Eu tenho dois manuais que são lançados contra um host remoto (10.233.84.58) Quando lançado autônomo (ansible-playbook -i inventory.txt playbook.yml) eles funcionam bem.

O primeiro manual inclui o segundo, que é idêntico, exceto obviamente peloinclude:

---
- hosts: all
  tasks:
    - debug: msg="hello form playbook1"
    # up to now the content is identical between playbook1.yaml and playbook2.yaml
    # without the next line the playbook runs fine
    - include: playbook2.yml

Quando eu corroplaybook1.yml:

# ansible-playbook -i inventory.txt playbook1.yml                                                                (master✱)

PLAY [all] *********************************************************************

TASK [setup] *******************************************************************
ok: [10.233.84.58]

TASK [debug] *******************************************************************
ok: [10.233.84.58] => {
    "msg": "hello form playbook1"
}

TASK [include] *****************************************************************
fatal: [10.233.84.58]: FAILED! => {"failed": true, "reason": "no action detected in task. This often indicates a misspelled module name, or incorrect module path.\n\nThe error appears to have been in '/root/tests/playbook2.yml': line 2, column 3, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n---\n- hosts: all\n  ^ here\n\n\nThe error appears to have been in '/root/tests/playbook2.yml': line 2, column 3, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n---\n- hosts: all\n  ^ here\n"}

NO MORE HOSTS LEFT *************************************************************
        to retry, use: --limit @playbook1.retry

PLAY RECAP *********************************************************************
10.233.84.58               : ok=2    changed=0    unreachable=0    failed=1

Extraí o "motivo" da mensagem de erro acima e o tornei mais legível:

no action detected in task. This often indicates a misspelled module name, or incorrect module path.

The error appears to have been in '/root/tests/playbook2.yml': line 2, column 3, but may
be elsewhere in the file depending on the exact syntax problem.

The offending line appears to be:

---
- hosts: all
  ^ here

Como um manual de inclusão deve ser diferente de um manual independente?