Define Ansible variable in a role with OS specific default which can be easily overridden

Question

I'm writing an Ansible role that is usable on different Linux OS families and has a different default value for variables per OS family.

At first, I thought this would be easy to set up using an include vars task in the role, such as:

- name: Gather OS family variables
  include_vars: "{{ ansible_os_family|lower }}.yml"

with

my_role_variable: "Here is the default for Enterprise Linux"

in myrole/vars/redhat.yml

my_role_variable: "Here is the default for Debian Linux"

in myrole/vars/debian.yml

However, in my case it's very important that a playbook using the role be able to easily override the default values.

So, I'm trying to figure out a way to set up a different default value for the variable per OS family as described above, but I want the variables be role default vars instead of role include vars. Is there a way to do this?

Answer 1

Use a ternary operator:

- name: Gather OS family variables
  include_vars: "{{ (override_os_family is defined) | ternary(override_os_family,ansible_os_family) | lower }}.yml"

This way, if the variable override_os_family is defined, your expression will have its value, if not, it will use the value of ansible_os_family.

---

Example:

---
- hosts: localhost
  connection: local
  tasks:   
    - debug: msg="{{ (override_os_family is defined) | ternary(override_os_family,ansible_os_family) | lower }}.yml"

- hosts: localhost
  connection: local
  vars:
    override_os_family: Lamarck
  tasks:   
    - debug: msg="{{ (override_os_family is defined) | ternary(override_os_family,ansible_os_family) | lower }}.yml"

Result (excerpt):

...

TASK [debug] *******************************************************************
ok: [localhost] => {
    "msg": "darwin.yml"
}

...

TASK [debug] *******************************************************************
ok: [localhost] => {
    "msg": "lamarck.yml"

Answer 2

what about having something like the following in your defaults/main.yml file

my_role_variable_default: "global default"
my_role_variable_redhat: "redhat specific default"
my_role_variable: "{{ lookup('vars', 'my_role_variable_'+ansible_os_family|lower, default=my_role_variable_default) }}"