Customizing Chef for Fun and Profit

Customizing Chef
For Fun and Profit

@jonlives
Jon Cowie
Sr Operations Engineer

@jonlives
Beginning of 2010 Today

@jonlives
Chef at Etsy
• Open Source Chef Server 
• ~1500 Nodes 
• CentOS, some Mac OS X

@jonlives
Absorb what is
useful.
Discard what is
useless.

@jonlives
“I am not smart enough to
build an ontology … that
can encompass all the
variations in infrastructure.
Nobody is, the world
moves too fast.”

@jonlives
There is no
magic pill.

@jonlives
Get Config Data / Initialize
• Load client.rb
• Server URL
• Auth Credentials
• Paths
• Run ohai
• Collect attributes
• Plugins!

@jonlives
Ohai Plugins
• Add attributes to your
node
• Executed at start of
run
• Single Ruby file
• Highest precedence

@jonlives
Ohai Plugins - v6
provides ‘awesome’
!
awesome Mash.new
awesome[:sauce] = "Sricacha"
awesome[:level] = "11"

@jonlives
Ohai Plugins - v7 (Coming soon!)
Ohai.plugin(:Awesome) do
provides "awesome"
collect_data(:darwin) do
awesome Mash.new
awesome[:sauce] = “Sriracha"
awesome[:level] = 11
end
end

@jonlives
Ohai Plugins - client.rb / solo.rb
Ohai::Config[:plugin_path] << /<path>/plugins

@jonlives
Authenticate / Register
• Authenticate to Server
• <clientkey>.pem
• Register if not already
registered
• <validation>.pem
• If both fail, go directly to
jail.

@jonlives
Load / Build Node
• Download node
• Combine attributes
• Expand run_list
• Order matters!
• Create RunStatus
object
• Run start handlers

@jonlives
Handlers
• Respond to specific
situations
• Start, Report, Exception
• Common Code

@jonlives
Handlers - Common Code
require "chef/handler"
!
class HandlerName < Chef::Handler
def report
# Ruby code goes here
end
end

@jonlives
Handlers - client.rb / solo.rb
require “/path_to/mystarthandler.rb"
!
my_start_handler = MyStartHandler.new
!
start_handlers << my_start_handler

@jonlives
Synchronize Cookbooks
• Get cookbook files list
• Only required recipes,
files & templates
• Compares to local
cache
• Download changes

@jonlives
Set up RunContext
• Cookbook Collection
• Definitions List
• Events
• Notifications
• Node
• Resource Collection
• Empty for now…

@jonlives
Events
• Respond to interesting
events
• Pub / Sub model
• EventDispatch::Base
• Formatter
• Custom Subscriber

@jonlives
Events - Custom Subscriber
require “chef/event_dispatch/base"
!
class AwesomeSubscriber < Chef::EventDispatch::Base
def run_started(run_status)
…
end
# Method for each interesting event
end

@jonlives
Events - Register Subscriber
require "chef/handler"
require “/path/awesome_subscriber.rb'
!
class AwesomeSubscriberStartHandler < Chef::Handler
def report
event_dispatcher_subscriber = AwesomeSubscriber.new
@run_status.events.register(event_dispatcher_subscriber)
end
end

@jonlives
Load Cookbook Data
• Populate Resource
Collection
• Libraries
• Attributes
• Resources / Providers
• Definitions
• Recipes

@jonlives
Converge Node
• Actually changes node
• Apply resource
collection
• Again, order matters!

@jonlives
Finalize
• Successful Run
• Save Node
• Report Handlers
• Failed Run
• Exception Handlers
• 💩

@jonlives
Report & Exception Handlers
def report
if @run_status.success?
# Do a happy dance
elsif @run_status.failed?
# Sad panda.
end
end

@jonlives
Handlers - client.rb / solo.rb
require “/var/chef/handlers/mystarthandler.rb"
require "/var/chef/handlers/mynewhandler.rb"
!
my_start_handler = MyStartHandler.new
my_new_handler = MyNewHandler.new
!
start_handlers << my_start_handler
report_handlers << my_new_handler
exception_handlers << my_new_handler

@jonlives
That RunStatus Object Again…
• Accessible to handlers
• Run status & timings
• Exception and Backtrace
• All & updated resources
• RunContext
• Node object

@jonlives
Don’t fear the code!
• https://github.com/opscode/chef
• lib/chef/handler.rb
• lib/chef/run_status.rb
• lib/chef/run_context.rb
• lib/chef/event_dispatch/base.rb

@jonlives
Criteria for Customization
Simplicity
Modularity
Visibility
Maintainability
Scalability

@jonlives
November 2014
!
http://jonliv.es/book
!
O’Reilly Stand

@jonlives
Thanks!
Questions?
!
Office Hours @ 3.15, Marina Room
@jonlives / http://jonliv.es / jcowie@etsy.com

Customizing Chef for Fun and Profit

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