Exploring "Infrastructure as code" with Opscode Chef Part 6 (Refactoring cookbooks)

Refactoring a cookbook refers to the process of breaking down a recipe into smaller parts & storing them separately.

Let's refactor the apache cookbook:

[sahil@cwork recipes]$ cat default.rb
#
# Cookbook Name:: apache
# Recipe:: default
#
# Copyright 2016, YOUR_COMPANY_NAME
#
# All rights reserved - Do Not Redistribute
#


package_name = "httpd"
service_name = "httpd"
doc_root = "/var/www/html"


if node["platform"] == "ubuntu"
   package_name = "apache2"
   service_name = "apache2"
   doc_root = "/var/www"
end


package package_name do
  action :install
end

service service_name do
  action [:start, :enable]
end

#cookbook_file "#{doc_root}/index.html" do
 # source "index.html"
  #mode "0644"
#end


template "#{doc_root}/index.html" do
  source "index.html.erb"
  mode "0644"
end


From this cookbook  we can take the conditional logic part responsible for identifying the platform & the variable declarations & put them in a separate file cookbooks/apache/attributes/default.rb. We'll modify the if statement to a case statement:

case node["platform"]

when "centos"
default["package_name"] = "httpd"
default["service_name"] = "httpd"
default["doc_root"] = "/var/www/html"

when "ubuntu"
default["package_name"] = "apache2"
default["service_name"] = "apache2"
default["doc_root"] = "/var/www"
end

With this done, we'll need to modify our cookbook as well which now looks like:

package node["package_name"] do

  action :install

end

service node["service_name"] do

  action [:start, :enable]

end

template "#{node["doc_root"]}/index.html" do

  source "index.html.erb"

  mode "0644"

end

Introducing dependencies in cookbooks:

We can make cookbooks dependent on other cookbooks such that the dependencies get applied before the main cookbook is run. For example, if I want to introduce a dependency in the apache cookbook I need to edit the cookbooks/apache/metadata.rb file & add the following line:

depends       cook_book_name

Note: We can also update the cookbook version by editing this file.


Defining a custom attribute:

We can define a custom attribute for a client node that is not returned by OHAI by default. To do this we need to edit the cookbook_name/attributes/default.rb file & define the custom attribute. For example:

default["company"] = "TEST_COMPANY"

After defining this attribute we can use it in erb files for our recipes.


Roles introduction:

Roles allow you to encapsulate the run lists & attributes required for a server to perform a function as per user expectation. Roles make it easy to configure many nodes identically avoiding repetition.

Creating a role:
We'll create a role called webservers. Create a webservers.rb file in chef-repo/roles path with the following content:

name "webserver"
description "web servers"
run_list "recipe[apache], recipe[testrecipe]"
default_attributes({
            "company" => "NEW_COMPANY"
})

Custom attributes defined in roles will override the ones defined in individual cookbooks.

To upload a role type the following command:

sudo knife role from file webservers.rb

To view available roles type:

sudo knife role list

To view details of a role:

sudo knife role show webservers

To add the role to the node's run list, modify the run list from the chef server GUI.


Environments:

An environment includes the attributes necessary for for configuring the infrastructure in that environment. Environments allow use to share cookbooks & roles & isolate resources within a single organization. An interesting feature of environments is that they allow cookbook version constraints to be implemented.

To create an environment: 
Under chef-repo/environments directory create a .rb file for the specific environment. For example dev.rb to represent the dev environment. Populate this file with the following content:

name "development"
description "development environment"
cookbook "apache", "=2.0.0"

To view available versions of a cookbook type:

sudo knife cookbook show cookbook_name

To upload an environment to the chef server type:

sudo knife environment from file dev.rb

You can modify the environment attribute of a node from the chef server web interface.