Lesson 4.3: Managing Facts

What Are Ansible Facts?

Ansible facts are system properties and variables automatically collected from managed hosts during playbook execution. These facts provide crucial information about the system’s hardware, network, OS, and other configurations, allowing playbooks to adapt dynamically.

Facts are gathered using the setup module, which runs by default at the beginning of playbook execution unless explicitly disabled.

Using Facts in Playbooks

Facts can be referenced in playbooks using Jinja2 templating syntax :

- name: Display system information
  hosts: all
  tasks:
    - name: Show OS family
      debug:
        msg: "This system runs on {{ ansible_os_family }} OS."

Fact Variable	Description
ansible_facts['fqdn']	Fully Qualified Domain Name (FQDN)
ansible_facts['hostname']	Hostname of the system
ansible_facts['default_ipv4']['address']	Primary IPv4 address
ansible_facts['os_family']	OS family (e.g., RedHat, Debian)
ansible_facts['distribution']	Linux distribution (e.g., Ubuntu, CentOS)
ansible_facts['memtotal_mb']	Total memory in MB
ansible_facts['processor_count']	Number of CPU cores

Facts Used in This Example

In the given example, Ansible facts are used to dynamically generate a /etc/myhosts file for all managed nodes. The key facts used are:

ansible_facts['default_ipv4']['address']
- Retrieves the primary IPv4 address of each host.
- Example: 192.168.208.150 for node1.
ansible_facts['fqdn']
- Returns the Fully Qualified Domain Name (FQDN) of the host.
- Example: node1.example.com (if set).
ansible_facts['hostname']
- Provides the short hostname of the machine.
- Example: node1.

[devops@ansible-server ansible]$ cat hosts.j2 
127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
::1         localhost localhost.localdomain localhost6 localhost6.localdomain6
 
{% for x in groups['all'] %}
{{ hostvars[x]['ansible_facts']['default_ipv4']['address'] }}   {{ hostvars[x]['ansible_facts']['fqdn'] }}  {{ hostvars[x]['ansible_facts']['hostname'] }}
{% endfor %}
[devops@ansible-server ansible]$ 
[devops@ansible-server ansible]$ vim gen_hosts.yml
[devops@ansible-server ansible]$ cat gen_hosts.yml 
- name: Playbook to create hosts file
  hosts: all 
  tasks:
  - name: Template a file to /etc/hosts
    ansible.builtin.template:
      src: /home/devops/ansible/hosts.j2
      dest: /etc/myhosts
[devops@ansible-server ansible]$ ansible-playbook --syntax-check gen_hosts.yml 
 
playbook: gen_hosts.yml
[devops@ansible-server ansible]$ ansible-playbook  gen_hosts.yml

How These Facts Are Used in the Template (hosts.j2): The Jinja2 template iterates over all hosts in the inventory using:

{% for x in groups['all'] %}
{{ hostvars[x]['ansible_facts']['default_ipv4']['address'] }}   {{ hostvars[x]['ansible_facts']['fqdn'] }}  {{ hostvars[x]['ansible_facts']['hostname'] }}
{% endfor %}
This generates a /etc/myhosts file with entries like:

192.168.208.150   node1.example.com  node1
192.168.208.151   node2.example.com  node2
192.168.208.152   node3.example.com  node3
192.168.208.153   node4.example.com  node4

Each line dynamically maps the IP, FQDN, and hostname of every managed node using Ansible facts.

Automating System Information Collection

In this example, Ansible facts are used to generate a hardware report for each managed node, storing details in /root/hw_report.txt. The key facts used are:

ansible_facts['hostname']

Retrieves the short hostname of the machine.
Example: node1.

ansible_facts['memtotal_mb']

Returns the total amount of system memory (RAM) in megabytes.
Example: 3585 MB.

ansible_facts['bios_version']

Provides the BIOS version of the machine.
Example: VMW201.00V.21805430.BA64.2305221830.

How These Facts Are Used in the Template (hwreport.j2):

Inventory Hostname {{ ansible_facts['hostname'] }}
Total Memory in MB {{ ansible_facts['memtotal_mb'] }}
BIOS Version {{ ansible_facts['bios_version'] }}
This generates a report for each node, such as:

Inventory Hostname node1
Total Memory in MB 3585
BIOS Version VMW201.00V.21805430.BA64.2305221830

Each node gets its own report with dynamically collected system information using Ansible facts.

 
[devops@ansible-server ansible]$ vim hwreport.j2
[devops@ansible-server ansible]$ cat hwreport.j2 
Inventory Hostname {{ ansible_facts['hostname'] }}
Total Memory in MB {{ ansible_facts['memtotal_mb'] }}
BIOS Version {{ ansible_facts['bios_version'] }}
 
[devops@ansible-server ansible]$ cat hwreport.yml 
- name: Playbook to create device config file
  hosts: all 
  tasks:
  - name: Template a file to /roor/hw_report.txt
    ansible.builtin.template:
      src: /home/devops/ansible/hwreport.j2
      dest: /root/hw_report.txt
 
 
[devops@ansible-server ansible]$ ansible-playbook hwreport.yml 
 
[devops@ansible-server ansible]$ ansible all -m command -a 'cat /root/hw_report.txt'
node1 | CHANGED | rc=0 >>
Inventory Hostname node1
Total Memory in MB 3585
BIOS Version VMW201.00V.21805430.BA64.2305221830
node3 | CHANGED | rc=0 >>
Inventory Hostname node3
Total Memory in MB 3585
BIOS Version VMW201.00V.21805430.BA64.2305221830
node2 | CHANGED | rc=0 >>
Inventory Hostname node2
Total Memory in MB 3582
BIOS Version VMW201.00V.21805430.BA64.2305221830
node4 | CHANGED | rc=0 >>
Inventory Hostname node4
Total Memory in MB 3585
BIOS Version VMW201.00V.21805430.BA64.2305221830