Ansible with_subelements

Question

I am having a hard time understanding the logic of ansible with_subelements syntax, what exactly does with_subelements do? i took a look at ansible documentation on with_subelements here https://docs.ansible.com/ansible/latest/user_guide/playbooks_loops.html#with-subelements and was not very helpful. I also saw a playbook with with_subelements example on a blog

---
- hosts: cent
  vars:
    users:
     - name: jagadish
       comments:
         - 'Jagadish is Good'

     - name: srini
       comments:
         - 'Srini is Bad' 

  tasks:
   - name: User Creation
     shell: useradd -c "{{ item.1 }}" "{{ item.0.name }}"
     with_subelements:
         - users
         - comments

what do item.1 and item.0 refer to?

question from:https://stackoverflow.com/questions/41908715/ansible-with-subelements

Answer 1

This is really bad example of how subelements lookup works. (And has old, unsupported, syntax as well).

Look at this one:

---
- hosts: localhost
  gather_facts: no
  vars:
    families:
      - surname: Smith
        children:
          - name: Mike
            age: 4
          - name: Kate
            age: 7
      - surname: Sanders
        children:
          - name: Pete
            age: 12
          - name: Sara
            age: 17

  tasks:
    - name: List children
      debug:
        msg: "Family={{ item.0.surname }} Child={{ item.1.name }} Age={{ item.1.age }}"
      with_subelements:
        - "{{ families }}"
        - children

Task List children is like a nested loop over families list (outer loop) and over children subelement in each family (inner loop).
So you should provide a list of dicts as first argument to subelements and name of subelement you want to iterate inside each outer item.

This way item.0 (family in my example) is an outer item and item.1 (child in my example) is an inner item.

In Ansible docs example subelements is used to loop over users (outer) and add several public keys (inner).