This document provides steps for writing library cookbooks in Chef, including writing custom resources. It recommends: 1. Disregarding dogma like "unit tests first" and instead starting by making things up and working backwards. 2. Creating a cookbook skeleton and embedding a test cookbook to validate the resource. 3. Iterating by implementing the resource, adding tests and specs, and refactoring with confidence as the resource is developed. It also provides tips for writing custom resources, such as being explicit, using markers for negative actions, leveraging load_current_value and converge_if_changed, and avoiding leaky abstractions by keeping resources minimal and splitting them as more

1. Hand Crafted Artisanal
Chef Resources

2. Config Management Camp
Ghent, Belgium
February 2016

3. Sean OMeara
sean@chef.io
@someara

4. whoami

5. Part 1

6. Writing library cookbooks
An opinionated workflow
Step by step

7. Step 1 - Disregard dogma
“Unit tests first” is a dirty lie
https://flic.kr/p/aTSiXF

8. Step 2 - Make things up
Then work backwards
https://flic.kr/p/dXkQ5s

9. Contrived examples are the best
examples

11. Place this off to the side, we will
come back for it later.

12. Step 3 - Create a cookbook
By hand. Be a wizard.
https://flic.kr/p/3mMW6e

13. mkdir -p ~/src/custom-resources-tutorial
cd ~/src/custom-resources-tutorial
emacs metadata.rb

15. Step 4 - Embed a test cookbook.
By hand. Be a wizard. Again.
https://flic.kr/p/ai36NG

16. mkdir -p test/cookbooks/my_file_test
cd test/cookbooks/my_file_test
echo “test cookbook” > README.md
mkdir recipes
touch recipes/default.rb
emacs metadata.rb

18. Step 5 - Tell Berkshelf about it
https://flic.kr/p/k5jmja

19. cd ~/src/custom-resources-tutorial
emacs Berksfile

21. Step 6 - Configure Test Kitchen
https://flic.kr/p/r38F5c

22. emacs .kitchen.yml

24. kitchen test ; echo $?

25. Step 7 - Save game
https://flic.kr/p/6ZJ4G7

26. cd ~/src/custom-resources-tutorial
cp ~/src/chef-cookbooks/docker/.gitignore .
cp ~/src/chef-cookbooks/docker/.rubocop.yml .

27. rubocop -a
git init
git add .
git commit -a -m 'v0.0.1 - cookbook skeleton'
git tag v0.0.1

28. Step 8 - Use resource in test recipe
https://flic.kr/p/8MuUAX

29. emacs test/cookbooks/my_file_test/recipes/
default.rb

31. kitchen converge ; echo $?

32. Step 9 - Implement resource
https://flic.kr/p/bkVKRb

33. cd ~/src/custom-resources-tutorial
mkdir libraries
emacs libraries/my_file.rb

35. kitchen converge ; echo $?
kitchen converge ; echo $?

36. Step 10 - Test for behavior
https://i.ytimg.com/vi/1y8Rqvz-Jcg/
maxresdefault.jpgz

37. mkdir -p test/integration/my_file/inspec
emacs -p test/integration/my_file/inspec/
run_spec.rb

39. kitchen verify ; echo $?

40. Step 11 - Add specs and commit
https://flic.kr/p/rrgfZh

41. cd ~/src/custom-resources-tutorial
mkdir spec
emacs spec/spec_helper.rb

43. emacs spec/my_file_spec.rb

45. rubocop -a
rspec ; echo $?
git add .
git commit -a -m “v0.1.0 - my_file resource”
git tag v0.1.0

46. stove 0.1.0

47. Step 12 - Iterate indefinitely
https://flic.kr/p/8Ny8Jt

48. Congratulations, you have now written one
software.

49. You must now maintain it forever.

50. muahaha.

52. Part 2

53. Custom Resources
Tips and Tricks

54. Be explicit
https://flic.kr/p/pz1JAo

59. Converge twice during development
Use markers for “negative” actions
https://flic.kr/p/pqwd5U

62. Tests let you refactor with confidence
https://flic.kr/p/4WnjM4

64. STAR WIPE

66. Pure Ruby resources
https://flic.kr/p/5km2fM

67. Pure Ruby resources utilize
- The Ruby Standard Library
- Chef helper libs (mixlib-shellout)
- Ruby gems

69. It might make sense to vendor gems

70. load_current_value
- Runs at converge time
- Just before the action body
- Loads desired state values

72. converge_if_changed
- Runs if any desired_state: true
property differs from user input
- desired_state: false avoids
comparison

74. coerce transforms values
- Called when property is set
- Called when property is read
- Use this to raise errors on bad input

75. The docker_container resource uses
coercion heavily
https://github.com/chef-cookbooks/
docker/blob/master/libraries/
docker_container.rb

76. lazy defaults
- Delays evaluation until used
- Useful for calculated values

78. Composite resources
https://flic.kr/p/fm58oo

79. Composite resources
- Reuse Chef resources
- Actions look like recipes
- Do not use load_current_value

80. etcd_installation_binary :create

81. httpd_config_rhel :create

82. Avoid leaky abstractions
https://flic.kr/p/7d1kDc

83. Resources should be minimalist

84. Early versions might be simple

86. They rarely stay that way

87. Iterate and add more features
Break down into smaller resources

88. Use naming semantics to
describe strategy

89. etcd_installation_binary
etcd_installation_docker
etcd_installation_package
etcd_service_manager_docker
etcd_service_manager_execute
etcd_service_manager_systemd
etcd_service_manager_sysvinit
etcd_service_manager_upstart

90. Recycle patterns as they emerge

91. docker_installation_binary
docker_installation_package
docker_installation_script
docker_service_manager_execute
docker_service_manager_systemd
docker_service_manager_sysvinit
docker_service_manager_upstart

92. Chef selects defaults with the
provider resolution system

93. …

94. …

95. Compose resources
Most specific to least specific

97. Enjoy

98. fin