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/Chapter03

Basics

Today I am learning on working with Inventory Files. This time we are dealing with multiple hosts. These hosts have to be placed in the inventory file. An example is pasted here. In hosts.ini, we have

[Compute] 
node01.example.com 
node02.example.com
 
[Login] 
login.example.com

To run the ansible playfile

ansible-playbook -i hosts.ini firstrun.yaml

firstrun.yaml is taken from the site listed. It is to ensure the ansible user exist, accept the SSH keys and provided with sudoers rights with no password.

 hosts: all 
  user: vagrant 
  tasks: 
    - name: Ensure ansible user exists 
      user: 
        name: ansible 
        state: present 
        comment: Ansible 
      become: True
    - name: Ensure ansible user accepts the SSH key 
      authorized_key: 
        user: ansible 
        key: https://github.com/fale.keys 
        state: present 
      become: True
    - name: Ensure the ansible user is sudoer with no password required 
      lineinfile: 
        dest: /etc/sudoers 
        state: present 
        regexp: '^ansible ALL\=' 
        line: 'ansible ALL=(ALL) NOPASSWD:ALL' 
        validate: 'visudo -cf %s'
      become: True

Regular Expressions

If you have a larger number of servers with predictable names, you may want to consider the following expression. You can save 100 lines of listing the server with the following expression

[Compute] 
node[01:100].example.com 

 
[Login] 
login.example.com

Group Variables

If you wish to set a variable for the whole group, you may want to set a variable that is valid for the whole group,. A quick note from the book is that the host variables will override the group variables if the same variable is declared in both spaces.

[Compute] 
node[01:100].example.com 

[compute:vars]
firewalld_enabled=false
 
[Login] 
login.example.com

Working with iterates in Ansibles. For example in a un-iterates codes below

- name: Ensure the HTTP can pass the firewall 
      firewalld: 
        name: http 
        state: enabled 
        permament: True
        immediate: True
    - name: Ensure the HTTPS can pass the firewall 
      service: 
        name: https 
        state: enabled 
        enabled: True 
      become: True 

The codes can be shortened with the following with_items

- name: Ensure HTTP and HTTPS can pass the firewall 
      firewalld: 
        service: '{{ item }}'  
        state: enabled 
        permanent: True 
        immediate: True 
      become: True
      with_items:
        - http
        - https

Using nested loops – with_nested

If you need to iterate all elements of a list with all items from other lists. For example, you may want to create multiple folderw in multiple paths

--- 
- hosts: all 
  remote_user: ansible
  vars: 
    users: 
      - alice 
      - bob 
    folders: 
      - mail 
      - public_html 
  tasks: 
    - name: Ensure the users exist 
      user: 
        name: '{{ item }}' 
      become: True 
      with_items: 
        - '{{ users }}' 
    - name: Ensure the folders exist 
      file: 
        path: '/home/{{ item.0 }}/{{ item.1 }}' 
        state: directory 
      become: True 
      with_nested: 
        - '{{ users }}' 
        - '{{ folders }}' 

Fileglobs loop – with_fileglobs

If you want to perform an action on every file present in a certain folder like copying multiples files with similar names from one folder to another, you can do the following

--- 
- hosts: all 
  remote_user: ansible
  tasks: 
    - name: Ensure the folder /tmp/iproute2 is present 
      file: 
        dest: '/tmp/iproute2' 
        state: directory 
      become: True 
    - name: Copy files that start with rt to the tmp folder 
      copy: 
        src: '{{ item }}' 
        dest: '/tmp/iproute2' 
        remote_src: True 
      become: True 
      with_fileglob: 
        - '/etc/iproute2/rt_*'