DevOps Classroom Series – 01/Dec/2019

Attributes

• Attributes are user variables
• Attributes can be defined at multiple places
  • Recipe
  • Attribute File
  • Roles
  • Environments
• Attributes also have types
  • default
  • force_default
  • normal
  • overrride
  • force_override
  • automatic

Scenario: Lamp

• As of now we have lamp stack cookbook with one recipe for ubuntu and one recipe for redhat.
• Lets try to write one recipe for both.
• Lets generate the attribute

chef generate attribute --help
chef generate attribute . default

• In the default.rb file generated in attributes folder, add the following

default[<cookbookname>][<variable-name>] = <variable-value>
default['apachewithphp']['package_name'] = 'apache2'

• default.rb with all the attributes defined will be as shown below

if node['platform'] == 'ubuntu'
    # package name for apache server for ubuntu machines
    default['apachewithphp']['package_name'] = 'apache2'

    # php packages for ubuntu machines
    default['apachewithphp']['php_packages'] = ["php", "libapache2-mod-php",  "php-mysql", "php-cli"]
    
else

    # package name for apache server for redhat machines
    default['apachewithphp']['package_name'] = 'centos'

    # php packages for ubuntu machines
    default['apachewithphp']['php_packages'] = ["php",  "php-mysql"]
    
end

• Using the attribute defined in attributes file can be acheived by using node object. syntax is

# attribute definition
default[<cookbookname>][<variable-name>] = <variable-value>

#attribute usage
node[<cookbookname>][<variable-name>]

• If we apply the above attributes then recipe will be as shown below

#
# Cookbook:: .
# Recipe:: phpapache
#
# Copyright:: 2019, The Authors, All Rights Reserved.

if node['platform'] == 'ubuntu'
    apt_update 'update pacakges' do
        ignore_failure true
        action :update
    end 
end


package_name = node['apachewithphp']['package_name']

package package_name do
    action :install
    notifies :enable, "service[#{package_name}]"
end

php_packages = node['apachewithphp']['php_packages']

php_packages.each do |package_name|
  package package_name do
      action :install
  end
end

#remote_file '/var/www/html/info.php' do
#    source 'https://qt-s3-new-testing.s3-us-west-2.amazonaws.com/info.php'
#    action :create
#    notifies :restart, "service[#{mypackage}]"
#end

cookbook_file '/var/www/html/info.php' do
    source 'info.php'
    action :create
    notifies :restart, "service[#{mypackage}]"
end

service package_name do
    action :nothing
end

• Lets apply only_if gaurd as mentioned over here
• Also look at not_if over here
• Lets add the logic to fail the recipe execution if it is executed on unsupported platforms. The following code is added to default.rb in recipes folder.

if node['platform'] == 'ubuntu' or node['platform'] == 'centos'
    include_recipe 'apachewithphp::phpapache'
else
    raise 'This cookbook is supported only on ubuntu and centos'
    
end

• Try testing this cookbook by changing kitchen.yaml file for ubuntu and centos flavloure
• Now change the version in the metadata.rb file and upload the cookbook using berks upload.

Making Cookbooks Reusable

• There will be lot of cookbooks already written, rather than rewriting cookbooks, it easy to reuse.
• Ways of reusing cookbooks
  • Reusing recipes
  • Making your cookbooks reusable by writing custom resources.
• Supermarket:
  • Community cookbooks with reusable recipes or reusable custom resources.

Chef Supermarket

• Lets create a cookbook to install java and postgresql on ubuntu machine and centos using chef supermarket cookbooks.
• Lets create a cookbook called supermarketdemo
• Now lets find a supermarket cookbook for postgres. Result is over here
• To use this cookbook we need to define dependency. Dependency is defined in metadata.rb file using the following syntax

depends '<cookbookname>', '<symbol> <version>'

• Symbols in versions define restrictions on versions
  • <
  • >
  • <=
  • =
  • ~>
• berks install command will download all the dependencies of your cookbook defined in metadata.rb
• Now lets try to install postgres server by reading the documentation of cookbook, the way is as following. use the custom resource.

postgresql_server_install 'Setup my PostgreSQL 9.6 server' do
    password 'MyP4ssw0rd'
    port 5433
    action :create
  end

• Try to execute this cookbook located at here