class ApplicationController < ActionController::Base
session[:request_ip] = request.remote_ip
rest of your ApplicationController code
Then read back the value from session[:request_ip] as needed.
The requester’s IP may change from request to request, if they have
IP’s assigned dynamically, for example. Not quite clear how this would
be a “short term debugging requirement”. Also may require browser has
“cookies enabled”, depending on what you’re up to.