Debugging ManageIQ with Remote Pry

Interactive debugging using pry or byebug is normally difficult with ManageIQ, as rake evm:start launches the server and worker processes in the background. Therefore the only way to do interactive debugging is with pry-remote or byebug running in remote mode.

Running ManageIQ with byebug was exceedingly slow, so this guide will focus on remote debugging using pry.

Adding dependencies

You’ll need to add the following gems to your dev overrides file in bundler.d/:

  gem 'pry'
  gem 'pry-remote'
  gem 'pry-nav'

Starting the debugger

Setting a breakpoint with pry requires adding the following line somewhere in your code:

#code executes until this line
binding.remote_pry
#code here does not execute

When execution reaches the remote_pry call, the line pry-remote] Waiting for client on drb://localhost:9876 will print to STDOUT (stderr?) and execution will block until you connect the client debug process.

To connect the debugger, simply run from the ManageIQ root dir:

bundle exec pry-remote

which will attempt to connect to the pry server on port 9876.

With the addition of pry-nav, you’ll have access to commands continue, step, and next, to navigate through your code.

Notes

Setting breakpoints from within pry is currently not possible with pry-nav. As a workaround, it’s possible to set conditional breakpoints throughout your code like so:

binding.remote_pry

# do some stuff

if @breakpoint_enabled
  binding.remote_pry
end

And simply set @breakpoint_enabled = true when you reach your first breakpoint to enable the next breakpoint to trigger.

Note that you will have to continue to exit out of pry and then bundle exec pry-remote again to enter into subsequent breakpoints in the same process.