I've got a number of ansible playbooks that I come back to from time to time, some have required and optional arguments that I forget about from time to time.

I know there's a list-tags, list-hosts and list-tasks option baked into the ansible-playbook command, there's no list-args, which would be super useful, but maybe it means I'm using ansible wrong?

So what strategies do devops engineers use to manage "api's" for ansible playbooks? Maybe just a recursive grep command to list non-standard args that aren't registered variables like this

grep -or "{{[a-zA-Z_ ]\+}}" roles/.  | grep -v "ansible" | grep -v "item"

only better.

For instance, I've got a program I want to put on a device called "showstopper", but I specify the version with extra_args and if I don't specify the version, it doesn't get installed.

 - name: download showstopper from artifactory
   local_action: get_url url=https://example.net/artifactory/generic-release-local/com/cdw/mans/silo/showstopper/showstopper-{{ showstopper_version }}.noarch.rpm dest=/tmp validate_certs=no
   run_once: true
   when: showstopper_version is defined

 - name: copy showstopper to silo
   copy: src=/tmp/showstopper-{{ showstopper_version }}.noarch.rpm dest=/tmp
   when: showstopper_version is defined

 - name: Install showstopper
   yum: name=/tmp/showstopper-{{ showstopper_version }}.noarch.rpm state=present
    - start cron
   when: showstopper_version is defined

This works good when I run it the way I intended to run it, but in 2 months when I want to run it on another machine, I forgot to specify showstopper_version and the last few machines I've built went out without that configured on it.

2 Answers 2


If an extra variable is truly required, you can add assert statements at the top of the role to stop it from executing if they're not defined:

┌─[jamesph@geror] - [~/temp] - [Sat Jan 13, 09:40]
└─[$]> cat assert.yml
- hosts: localhost
    foo: False
    - assert:
          - "foo is defined"
          - "bar is defined"
┌─[jamesph@geror] - [~/temp] - [Sat Jan 13, 09:40]
└─[$]> ansible-playbook assert.yml
 [WARNING]: Unable to parse /etc/ansible/hosts as an inventory source

 [WARNING]: No inventory was parsed, only implicit localhost is available

 [WARNING]: Could not match supplied host pattern, ignoring: all

 [WARNING]: provided hosts list is empty, only localhost is available

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

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

TASK [assert] ****************************************************************************************
fatal: [localhost]: FAILED! => {
    "assertion": "bar is defined",
    "changed": false,
    "evaluated_to": false
    to retry, use: --limit @/Users/jamesph/temp/assert.retry

PLAY RECAP *******************************************************************************************
localhost                  : ok=1    changed=0    unreachable=0    failed=1

some have required and optional arguments that I forget about from time to time


Ok, so if you are writing a redistributable role with reasonable defaults, put those in the roles/x/defaults/main.yml file. This means the role will bring along a default value but ANYTHING in Ansible will override it. It’s just a default. That’s why it says “defaults” :) See Roles for more info about this:

# file: roles/x/defaults/main.yml
# if not overridden in inventory or as a parameter, this is the value that will be used
http_port: 80

If you are writing a role and want to ensure the value in the role is absolutely used in that role, and is not going to be overridden by inventory, you should put it in roles/x/vars/main.yml like so, and inventory values cannot override it. -e however, still will:

In summary, always set reasonable defaults, e.g. a software version that exists instead of using a non-existing one or empty variable and if there is a constant, put it in the vars directory.

There is a number of galaxy playbooks that could be checked:

  • Ok, then it's probably an ansible-smell to use "When" with extra_args. There's some things that I only want to do when I do specify those extra args and I don't want to do them by default. I guess either way it helps to have defaults and just don't do those things when the value is the default, that way all I need to do is cat out my default yamls
    – Peter Turner
    Dec 27, 2017 at 22:14
  • Could you add the code code snippet, e.g. the exact when statement? Could you explain it more functionally, e.g. if system ubuntu and this version then this and otherwise this.
    – 030
    Dec 27, 2017 at 22:19
  • I added code, but I think you hit the nail on he head with specifying default software versions, that'd saved my butt.
    – Peter Turner
    Dec 27, 2017 at 23:11

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