I have been learning from this book Fabio Alessandro Locati, published under Packt>. The example can be found at https://github.com/PacktPublishing/Learning-Ansible-2.X-Third-Edition/tree/master/Chapter04

Today I am learning about working with local_action feature. This feature allows us to run certain tasks locally on the machine that runs Ansible rather than logging into a remote box and running these commands.

--- 
- hosts: database 
  remote_user: vagrant
  tasks: 
    - name: Count processes running on the remote system 
      shell: ps | wc -l 
      register: remote_processes_number 
    - name: Print remote running processes 
      debug: 
        msg: '{{ remote_processes_number.stdout }}' 
    - name: Count processes running on the local system 
      local_action: shell ps | wc -l 
      register: local_processes_number 
    - name: Print local running processes 
      debug: 
        msg: '{{ local_processes_number.stdout }}' 

Delegating a Task

If you wish to execute an action a different system. For example, you may want to do something on a database node while working on an application node or a localhost, you can use the delegate_to: HOST Property. This is useful when there are complex procedures need to be executed by the local machine or any other machine

--- 
- hosts: database 
  remote_user: vagrant
  tasks: 
    - name: Count processes running on the remote system 
      shell: ps | wc -l 
      register: remote_processes_number 
    - name: Print remote running processes 
      debug: 
        msg: '{{ remote_processes_number.stdout }}' 
    - name: Count processes running on the local system 
      shell: ps | wc -l 
      delegate_to: localhost 
      register: local_processes_number 
    - name: Print local running processes 
      debug: 
        msg: '{{ local_processes_number.stdout }}' 

Working with Conditionals

Ansible provides conditional statements to run a task only when a specified condition(s) is met

--- 
- hosts: webserver 
  remote_user: vagrant
  tasks: 
    - name: Print the ansible_os_family value 
      debug: 
        msg: '{{ ansible_os_family }}' 
    - name: Ensure the httpd package is updated 
      yum: 
        name: httpd 
        state: latest 
      become: True 
      when: ansible_os_family == 'RedHat' 
    - name: Ensure the apache2 package is updated 
      apt: 
        name: apache2 
        state: latest 
      become: True 
      when: ansible_os_family == 'Debian' 

Boolean Conditionals

Apart from matching string, you can check whether a variable is true. Ansible provides a way to check whether a variable is defined. The below features allow us to put the Ansible playgroup in a failure state if the backup_folder is not set

--- 
- hosts: all 
  remote_user: ansible 
  vars: 
    backup: True 
  tasks: 
    - name: Check if the backup_folder is set 
      fail: 
        msg: 'The backup_folder needs to be set' 
      when: backup_folder is not defined 
    - name: Copy the crontab in tmp if the backup variable is true 
      copy: 
        src: /etc/crontab 
        dest: '{{ backup_folder }}/crontab' 
        remote_src: True 
      when: backup 

Working with Handlers

Every handler will run at the end of the playbook if notified. Ansible will make sure, how many times you notify the service, it will call that task once after all other tasks has completed.

--- 
- hosts: webserver 
  remote_user: vagrant
  tasks: 
    - name: Ensure the HTTPd package is installed 
      yum: 
        name: httpd 
        state: present 
      become: True 
    - name: Ensure the HTTPd service is enabled and running 
      service: 
        name: httpd 
        state: started 
        enabled: True 
      become: True 
    - name: Ensure HTTP can pass the firewall 
      firewalld: 
        service: http 
        state: enabled 
        permanent: True 
        immediate: True 
      become: True 
    - name: Ensure HTTPd configuration is updated 
      copy: 
        src: website.conf 
        dest: /etc/httpd/conf.d 
      become: True 
      notify: Restart HTTPd 
  handlers: 
    - name: Restart HTTPd 
      service: 
        name: httpd 
        state: restarted 
      become: True