Discovering extra args needed for running ansible playbooks

Question

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
   notify:
    - 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.

Answer 1

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]
└─[$]> cat assert.yml
- hosts: localhost
  vars:
    foo: False
  tasks:
    - assert:
        that:
          - "foo is defined"
          - "bar is defined"
┌─[jamesph@geror] - [~/temp] - [Sat Jan 13, 09:40]
└─[$]> 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

Answer 2

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

http://docs.ansible.com/ansible/latest/playbooks_variables.html#variables-defined-in-inventory

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:

• https://github.com/geerlingguy/ansible-role-nginx
• https://github.com/shelleg/ansible-role-gradle
• https://galaxy.ansible.com/030/firefox/