what makes a good chef cookbook? (may 2014 edition)

What Makes a Good Cookbook?Julian C. DunnSenior Consulting Engineer Engineering Team LeadChef Software, Inc.<jdunn@getchef.com>

$ whoami•Consulting Engineer Engineering Team Lead at Chef

•System Administrator

•Reformed Java Developer

•Writes silly code like this

•https://github.com/juliandunn/doge-chef-formatter

Finding a Good CookbookLMGTCFY

Do judge a cookbook by its cover

missing_attrs = %w{ postgres }.select do |attr| node['postgresql']['password'][attr].nil? end.map { |attr| "node['postgresql']['password']['#{attr}']" }

if !missing_attrs.empty? Chef::Application.fatal!([ "You must set #{missing_attrs.join(', ')} in chef-solo mode.", "For more information, see https://github.com/opscode-cookbooks/postgresql#chef-solo-note" ].join(' '))end

Too Clever for Its Own Good

Chef::Application.fatal!([ "You must set #{missing_attrs.join(', ')} in chef-solo mode.", "For more information, see https://github.com/opscode-cookbooks/postgresql#chef-solo-note" ].join(' '))

Poking at Chef Internals

•Other abuses: Messing with run_context and run_state

if node.run_list.recipes.include?('foo::bar')...end

Poking run_list and environment

if node.chef_environment == 'production'...end

• Use feature flags!

template "/etc/whatever.conf" do ... not_if { foo }end

Compile vs. Execute Errors

if foo template "/etc/whatever.conf" do ... endend

not the same thing as

execute 'yum install httpd' do not_if 'rpm -qa | grep -x httpd'end

Not declarative

•Also, the Chef recipe with 100 bash or powershell_script resource declarations

execute '/i/will/run/every/time' do action :run # because I don't have a guard hereend

Missing guards

default['mydaemon']['port'] = '1433'# don't you mean the integer 1433?default['mydaemon']['knob'] = 'disabled' # don't you mean false?

Not using native Ruby data types

• If you use native data types you can validate people’s input.

Fear of LWRPs•Missed abstraction opportunities

•No good example to put here; they’re all 200 lines long (thus proving my point)

remote_file 'whatever.tar.gz' do source 'http://hardcoded.url.com/'end

Hardcoded Strings

Excess Conditions & Recipe Length•https://github.com/opscode-cookbooks/mysql/blob/v3.0.12/recipes/server.rb

• (We’ve since refactored this)

Good Cookbooks...

Put control flow in attributes•Especially for cross-platform cookbooks

•Set common set of attributes, write common behavior in recipe context

case node['platform']

when "debian", "ubuntu" default['postgresql']['client']['packages'] = %w{postgresql-client libpq-dev} default['postgresql']['server']['packages'] = %w{postgresql} default['postgresql']['contrib']['packages'] = %w{postgresql-contrib}

when "fedora", "amazon" default['postgresql']['client']['packages'] = %w{postgresql-devel} default['postgresql']['server']['packages'] = %w{postgresql-server} default['postgresql']['contrib']['packages'] = %w{postgresql-contrib} default['postgresql']['server']['service_name'] = "postgresql"

when "redhat", "centos", "scientific", "oracle" default['postgresql']['version'] = "8.4" default['postgresql']['dir'] = "/var/lib/pgsql/data"

if node['platform_version'].to_f >= 6.0 default['postgresql']['client']['packages'] = %w{postgresql-devel} default['postgresql']['server']['packages'] = %w{postgresql-server} default['postgresql']['contrib']['packages'] = %w{postgresql-contrib} else default['postgresql']['client']['packages'] = ["postgresql#{node['postgresql']['version'].split('.').join}-devel"] default['postgresql']['server']['packages'] = ["postgresql#{node['postgresql']['version'].split('.').join}-server"] default['postgresql']['contrib']['packages'] = ["postgresql#{node['postgresql']['version'].split('.').join}-contrib"] end default['postgresql']['server']['service_name'] = "postgresql"

end

Control Flow in Attributes

node['postgresql']['server']['packages'].each do |pg_pack|

package pg_pack

end

Common Recipe Code

•Easy to support more platforms without modifying recipe

default.rb

server.rb

_suse.rb_fedora.rb_windows.rb

Separate recipes by OS• If things you do are very different per platform, separate them into different recipes

“Public” versus “Private” recipes• ‘_’ faux-namespacing

loaded_recipes = if run_context.respond_to?(:loaded_recipes) run_context.loaded_recipes else node.run_state[:seen_recipes] end

node['mysql']['client']['packages'].each do |name| resources("package[#{name}]").run_action(:install)end

Do not abuse compile-time

•.run_action(:must_die)

•Use sparingly, if at all!

if some_error_condition fail "Helpful error message" # rather than Chef::Application.fatal!("error")end

Avoid poking Chef Internals

•Chef::Application.fatal is for use by Chef itself

•fail or raise is better

Attributes only where necessary• “Let’s create a node attribute for each of the 15,000 tunables in this daemon”

•Not necessary if you never touch 14,975 of those knobs

git clone git://github.com/foozolix/foozolix.git

cd foozolix && ./configure

make

make install

Give people options for installation

•At least give people a way to install from packages.

• “Compile from source” should be banned in most cases.

Be declarative•Know and use built-in Chef resources

•Know where to find LWRPs to avoid batch/execute/powershell_script

•Consider log resource versus Chef::Log

•Shows up in reporting as an updated resource instead of having to trawl through client.log

•Set an idempotency guard!

•Log at the right log level

Run System Commands Safely• system

•backticks

•Chef::Mixin::ShellOut

•shell_out

•shell_out!

$ chef-apply -s

Chef::Recipe.send(:include, Chef::Mixin::ShellOut)

cmd = shell_out!("echo -n Ohai, world")log cmd.stdout^DRecipe: (chef-apply cookbook)::(chef-apply recipe) * log[Ohai, world] action write

Example Recipe Context

unless node.chef_environment('pigsty') include_recipe 'bacon::default'end

Feature Flags Example

if node['foo']['bar']['can_haz_bacon'] include_recipe 'bacon::default'end

• Instead:

node['jboss']['instances'].each do |instance| link "/etc/init.d/#{instance['name']}" do to "/etc/init.d/jbossas" end

template "/etc/sysconfig/#{instance['name']}" do source "jbossas.sysconfig.erb" owner node['jboss']['server']['user'] group node['jboss']['server']['group'] mode "00644" variables( :jbossconf => instance['name'] ) action :create end

template "#{node['jboss']['server']['home']}/bin/standalone.sh" do source "standalone.sh.erb" owner node['jboss']['server']['user'] group node['jboss']['server']['group'] mode "00755" action :create end link "#{node['jboss']['server']['home']}/bin/#{instance['name']}.sh" do to "#{node['jboss']['server']['home']}/bin/standalone.sh" endend

Repetition == LWRP Candidate

actions :create, :delete

attribute :instance_name, :kind_of => String, :name_attribute => trueattribute :console_log_level, :kind_of => String, :required => trueattribute :datasources, :kind_of => Hash, :default => {}

.

.

.

default_action :create

Repetition == LWRP Candidate•Perfect for abstracting!

•Resource interface:

jboss_instance "petstore" do instance_name "can_haz_cheezburgerz" console_log_level "DEBUG" datasources {'db1' => 'jdbc://whatever:5432/db1'}end

Repetition == LWRP Candidate

•Write/debug hard logic once

•Clear consumer interface

•Parameter validation & sanity checking

•Non-JBoss experts can invoke without knowing gnarly details

module MyCookbook module Helper

# returns Windows friendly version of the provided path, # ensures backslashes are used everywhere def win_friendly_path(path) path.gsub(::File::SEPARATOR, ::File::ALT_SEPARATOR) if path end end end

Write helper libraries

•Create reusable helper functions in pure Ruby

•Move repetitive detail out of recipe context.

•http://tinyurl.com/chef-libraries

Keep Recipes Small•< 100 lines

• If longer than this, consider breaking up functionality

•Example: nagios::server recipe does too much

• Installs Nagios

•Configures Nagios

•Pokes around in data bags for config items

Use Community Helpers•Chef Sugar - http://code.sethvargo.com/chef-sugar/

•Chef Cutlery - https://github.com/realityforge/chef-cutlery

•Attribute Validator - https://github.com/clintoncwolfe/attribute-validator

•You can also crib the ideas if you want to avoid external dependencies

Wrap-Up

Testing• I didn’t mention testing once in this talk!

• I’m assuming you will write tests for your cookbooks.

•A whole other talk...

• ... including good/bad things to test

Make your code aromatic•Keep recipes small

•Keep recipes simple

•Use a consistent style

•Use Foodcritic

Beware Expertise Bias•Hide gnarly details from recipe context

•Libraries

•LWRPs

•Attributes

•Resist urge to be overly clever - not everyone’s an expert

•Akin to the one-line sed/awk script

•http://tinyurl.com/the-expertise-bias

Learn from Software Developers•Everything I told you about information hiding, design patterns, testing, etc.

•Ops can learn from devs as well!

•Maybe we should call it OpsDev...

Don’t Yet Know Chef?•2-Day Chef Fundamentals Training in Boston

• June 16-17

•New Horizons, 75 Federal St., Suite 1205

•Use code MEETUP to save 10%

Thank You!E: jdunn@getchef.comG: https://github.com/juliandunnT: @julian_dunnW: www.juliandunn.net