Hand Crafted ArtisanalChef Resources

Config Management CampGhent, BelgiumFebruary 2016

Sean OMearasean@chef.io

@someara

whoami

Part 1

Writing library cookbooks An opinionated workflow Step by step

Step 1 - Disregard dogma “Unit tests first” is a dirty lie

https://flic.kr/p/aTSiXF

Step 2 - Make things up Then work backwards

https://flic.kr/p/dXkQ5s

Contrived examples are the best examples

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

Step 3 - Create a cookbook By hand. Be a wizard.

https://flic.kr/p/3mMW6e

mkdir -p ~/src/custom-resources-tutorialcd ~/src/custom-resources-tutorialemacs metadata.rb

Step 4 - Embed a test cookbook. By hand. Be a wizard. Again.

https://flic.kr/p/ai36NG

mkdir -p test/cookbooks/my_file_testcd test/cookbooks/my_file_testecho “test cookbook” > README.mdmkdir recipestouch recipes/default.rbemacs metadata.rb

Step 5 - Tell Berkshelf about it

https://flic.kr/p/k5jmja

cd ~/src/custom-resources-tutorialemacs Berksfile

Step 6 - Configure Test Kitchen

https://flic.kr/p/r38F5c

emacs .kitchen.yml

kitchen test ; echo $?

Step 7 - Save game

https://flic.kr/p/6ZJ4G7

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

rubocop -agit initgit add .git commit -a -m 'v0.0.1 - cookbook skeleton' git tag v0.0.1

Step 8 - Use resource in test recipe

https://flic.kr/p/8MuUAX

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

kitchen converge ; echo $?

Step 9 - Implement resource

https://flic.kr/p/bkVKRb

cd ~/src/custom-resources-tutorialmkdir librariesemacs libraries/my_file.rb

kitchen converge ; echo $?kitchen converge ; echo $?

Step 10 - Test for behavior

https://i.ytimg.com/vi/1y8Rqvz-Jcg/maxresdefault.jpgz

mkdir -p test/integration/my_file/inspecemacs -p test/integration/my_file/inspec/run_spec.rb

kitchen verify ; echo $?

Step 11 - Add specs and commit

https://flic.kr/p/rrgfZh

cd ~/src/custom-resources-tutorialmkdir specemacs spec/spec_helper.rb

emacs spec/my_file_spec.rb

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

stove 0.1.0

Step 12 - Iterate indefinitely

https://flic.kr/p/8Ny8Jt

Congratulations, you have now written one software.

You must now maintain it forever.

muahaha.

Part 2

Custom Resources Tips and Tricks

Be explicit

https://flic.kr/p/pz1JAo

Converge twice during development Use markers for “negative” actions

https://flic.kr/p/pqwd5U

Tests let you refactor with confidence

https://flic.kr/p/4WnjM4

STAR WIPE

Pure Ruby resources

https://flic.kr/p/5km2fM

Pure Ruby resources utilize

- The Ruby Standard Library - Chef helper libs (mixlib-shellout) - Ruby gems

It might make sense to vendor gems

load_current_value

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

converge_if_changed

- Runs if any desired_state: true property differs from user input

- desired_state: false avoids comparison

coerce transforms values

- Called when property is set - Called when property is read - Use this to raise errors on bad input

The docker_container resource uses coercion heavily

https://github.com/chef-cookbooks/docker/blob/master/libraries/docker_container.rb

lazy defaults

- Delays evaluation until used - Useful for calculated values

Composite resources

https://flic.kr/p/fm58oo

Composite resources

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

etcd_installation_binary :create

httpd_config_rhel :create

Avoid leaky abstractions

https://flic.kr/p/7d1kDc

Resources should be minimalist

Early versions might be simple

They rarely stay that way

Iterate and add more features Break down into smaller resources

Use naming semantics to describe strategy

etcd_installation_binaryetcd_installation_dockeretcd_installation_package

etcd_service_manager_dockeretcd_service_manager_executeetcd_service_manager_systemdetcd_service_manager_sysvinitetcd_service_manager_upstart

Recycle patterns as they emerge

docker_installation_binarydocker_installation_packagedocker_installation_script

docker_service_manager_executedocker_service_manager_systemddocker_service_manager_sysvinitdocker_service_manager_upstart

Chef selects defaults with the provider resolution system

…

…

Compose resources Most specific to least specific

Enjoy

fin