DevOps Classroom Series – 19/Apr/2020

Setup

• Kitchen Setup: We already have it
• Chef Infra Server and Chef-client node:
  • Ensure you have one centos and one ubuntu bootstrapped

Ohai

• Login into the chef-client-nodes and execute ohai and now execute ohai > nodeinfo.json
• Navigate to attributes section of the node as shown in the chefserver UI
• These attributes can be used in recipe dsl as node object.

What happens during chef-convergance

Attributes

• Attribute is some information about the node or application or anything which can be represented
• Attributes are of two types
  • automatic attributes collected by ohai during chef-client cannot be changed by user
  • custom attributes can be changed at various places

Practical Explanation

• Im trying to acheive lamp stack (without mysql) in centos 7 and ubuntu 18 ubuntu and centos

• Lets generate a cookbook for apache

cd <chef-repo>\cookbooks\
chef generate cookbook -b apache

• Manual Steps:

Ubuntu:
sudo apt-get update
sudo apt-get install apache2 -y
sudo systemctl enable apache2
sudo systemctl start apache2
sudo apt install php libapache2-mod-php php-mysql php-cli
sudo systemctl restart apache2
sudo vi /var/www/html/info.php
<?php phpinfo(); ?>

Centos:
sudo yum install httpd -y
sudo systemctl enable httpd
sudo systemctl start httpd
sudo yum install php php-mysql php-fpm
sudo systemctl restart httpd
sudo vi /var/www/html/info.php
<?php phpinfo(); ?>
sudo systemctl restart httpd

• Generate a recipe for apache

chef generate recipe . install

• Now inside install.rb file lets write resource for apt-get update and it has to run only on ubuntu machines for that we write

# write an if condition
#
# Cookbook:: .
# Recipe:: install
#
# Copyright:: 2020, The Authors, All Rights Reserved.

# i want to run this cookbook only if the node is debian

# write an if condition
if node['platform'] == 'ubuntu'
    apt_update 'updateubuntu' do
        ignore_failure true
        action :update
    end
end

• chef gives us one better alternative for writing if conditions using guards Refer Here

#
# Cookbook:: .
# Recipe:: install
#
# Copyright:: 2020, The Authors, All Rights Reserved.

# i want to run this cookbook only if the node is debian

apt_update 'updateubuntu' do
    ignore_failure true
    action :update
    only_if node['platform'] == 'ubuntu'
end

• Now to write the installation we can use apt_package resource but this works only on ubuntu, chef has a generic package resource refer here
• Now create a variable and assign the value of the variable depending on platform family

#
# Cookbook:: .
# Recipe:: install
#
# Copyright:: 2020, The Authors, All Rights Reserved.

# i want to run this cookbook only if the node is debian

apt_update 'updateubuntu' do
    ignore_failure true
    action :update
    only_if node['platform'] == 'ubuntu'
end

if node['platform_family'] == 'debian'
    package_name = 'apache2'
    
elsif node['platform_family'] == 'rhel'
    package_name = 'httpd'
end

package package_name do
    action :install
end

• It is a best practice in chef to use attribute to store variables which might change, so lets go and define custom attribute
• Lets generate an custom attribute file called as default

chef generate attribute . default
# A new folder attributes will be generated inside the cookbook

• Attributes in the attributes file should be defined like how the node object appears, becoz attributes become part of your node object.

<type>['cookbookname']['purpose'] = '<value>'

• As of now only type which i want you to use is default

default['apache']['packagename'] = 'apache2'
default['tomcat']['conf_file'] = '/var/lib/tomcat7/tomcat.conf'

• The default.rb file in attributes will appear as

if node['platform_family'] == 'debian'
    default['apache']['package_name'] = 'apache2'
    
elsif node['platform_family'] == 'rhel'
    default['apache']['package_name']
end

• Now recipe install.rb looks as shown below

#
# Cookbook:: .
# Recipe:: install
#
# Copyright:: 2020, The Authors, All Rights Reserved.

# i want to run this cookbook only if the node is debian

apt_update 'updateubuntu' do
    ignore_failure true
    action :update
    only_if { node['platform'] == 'ubuntu' }
end

# using the attribute defined in the attributes/default.rb file
package node['apache']['package_name'] do
    action :install
end

# enable the apache service
service node['apache']['package_name'] do
    action :enable
end

• Lets upload the recipe and do the chef convergance

berks install
berks upload
# change run_list

• Change the run_list for centos and ubuntu node and look what happens during converge
• In chef cookbook you cannot have two resources of same type with same name use service resource twice in install.rb as shown below

#
# Cookbook:: .
# Recipe:: install
#
# Copyright:: 2020, The Authors, All Rights Reserved.

# using the attribute defined in the attributes/default.rb file
package node['apache']['package_name'] do
    action :install
end

# enable the apache service
service node['apache']['package_name'] do
    action :enable
end

# two resources of same type cannot have same name so workaround
service 'starting apache ' do
    service_name node['apache']['package_name']
    action :start
end

• Now upload the cookbook after changing the version in metadata.rb file and apply convergance. (Run-list as of now picks the latest version)

berks upload

• If you look at the whole manual steps, there are systemctl commands appearing thrice and giving three different names doesn’t sound like a good idea.
• Chef has a concept of Notifications Refer Here
  • we will be using notifications to define the service once and using it multiple times
  • Notifications are of two types notifies/subscribes
• Now lets apply notifies to service resource install
• Now we want to install multiple pacakges for that we would use loop and for that we use each in ruby
• Navigate to attributes/default.rb and change as shown below

if node['platform_family'] == 'debian'
    default['apache']['package_name'] = 'apache2'
    default['apache']['php_packages'] = ['php', 'libapache2-mod-php', 'php-mysql', 'php-cli']
    
elsif node['platform_family'] == 'rhel'
    default['apache']['package_name'] = 'httpd'
    default['apache']['php_packages'] = ['php','php-mysql', 'php-fpm']
end

• Also look into string interpolation over here
• To accomodate these in install.rb in recipes

#
# Cookbook:: .
# Recipe:: install
#
# Copyright:: 2020, The Authors, All Rights Reserved.

# using the attribute defined in the attributes/default.rb file

package_name = node['apache']['package_name']


package node['apache']['package_name'] do
    action :install
    notifies :enable, 'service[apache]'
end

service 'apache' do
    service_name node['apache']['package_name']
    action :nothing
end

packages = node['apache']['php_packages']

packages.each do |package_now|
    package package_now do
        action :install
        notifies :restart, 'service[apache]'
    end
end

• Now upload this cookbook and test it out

berks upload
# do convergance

Exercise:

• First execute what i have done in the class on chef nodes
• Try doing the same thing on kitchen