Default value for `hosts: {{ host }}` substitution doesn't work

Archives Ansible Project
1

I try to set default value for hosts field in playbook with Jinja2 filter, but it doesn’t work:

  • hosts: “{{ host | default(localhost) }}”
    tasks:
  • name: show OS version info
    debug: msg=“{{ansible_distribution}} {{ansible_distribution_version}}”

ansible-playbook -i hosts dist.yml

PLAY [{{host | default(localhost)}}] ******************************************

skipping: no hosts matched

But when I execute it with command line parameter, it works ok:

ansible-playbook -i hosts dist.yml --extra-vars ‘host=localhost’

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

…

???

2

Change to default(‘localhost’).

3

Found the reason myself:

  • hosts: “{{ host | default(localhost) }}”

This should be:

  • hosts: “{{ host | default(‘localhost’) }}”

Still would be nice to get more valuable error message. I guess Jinja2 translates bare localhost to variable name, which in turn is translated to empty string, but why the Ansible shows PLAY [{{host | default(localhost)}}] **** and not PLAY **** or PLAY [error] **** ?

4

@Scott, thanks. Trial and error told me that way too.

5

If you are attempting to drive the host spec based on inventory variables, this won’t work.

If you drive it with input from -e, it will.

You can’t use inventory variables to drive the host spec.

6

Why? Isn’t the initialization order sets inventory variables first?

7

This is documented here:

http://docs.ansible.com/playbooks_variables.html#variable-precedence-where-should-i-put-a-variable