ansible: correct way to check a list of variables has been set?

Question

I\'m trying to use when: item is undefined in Ansible 2.5 to check if a list of variables have been set, as below:

- hosts: all
  tasks:
    - n         


        

Answer 1

Using the vars structure:

- name: validate some variables
  fail:
    msg: "Required variable {{item}} has not been provided"
  when: vars[item] is undefined
  loop:
    - v1
    - v2

Or, in Ansible 2.5, with the new vars lookup plugin:

- name: validate some variables
  debug:
  when: lookup('vars', item) is undefined
  loop:
    - v1
    - v2

Although not with the error message you specified, but a default error message for a lookup plugin.

^{The module won't even be executed, so you can use whatever ー I replaced fail with debug in the example above.}