Variables and Facts

Variables and facts make your Ansible automation dynamic and reusable. Variables let you parameterise playbooks, while facts provide real-time information about your managed nodes.

---

Defining Variables

In a Playbook

---
- name: Deploy application
  hosts: webservers
  vars:
    app_name: myapp
    app_port: 8080
    app_env: production

  tasks:
    - name: Print app info
      debug:
        msg: "Deploying {{ app_name }} on port {{ app_port }} ({{ app_env }})"

In External Files

---
- name: Deploy application
  hosts: webservers
  vars_files:
    - vars/common.yml
    - vars/{{ env }}.yml

At the Command Line

# Single variable
ansible-playbook site.yml -e "app_env=staging"

# Multiple variables
ansible-playbook site.yml -e "app_env=staging app_port=9090"

# Variables from a file
ansible-playbook site.yml -e "@vars/overrides.yml"

---

Variable Precedence

Ansible has a well-defined hierarchy for variable precedence. When the same variable is defined in multiple places, the highest precedence wins:

Priority	Source	Notes
1 (lowest)	Role defaults (defaults/main.yml)	Easily overridden
2	Inventory file or script group vars
3	group_vars/all
4	group_vars/<group>
5	Inventory file or script host vars
6	host_vars/<host>
7	Play vars
8	Play vars_files
9	Play vars_prompt
10	Task vars (in a task block)
11	include_vars
12	set_fact / register
13	Role params
14 (highest)	Extra vars (-e)	Always wins

Tip: Extra vars (-e) from the command line always take the highest precedence --- use them for overriding values at runtime.

---

Ansible Facts

Facts are system properties automatically gathered from managed nodes at the beginning of each play (unless gather_facts: false is set).

Viewing All Facts

ansible webservers -m setup

Common Facts

Fact	Example Value	Description
ansible_hostname	web1	Short hostname
ansible_fqdn	web1.example.com	Fully qualified domain name
ansible_os_family	Debian	OS family (Debian, RedHat, etc.)
ansible_distribution	Ubuntu	Distribution name
ansible_distribution_version	22.04	Distribution version
ansible_default_ipv4.address	192.168.1.10	Default IPv4 address
ansible_memtotal_mb	8192	Total memory in MB
ansible_processor_vcpus	4	Number of vCPUs
ansible_architecture	x86_64	CPU architecture

Using Facts in Tasks

tasks:
  - name: Show OS information
    debug:
      msg: "{{ ansible_distribution }} {{ ansible_distribution_version }} ({{ ansible_os_family }})"

  - name: Set worker processes based on CPU count
    template:
      src: nginx.conf.j2
      dest: /etc/nginx/nginx.conf
    vars:
      worker_processes: "{{ ansible_processor_vcpus }}"

Disabling Fact Gathering