Gathering ansible facts

Gathering facts means, that ansible connects to all hosts of the play and collects information about the host. This information is stored in the variable ansible_facts. This variable is a dictionary and contains information about the host, like the operating system, the hostname, the IP address, the CPU architecture, and so on.

Gathered facts can be used later in the playbook. For example you can make config changes depending on the operating system of the host.

Showing gathered facts with the debug module

gather-facts.yml

- name: "My play"
  hosts: localhost
  tasks:
    - name: "Show facts"
      debug: 
        var: ansible_facts

Running the playbook to gather facts:

ansible-playbook gather-facts.yml

Resulting output:

PLAY [My play] *****************************************************************

TASK [Gathering Facts] *********************************************************
ok: [localhost]

TASK [Show facts] **************************************************************
ok: [localhost] => {
    "ansible_facts": {
        "all_ipv4_addresses": [
            "10.0.0.1"
        ],
        "all_ipv6_addresses": [
            "fe80::215:251:2131:531"
        ],
        "ansible_local": {},
        "apparmor": {
            "status": "disabled"
        },
        "architecture": "x86_64",
        "bios_date": "NA",
        "bios_vendor": "NA",
        "bios_version": "NA",
        "board_asset_tag": "NA",
        ...

It is recommended to disable facts gathering, if you don't need the facts. This improves the performance of the playbook massively.

You can manually disable facts gathering with the gather_facts option:

- name: "My play"
  hosts: localhost
  gather_facts: false
  tasks:
    - name: "Show facts"
      debug: 
        var: ansible_facts

Reference

Ansible docs - gather_facts module