Why Ansible facts not available in Roles section?

Question

Question

Why Ansible facts such as ansible_distribution are not available in Roles section?

---
- name: Test
  hosts: all
  tasks:
    - name: debug
      debug:
        msg: "{{ ansible_distribution }}" <----- Works

  roles:
    - "{{ ansible_distribution }}/somerole" <---- ERROR! 'ansible_distribution' is undefined

ansible.cfg

[defaults]
error_on_undefined_vars = True

Answer 1

Why Ansible facts such as ansible_distribution are not available in Roles section?

Because roles dictionary in a play is parsed before executing the setup task which gathers facts.

That said, according to common sense, you should be able to use include_role module in your tasks, but using facts for role names is not possible there either (similarly to this problem, but you can use a workaround I suggested there, i.e. include a role with a static name and use when conditional to control which one).

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Generally, referring to your example, roles were designed to provide an abstraction level and are supposed to handle architectural differences inside them, not outside.