Cookbook Reusability - Speaker Deck

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Cookbook Reusability! Chef Community Summit 2014

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Sean OMeara! [email protected]! @someara

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whoami

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A Year in Review

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Diversiﬁcation

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7zip! apache2! ark! application*! couchdb! Imagemagick! java

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logrotate! mercurial! munin! nagios! nginx! ntp! openvpn

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pacman! postgresql! python! reprepro! rabbitmq! runit! supervisor

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selinux! tmux! varnish ! wordpress!

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Supermarket https://www.ﬂickr.com/photos/mobilestreetlife/10885044043

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• Escaped the tyranny of JIRA! • Moved to Github Issues! • Automated CLA checking! • OSS Artifact Repository

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Rewrites

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2009 0.5.2 Chef Vagrant ChefSpec 0.1.0 0.0.2 Minitest-Chef Berkshelf Test Kitchen 2010 0.9.0 2011 0.10.0 2012 10.12.0 1.0.0 0.2.0 1.0.0 0.7.0 1.0.0 2013 2014 1.0.0 2.0.0 1.0.0 2.0.0 1.4.0 11.0.0 12.0.0 1.6.5 3.0.0 3.0.0 1.2.2 ServerSpec ChefDK 0.0.1 2.0.0 0.2.2 TDI Capability 0.8.0

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yum! yum-*! jenkins! mysql! httpd

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The Evolution of a Chef Cookbook

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Stage 1 - Paradise https://www.ﬂickr.com/photos/nattu/1385100375/

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test / repair test / repair test / repair

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Easy to read Easy to grok Easy to test }

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Stage 2 - if statements

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logic compiled into resource collection

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Resource DSL } Just Ruby }

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Resource DSL } Just Ruby } }Chef

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Stage 3 - Crazytown https://www.ﬂickr.com/photos/kwl/4595324641

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wat

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Why?

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Reusable is useful

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Cross-platform is useful

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We desire useful things

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Platform idioms are hard

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Keeping the Dream Alive https://www.ﬂickr.com/photos/kalexanderson/7014655351/

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Most people just write their own cookbooks from scratch

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I really really really want reusable cross-platform cookbooks

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Lessons Learned

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Attributes are routinely abused https://www.ﬂickr.com/photos/jabberwocky381/2828863789

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Attributes are an interface

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Attributes are tunable knobs

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You probably just want a variable

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Or even a method

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Using an attribute to track state during a Chef run causes tears and sorrow

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Prefer resource parameters

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Primitives are more useful than opinionated policy

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“They’re Just Resources”! ! LWRP is Googleable

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Zoom out a level! ! Think about services and runtimes, not ﬁles and processes

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Singleton resources are good but confusing. Possibly even dangerous.! ! Multiple instance support is better! ! Cross-platform resources are best

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BDD / TDD yields high quality cookbooks https://www.ﬂickr.com/photos/glenirah/4376553184

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Test Kitchen! ServerSpec / Minitest / Bats! ChefSpec

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Full test coverage is tedious

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Full test coverage is totally worth it

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Let users bring their own conﬁgurations

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It is better to add to a resource_collection than to monkey patch it

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Conﬁguration ﬁles are the brains of a service

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Manage minimal conﬁguration to get a service running

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Ofﬂoad further conﬁguration to the user

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conf.d is your friend

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Hide everything else inside a resource

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Add resource parameters when appropriate

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Cross-platform cookbooks are hard https://www.ﬂickr.com/photos/glenirah/4376553184

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Cross-platform resources are even harder

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They can be done!

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Create a resource

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Create a provider

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Subclass platform providers

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Set provider default for platforms

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Do Repeat Yourself

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Some resources are often the duplicated across providers

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That’s ﬁne. It’s the pattern as a whole that’s important

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Maximize for grokability

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People will be reading your code for the ﬁrst time during operations work

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Init systems are annoying

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Using a service resource usually requires ﬁle or template resources in addition to service[thingd]

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Debconf! Docker! LaunchD! Runit! SMF! Simple! SystemD! Sysvinit! Upstart! Windows Services