How to gather ansible_facts inside of a role only when needed?

Question

I have this example role where I install some packages based on the OS and package manager:

# THIS IS IN tasks/main.yml
- name: Ensure archlinux-keyring is updated
  community.general.pacman:
    name: archlinux-keyring
    state: latest
    update_cache: yes
  when: ansible_pkg_mgr == "pacman"

If this role is run as part of a playbook, Ansible will gather the facts and everything is just fine. However, if I run it as a standalone role:

ansible localhost -m include_role -a name=examplerole

I get this error

localhost | FAILED! => {
    "msg": "The conditional check 'ansible_pkg_mgr == \"pacman\"' failed. The error was: error while evaluating conditional (ansible_pkg_mgr == \"pacman\"): 'ansible_pkg_mgr' is undefined

I know I can force Ansible to gather these facts inside the role, but gathering facts over and over again will be super slow (as this is a recurring problem I have with several roles, and I can't always include them in a playbook, and also, if they ARE in a playbook, this isn't needed).

Is there any way to check if facts were already gathered, and gather them inside of the role only when needed?

Answer 1

Regarding

...Is there any way to check if facts were already gathered ... gather them inside of the role only when needed?

and if you like to gather facts based on conditionals only, you may have a look into the following example

- hosts: localhost
  become: false

  gather_facts: false

  tasks:

  - name: Show Gathered Facts
    debug:
      msg: "{{ hostvars['localhost'].ansible_facts }}"

  - name: Gather date and time only
    setup:
      gather_subset:
        - "date_time"
        - "!min"
    when: ansible_date_time is not defined

  - name: Show Gathered Facts
    debug:
      msg: "{{ ansible_facts }}"

which is gathering date and time only and if not defined before.

This means, regarding

gathering facts over and over again will be super slow

it is recommended to get familiar with the data structure of the gathered facts and the possible subsets in order to gather only the information which is needed. And as well with Caching facts.

Further Documentation

• setup module – Gathers facts about remote hosts
• What is the exact list of Ansible setup min?