DevOps Classroom Series – 29/Aug/2020

Lets create a cookbook to install lamp server on Ubuntu instances

• For this installation we need manual steps, Refer Here for detailed documentation.
• In this exercise we will not be installing mysql-server
• The manual steps which we will automate initially are

sudo apt-get update
sudo apt install apache2 -y
sudo apt install php libapache2-mod-php php-mysql -y
sudo apt install php-cli -y

• So lets create our cookbook

chef generate cookbook -b mylamp

• For developing cookbooks in chef, lets use visual studio with an chef extension installed
• The extension installed will help in developing cookbooks.
• Lets navigate to default.rb in recipes folder and start writing resources
• Now if we automate every step mentioned above in chef, the default.rb in recipes folder will be as shown below

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

# Manual Step: sudo apt-get update
apt_update 'update ubuntu packages' do
    ignore_failure true
    action :update
end

# sudo apt-get install apache2 -y
apt_package 'apache2' do
    action :install
end

# sudo apt install php libapache2-mod-php php-mysql -y
apt_package 'php' do
    action :install
end

apt_package 'libapache2-mod-php' do
    action :install
end

apt_package 'php-mysql' do
    action :install
end

# sudo apt install php-cli -y

apt_package 'php-cli' do
    action :install
end

• Now lets upload the cookbook to chef server (This time using a tool called as berks)

# execute once after you create a cookbook
berks install

# use this command to upload cookbook (multiple times)
berks upload

• Now verify the cookbook in the chef server management ui
• Now we need to add the recipe to the run_list of the node
• Lets understand the term called as configuration drift. Configuration drift is a state where there is difference in the desired state mentioned in the cookbook and actual state on the node
• During convergence chef-server will send the recipes (and all the other required files to run recipes) in the run-list mentioned to the chef-node to be executed by chef-client
• For this series we are manually forcing convergence by executing sudo chef-client on the node
• Now try to access http://<public-ip-node&gt;
• While we writing this cookbook we have used the same resource with different values multiple times

apt_package 'apache2' do
    action :install
end

# sudo apt install php libapache2-mod-php php-mysql -y
apt_package 'php' do
    action :install
end

apt_package 'libapache2-mod-php' do
    action :install
end

apt_package 'php-mysql' do
    action :install
end

# sudo apt install php-cli -y

apt_package 'php-cli' do
    action :install
end

• So now lets correlate this situation with some basic programming
  1. Approach 1

  print('apache2')
  print('php')
  print('php-mysql')
  

  2. Approach 2

  names = ['apache2', 'php', 'php-mysql']
  for(name in names):
      print(name)
  

• Generally we use approach 2 as writing number of lines of print doesn’t make sense
• So, should we not apply same approach for our recipe in chef
• In chef, if we have to use the better way, lets try to understand little bit of ruby.
• Next Steps:
  • Just Enough Ruby for Chef. Refer Here for chef docs on Ruby.
  • Test Driven Development of Chef cookbooks using test kitchen.