with_items task and when: statement

[Julien Tognazzi]

What is the proper way to skip a with_items tasks if the with_items variable is undefined ?

I'll try to explain my use case:

I have some variable defined via the group_vars 

And I want to do loop over this variable only if it is defined.

Before ansible 2 it worked without problem

with a playbook like 

---
- hosts: localhost

  tasks:
  - name: "some loop"
    debug: var=item
    with_items:
      - "{{ my_var}}"
    when: my_var is defined
   

If my_var is not defined for the current host, the task is skipped without error or warning.

But with ansible2 I know have a warning.

[DEPRECATION WARNING]: Skipping task due to undefined Error, in the future this will be a fatal error.. This feature will be removed in a future release.

My error is that the when statement is evaluated for each element in the loop...

But then my question is how should I do to have the tasks skipped it the variable is undefined ?

a workaround to have the same behaviour than ansible 1.x is to use the default filter like this

---
- hosts: localhost

  tasks:
  - name: "some loop"
    debug: var=item
    with_items:
      - "{{ my_var|default({}) }}"
    when: item is defined

Do you have some other suggestion ?

thanks for your help.

Julien.

[Matt Martz]

The correct way is to just drop the `when` statement and rely on the `|default` filter:

  tasks:

  - name: "some loop"

    debug: var=item

    with_items:

      - "{{ my_var|default([]) }}"

`when` statements are evaluated for every iteration of the loop, not before the loop.  So they are evaluated after ansible attempts to start looping.

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Matt Martz
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sivel.net

[Josh Smift]

The other thing you could do is define an empty value in a role default,
if you're in a role. (There doesn't seem to be a way to do that if you're
not in a role, i.e. to define a playbook default that can be overridden by
group or host variables, at least not that I see in the precedence list at
https://docs.ansible.com/ansible/playbooks_variables.html#variable-precedence-where-should-i-put-a-variable .)

-Josh (j...@care.com)

(apologies for the automatic corporate disclaimer that follows)




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