playbook-pass-extra-vars.yml

# Example of overriding boolean variable using extra-vars
# Boolean MUST be passed as json
# because key/value pair gets interpreted as string that always evaluates to true
#
# blog: https://fabianlee.org/2021/07/28/ansible-overriding-boolean-values-using-extra-vars-at-runtime/
#
# will correctly say myflag is true, because that is the default
#   ansible-playbook playbook-pass-extra-vars.yml
#
# will incorrectly say myflag is true
#   ansible-playbook playbook-pass-extra-vars.yml --extra-vars "myflag=false"
#
# will correctly say myflag is false
#   ansible-playbook playbook-pass-extra-vars.yml --extra-vars '{ "myflag": false }'
---
- hosts: localhost
  connection: local
  become: no
  gather_facts: no

  # false by default, override with json
  vars:
    myflag: true

  tasks:

    - debug:
        msg: "myflag is true."
      when: myflag

    - debug:
        msg: "myflag is false. You must have used a boolean sent as json or empty value"
      when: not myflag

    - debug:
        msg: "myflag is false when using explicit boolean conversion"
      when: not myflag|bool