Ansible skipの場合 registerに格納しないようにする

まず事象として

タスクがskipされたときでもregisterにはその旨が格納されてしまう。

- hosts: localhost
  tasks:
    - debug:
        msg: "TRUE"
      register: true_register
      when: true
    - debug:
        var: true_register

    - debug:
        msg: "FALSE"
      register: false_register
      when: false
    - debug:
        var: false_register

$ docker compose run ansible ansible-playbook playbook.yaml
[WARNING]: No inventory was parsed, only implicit localhost is available
[WARNING]: provided hosts list is empty, only localhost is available. Note that the implicit localhost does not match 'all'

PLAY [localhost] *************************************************************************************************************************************************************

TASK [Gathering Facts] *******************************************************************************************************************************************************
ok: [localhost]

TASK [debug] *****************************************************************************************************************************************************************
ok: [localhost] => {
    "msg": "TRUE"
}

TASK [debug] *****************************************************************************************************************************************************************
ok: [localhost] => {
    "true_register": {
        "changed": false,
        "failed": false,
        "msg": "TRUE"
    }
}

TASK [debug] *****************************************************************************************************************************************************************
skipping: [localhost]

TASK [debug] *****************************************************************************************************************************************************************
ok: [localhost] => {
    "false_register": {
        "changed": false,
        "skip_reason": "Conditional result was False",
        "skipped": true
    }
}

PLAY RECAP *******************************************************************************************************************************************************************
localhost                  : ok=4    changed=0    unreachable=0    failed=0    skipped=1    rescued=0    ignored=0

対策として

公式ドキュメントにも書いてあるとおり、タグで回避しましょう。

If a task fails or is skipped, Ansible still registers a variable with a failure or skipped status, unless the task is skipped based on tags. See Tags for information on adding and using tags.

https://docs.ansible.com/ansible/latest/user_guide/playbooks_variables.html#registering-variables

- hosts: localhost
  tasks:
    - block:
      - debug:
          msg: "TRUE"
        register: true_register
      - debug:
          var: true_register
      tags:
      - true_flag

    - block:
      - debug:
          msg: "FALSE"
        register: false_register
      - debug:
          var: false_register
      tags:
      - false_flag

$ docker compose run ansible ansible-playbook playbook.yaml --tags=true_flag
[WARNING]: No inventory was parsed, only implicit localhost is available
[WARNING]: provided hosts list is empty, only localhost is available. Note that the implicit localhost does not match 'all'

PLAY [localhost] *************************************************************************************************************************************************************

TASK [Gathering Facts] *******************************************************************************************************************************************************
ok: [localhost]

TASK [debug] *****************************************************************************************************************************************************************
ok: [localhost] => {
    "msg": "TRUE"
}

TASK [debug] *****************************************************************************************************************************************************************
ok: [localhost] => {
    "true_register": {
        "changed": false,
        "failed": false,
        "msg": "TRUE"
    }
}

PLAY RECAP *******************************************************************************************************************************************************************
localhost                  : ok=3    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0