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Hand Crafted Artisanal Chef Resources
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Config Management Camp Ghent, Belgium February 2016
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Sean OMeara
[email protected]
@someara
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whoami
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Part 1
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Writing library cookbooks An opinionated workflow Step by step
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Step 1 - Disregard dogma “Unit tests first” is a dirty lie https://flic.kr/p/aTSiXF
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Step 2 - Make things up Then work backwards https://flic.kr/p/dXkQ5s
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Contrived examples are the best examples
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Place this off to the side, we will come back for it later.
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Step 3 - Create a cookbook By hand. Be a wizard. https://flic.kr/p/3mMW6e
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mkdir -p ~/src/custom-resources-tutorial cd ~/src/custom-resources-tutorial emacs metadata.rb
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Step 4 - Embed a test cookbook. By hand. Be a wizard. Again. https://flic.kr/p/ai36NG
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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
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Step 5 - Tell Berkshelf about it https://flic.kr/p/k5jmja
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cd ~/src/custom-resources-tutorial emacs Berksfile
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Step 6 - Configure Test Kitchen https://flic.kr/p/r38F5c
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emacs .kitchen.yml
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kitchen test ; echo $?
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Step 7 - Save game https://flic.kr/p/6ZJ4G7
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cd ~/src/custom-resources-tutorial cp ~/src/chef-cookbooks/docker/.gitignore . cp ~/src/chef-cookbooks/docker/.rubocop.yml .
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rubocop -a git init git add . git commit -a -m 'v0.0.1 - cookbook skeleton' git tag v0.0.1
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Step 8 - Use resource in test recipe https://flic.kr/p/8MuUAX
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emacs test/cookbooks/my_file_test/recipes/ default.rb
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kitchen converge ; echo $?
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Step 9 - Implement resource https://flic.kr/p/bkVKRb
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cd ~/src/custom-resources-tutorial mkdir libraries emacs libraries/my_file.rb
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kitchen converge ; echo $? kitchen converge ; echo $?
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Step 10 - Test for behavior https://i.ytimg.com/vi/1y8Rqvz-Jcg/ maxresdefault.jpgz
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mkdir -p test/integration/my_file/inspec emacs -p test/integration/my_file/inspec/ run_spec.rb
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kitchen verify ; echo $?
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Step 11 - Add specs and commit https://flic.kr/p/rrgfZh
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cd ~/src/custom-resources-tutorial mkdir spec emacs spec/spec_helper.rb
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emacs spec/my_file_spec.rb
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rubocop -a rspec ; echo $? git add . git commit -a -m “v0.1.0 - my_file resource” git tag v0.1.0
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stove 0.1.0
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Step 12 - Iterate indefinitely https://flic.kr/p/8Ny8Jt
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Congratulations, you have now written one software.
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You must now maintain it forever.
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muahaha.
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Part 2
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Custom Resources Tips and Tricks
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Be explicit https://flic.kr/p/pz1JAo
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Converge twice during development Use markers for “negative” actions https://flic.kr/p/pqwd5U
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Tests let you refactor with confidence https://flic.kr/p/4WnjM4
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STAR WIPE
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Pure Ruby resources https://flic.kr/p/5km2fM
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Pure Ruby resources utilize - The Ruby Standard Library - Chef helper libs (mixlib-shellout) - Ruby gems
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It might make sense to vendor gems
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load_current_value - Runs at converge time - Just before the action body - Loads desired state values
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converge_if_changed - Runs if any desired_state: true property differs from user input - desired_state: false avoids comparison
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coerce transforms values - Called when property is set - Called when property is read - Use this to raise errors on bad input
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The docker_container resource uses coercion heavily https://github.com/chef-cookbooks/ docker/blob/master/libraries/ docker_container.rb
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lazy defaults - Delays evaluation until used - Useful for calculated values
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Composite resources https://flic.kr/p/fm58oo
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Composite resources - Reuse Chef resources - Actions look like recipes - Do not use load_current_value
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etcd_installation_binary :create
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httpd_config_rhel :create
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Avoid leaky abstractions https://flic.kr/p/7d1kDc
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Resources should be minimalist
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Early versions might be simple
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They rarely stay that way
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Iterate and add more features Break down into smaller resources
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Use naming semantics to describe strategy
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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
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Recycle patterns as they emerge
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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
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Chef selects defaults with the provider resolution system
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…
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…
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Compose resources Most specific to least specific
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Enjoy
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fin