How Does Bundler Work, Anyway? (RailsConf 2015)

We all use Bundler at some point, and most of us use it every day. But what does it do, exactly? Why do we have to use bundle exec? What's the point of checking in the Gemfile.lock? Why can't we just `gem install` the gems we need? Join me for a walk through the reasons that Bundler exists, and a guide to what actually happens when you use it.

Transcript

1. how does bundler work, anyway?
2. how does bundler work, anyway?
3. a brief (?) history of dependency management
4. André Arko @indirect
8. let’s share ruby code
9. Gemfile gem “foo”
10. Terminal $ bundle install
11. Terminal $ bundle exec foo
12. done! pretty cool, right?
13. but… what just happened?
14. iiiiit’s History ⚔ Time
15. 1994 2000 2003 2009 dependency timeline require setup.rb RubyGems Bundler
16. require it loads the codes
17. def require(filename) eval File.read(filename) end
18. i’m sure it’s fine run code twice?
19. $LOADED_FEATURES = [] def require(filename) if $LOADED_FEATURES.include?(filename) return true end eval File.read(filename) $LOADED_FEATURES << filename end
20. probably fine too only absolute paths?
21. $LOAD_PATH = [] def require(filename) full_path = $LOAD_PATH.first do |path| File.exist?(File.join(path, filename)) end eval File.read(full_path) end
22. load paths are ⛄ pretty ❄ cool
23. but now we need… setup.rb
24. how do setup.rb? ruby setup.rb setup ruby setup.rb config ruby setup.rb install
25. use ruby libraries 1. Find a cool library 2. Download the library 3. Untar the library 4. Run `ruby setup.rb all`
26. no versions no uninstall but it’s fine, I’m sure
27. maybe a little bit incredibly tedious
28. what if you could… gem install gem uninstall gem list rails
29. bonus round! gem install rails -v 4.1 gem install rails -v 4.2 gem install rails -v 5.0
30. gem "rack", "1.0" require "rack"
31. $ rackup _1.2.2_ -p 3000
32. so many gems! 100,000 gems 1,000,000 versions
33. but gem apps don’t play well with others
34. welcome to the team here’s your machine we expect setting up to take a week
35. # config/application.rb […] config.gem “rack” config.gem “rails” config.gem “what?” […]
36. “why is this broken in production?” “dunno, it works on every developer machine” 3 days of debugging later… “oh, look, one production server has frobnitz 1.1.3, but the others have 1.1.4” “welp. that explains those exceptions ”
37. version conflicts gem install rails rails s cd ../other-project rails s
38. activation errors how common can they be, really?
39. $ rails s Gem::LoadError: can't activate rack (~> 1.0.0., runtime) for ["actionpack-2.3.5"], already activated rack-1.1.0 for ["thin-1.2.7"] activation errors
40. the moral runtime resolution install-time resolution
41. wait… how do we resolve at install-time?
43. addressable (2.3.7) arel (6.0.0) bcrypt (3.1.10) binding_of_caller (0.7.2) debug_inspector (>= 0.0.1) builder (3.2.2) byebug (3.5.1) columnize (~> 0.8) debugger-linecache (~> 1.2) slop (~> 3.6) celluloid (0.16.0) Gemfile.lock
44. bundle install my old friend 1. Read the Gemfile (and lock, if it's there) 2. Ask RubyGems.org for a list of every gem we need 2. Find gems allowed by the Gemfile that work together 3. Write down those versions in the lock for future installs 4. Install gems until every locked gem is installed
45. bundle exec everyone’s nemesis 1. Read the Gemfile (and lock, if it's there) 2a. Use locked gems if possible OR 2b. Find versions that work to put in the lock 3. Remove any existing gems the $LOAD_PATH 4. Add each gem in the lock to the $LOAD_PATH
46. pro tip no more bundle exec! $ bundle binstubs rspec-core $ bin/rspec repeat as needed for other gems
47. was that the end? in a word, no.
48. I want YOU to contribute 2 @bundlerio team@bundler.io
49. or if you’re too busy, fund this work. http://rubytogether.org/join