080:3000 -it ruby bash
2. Steps inside the docker container
Be sure you have the following gems in your Gemfile, and better to comment out gem pry-byebug if it’s there, to avoid possible interference.
## gem 'pry-byebug'
gem 'debase', '0.2.2.beta10'
gem 'ruby-debug-ide'
Update the dependencies of your application if necessary
bundle install
Start your rails server
/home/hello_rails## rdebug-ide --host 0.0.0.0 --port 1234 --dispatcher-port 26162 -- bin/rails s
3. Remote debug from RubyMine
Now start RubyMine, Run -> Debug… -> Edit Configurations…
Click plus sign ‘+’ to add new configuration, and choose Ruby remote debug.
Fill the form as shown above and click the Debug button. Now you’ll see in the docker container the Rails server gets started:
/home/hello_rails## rdebug-ide --host 0.0.0.0 --port 1234 --dispatcher-port 26162 -- bin/rails s
Fast Debugger (ruby-debug-ide 0.6.0, debase 0.2.2.beta10, file filtering is supported) listens on 0.0.0.0:1234
=> Booting Puma
=> Rails 5.1.4 application starting in development
=> Run `rails server -h` for more startup options
Puma starting in single mode...
* Version 3.10.0 (ruby 2.4.2-p198), codename: Russell's Teapot
* Min threads: 5, max threads: 5
* Environment: development
* Listening on tcp://0.0.0.0:3000
Use Ctrl-C to stop
Now, you can set breakpoints in RubyMine, and start remote debugging it :-)
Go to browser with URL: http://localhost:3080/say/hi (Note port 3080 is mapped from 3000, see above the command of starting the docker container)
The breakpoint is hit as shown below, where you can inspect variables, etc.
One more caveat worth mentioning is that you need to be sure the web server puma starts in single mode. For me the cluster mode does not work for remote debugging, where you’ll have errors like “terminating timed out worker”. For development, single mode should be good enough.