Ansible troubleshooting - undefined variable

---
- name: debug module demo
  hosts: all
  tasks:
    - name: debug message
      ansible.builtin.debug:
        msg: "{{ fruit }}"

$ ansible-playbook troubleshooting/undefinedvariable_error.yml

PLAY [file module demo] ***************************************************************************

TASK [Gathering Facts] ****************************************************************************
ok: [demo.example.com]

TASK [debug message] ******************************************************************************
fatal: [demo.example.com]: FAILED! => {"msg": "The task includes an option with an undefined variable. The error was: 'fruit' is undefined\n\nThe error appears to be in '/Users/lberton/prj/github/ansible-pilot/troubleshooting/undefinedvariable_error.yml': line 5, column 7, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n  tasks:\n    - name: debug message\n      ^ here\n"}

PLAY RECAP ****************************************************************************************
demo.example.com           : ok=1    changed=0    unreachable=0    failed=1    skipped=0    rescued=0    ignored=0

---
- name: debug module demo
  hosts: all
  vars:
    fruit: "apple"
  tasks:
    - name: debug message
      ansible.builtin.debug:
        msg: "{{ fruit }}"

$ ansible-playbook troubleshooting/undefinedvariable_fix.yml

PLAY [debug module demo] **************************************************************************

TASK [Gathering Facts] ****************************************************************************
ok: [demo.example.com]

TASK [debug message] ******************************************************************************
ok: [demo.example.com] => {
"msg": "apple"
}

PLAY RECAP ****************************************************************************************
demo.example.com           : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0