Docker+Fig+Guard

guard

#!/bin/bash

trap "kill 0" SIGINT SIGTERM EXIT

listen -f 0.0.0.0:4000 &
docker exec -it myproject_web_1 bundle exec guard -o 10.0.2.2:4000

Guardfile

guard :rspec, cmd: 'rspec' do

  watch(%r{spec/(.+)_spec.rb$}) { |m| "spec/#{m[1]}_spec.rb" }
  watch(%r{lib/(.+).rb$})     { |m| "spec/lib/#{m[1]}_spec.rb" }
  watch('spec/spec_helper.rb')  { "spec" }

  watch(%r{app/(.+).rb$})                           { |m| "spec/#{m[1]}_spec.rb" }
  watch(%r{app/(.*)(.erb|.haml)$})                 { |m| "spec/#{m[1]}#{m[2]}_spec.rb" }
  watch(%r{app/controllers/(.+)_(controller).rb$})  { |m| ["spec/routing/#{m[1]}_routing_spec.rb", "spec/#{m[2]}s/#{m[1]}_#{m[2]}_spec.rb", "spec/acceptance/#{m[1]}_spec.rb"] }
  watch(%r{spec/support/(.+).rb$})                  { "spec" }
  watch('config/routes.rb')                           { "spec/routing" }
  watch('app/controllers/application_controller.rb')  { "spec/controllers" }

end

I got the host IP figured out (umm, not enough coffee that day I guess).

For newer versions of guard/listen you need to also pass -r on the listen command. And unfortunately in listen 2.10.0 I'm getting an error, which appears to be fixed on guard/listen master.
Here's what I ended up with: https://gist.github.com/thecatwasnot/9dde2e100ccad19660cf
Ubuntu 14.04 -> Vagrant(CoreOS) -> docker