Reusable Chef Cookbooks

The Evolution

Phase 1

Cookbook as a big bash script

Example

bash "install mypackage" do
  cwd "#{Chef::Config[:file_cache_path]}"
  code <<-EOH
wget http://example.com/mypackage-1.0.tar.gz
tar xzf mypackage-1.0.tar.gz
cd mypackage-1.0
./configure && make && make install
  EOH
  not_if { File.exists?("/usr/bin/mypackage") }
end

Pros

Fast and Easy

Cons

Everything else

Phase 2

Customize using attributes

Example

filename =
  "mypackage-#{node[:mypackage][:version]}.tar.gz"
bash "install mypackage" do
  cwd "#{Chef::Config[:file_cache_path]}"
  code <<-EOH
wget http://example.com/#{filename}
tar xzf #{filename}
cd mypackage-#{node[:mypackage][:version]}
./configure && make && make install
  EOH
  not_if { File.exists?("/usr/bin/mypackage") }
end

template "/etc/mypackage.conf" do
  source "mypackage.conf.erb"
  mode "0644"
  variables(
      :database => node[:mypackage][:database],
      :user => node[:mypackage][:user],
      :password => node[:mypackage][:password]
    )

Pros

Easy to customize environment specific settings

Cons

Does not allow customization of components installed

Phase 3

Partition recipes into units of reuse

Example

include_recipe "mypackage::default"
# Include different recipes based on
# nodes characteristics
if node['datacenter'] != 'BWD'
  include_recipe "mypackage::db_auth"
else
  include_recipe "mypackage::ad_auth"
end

Pros

Easy to customize the install for different nodes

Cons

Can not loop over recipes for repetition

Phase 4

Abstract repeated actions using resources

Example

glassfish_mq_destination "WildfireStatus queue" do
  queue "Fireweb.WildfireStatus"
  config {'validateXMLSchemaEnabled' => true,
          'XMLSchemaURIList' => 'http://...'}
  host 'localhost'
  port 7676
end

Composable Example

glassfish_mq "MessageBroker Instance" do
  instance "MessageBroker"
  users {...}
  access_control_rules {...}
  config {...}
  queues {
    "Fireweb.WildfireStatus" =>
            {'validateXMLSchemaEnabled' => true,
             'XMLSchemaURIList' => 'http://...'}
  }
  port 7676
  admin_port 7677
  jms_port 7678
  jmx_port 8087
  stomp_port 8088
end

Pros

Reduce repetition of similar code
Composable abstractions
Simplify the cognitive load

Cons

Still repetitive if you need to define 30 queues
Multiple products require updates to a single cookbook

Phase 5

Data driven reuse

synthesize using search
load from data bags or external data store
synthesize using rule layer

Search Example

queues = []
search(:node, 'omq_dests_queues:* AND ' +
              'NOT name:' + node.name) do |n|
  queues.merge( n['omq']['dests']['queues'].to_hash )
end
queues.merge( node['omq']['dests']['queues'].to_hash )

queues.each_pair do |key, value|
  glassfish_mq_destination key do
    queue key
    config value
    host 'localhost'
    port 7676
  end
end

Pros

Reduce typing to minimal set

Cons

Mixes policy into cookbook

Phase 6

Separate policy into paired cookbook

Derive data in cookbook A
Set attributes on the node
include recipe in cookbook B

Example

search(:node, 'omq_dests_queues:* AND ' +
              'NOT name:' + node.name) do |n|
  n.to_hash.each_pair do |key, value|
    node.override['omq']['dests']['queues'][key] = value
  end
end
include_recipe "glassfish::attribute_driven_mq"

Phase 7

Standardize policy, Customize using attributes

Example

node.override['graphite']...['schema_search']['filter'] =
  "monitor_environment:#{node.chef_environment}"
include_recipe "graphite::search_based"

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Reusable Chef Cookbooks

The Evolution

Phase 1

Cookbook as a big bash script

Example

Pros

Cons

Phase 2

Customize using attributes

Example

Pros

Cons

Phase 3

Partition recipes into units of reuse

Example

Pros

Cons

Phase 4

Abstract repeated actions using resources

Example

Composable Example

Pros

Cons

Phase 5

Data driven reuse

Search Example

Pros

Cons

Phase 6

Separate policy into paired cookbook

Example

Phase 7

Standardize policy, Customize using attributes

Example

Peter Donald

peter at realityforge.org,

@rahvintaka