Ansible Playbook variables and facts

Now that you have learned more about Ansible’s directory structure and inventories let us have a look at the variables in Ansible and how Ansible facts can be used to retrieve detailed information of managed hosts. 

In this lesson, you will:

• Learn about variables in Ansible.
• Learn about Ansible facts.

Variables in Ansible

Variables in Ansible are YAML key-value pairs that store data for reuse in playbooks, making them more flexible and customizable. You can define variables in your playbooks, inventory, variable files, or at the command line.

Review the official Ansible documentation for information on variable precedence. 

Declaring variables in playbooks

Variables in playbooks are defined under the vars section in a play and can be used in the specific play they’re declared in.

Let’s add variables to our site.yml playbook:

---
- name: Install and start Apache
  hosts: web
  become: true
  vars:
    package_name: httpd
  tasks:
    - name: Ensure the httpd package is installed
      ansible.builtin.package:
        name: "{{ package_name }}"
        state: present

Ansible playbook variable example.

Using variables in the Inventory

The previous lesson covered adding variables to Ansible inventory groups and hosts. Let’s use an example to illustrate using these variables in a playbook.

---
all:
 children:
   web:
     vars:
       package_name: httpd
     hosts:
       web1:
         ansible_host: 192.168.0.10
       web2:
         ansible_host: web2.example.com
   database:
     hosts:
       db1:
         ansible_user: rhel

Ansible YAML inventory variables example.

---
- name: Install and start Apache
  hosts: web
  become: true
  tasks:
    - name: Ensure the httpd package is installed
      ansible.builtin.package:
        name: "{{ package_name }}"
        state: present

Ansible playbook inventory variables example.

# vars.yml
                                        ---
                                        package_name: httpd

Variable file example.

You can include variable files in your playbook using the vars_files section or the ansible.builtin.include_vars module. 

Let’s use an example to include a variable file in a playbook:

---
- name: Install and start Apache
  hosts: web
  become: true
  vars_files:
    - vars.yml
  tasks:
    - name: Ensure the httpd package is installed
      ansible.builtin.package:
        name: "{{ package_name }}"
        state: present

Ansible playbook variable file example.

Using host_vars and group_vars

Ansible automatically loads variable files into playbooks in the host_vars and group_vars folders based on the host or group name and the associated file name. 

For Ansible to automatically associate the host_vars and group_vars folders, they must be in a specific location relative to your Ansible inventory file or playbook file.

The folders can be adjacent to the inventory file:

project-name/
├── inventory/
│   ├── hosts                 # Custom inventory file
│   ├── group_vars/
│   │   └── web.yml           # Variables for 'web group'
│   └── host_vars/
│       └── web1.yml          # Variables for 'web1 host'
└── site.yml

Ansible inventory folder group_vars and host_vars.

Or the folders can be adjacent to the Ansible playbook:

project-name/
├── inventory                 # Inventory file
├── group_vars/
│   └── web.yml               # Variables for 'web' group
├── host_vars/
│   └── web1.yml            # Variables for 'web1' host
└── site.yml

Ansible playbook adjacent folder group_vars and host_vars.

For example, let’s create a web.yml YAML file in the ./project-name/group_vars/ folder:

# ./project-name/group_vars/web.yml
---
package_name: httpd

Ansible inventory group_vars example.  

---
                - name: Install and start Apache
                  hosts: web
                  become: true
                  vars_files:
                    - vars.yml
                  tasks:
                    - name: Filter and return only selected facts
                      ansible.builtin.setup:
                        filter:
                          - 'os_family'
                          - 'ansible_distribution'
                    - name: Ensure the httpd package is installed
                      ansible.builtin.package:
                        name: "{{ package_name }}"
                        state: present
                      when: ansible_facts['os_family'] == "RedHat"
                

Ansible playbook facts example.