Where does multi-role variable goes in Ansible?

Question

There are multiple kind of variables in Ansible. And I find it overwhelming to wrap my head around them. Some of them are:

• The one we can write in roles//vars/main.yml
• The one we can write in the tasks file itself.
• Then there are group_vars.
• Then we have host_vars.
• There are also vars files.

My use case is... I have three roles. Namely nginx, jenkins and certbot. Thing common in all of them is the domain name. I decided to use a variable named {{ fqdn }} in all of those for sake of refactoring.

I am not able to decide on which version to use.

What I want is... ability to input the fqdn from command line when playbook is running. There should be default value which I can put somewhere in the repo.

Answer 1

See Variable precedence: Where should I put a variable?. You can see that the role's defaults represent the lowest precedence for variables and the extra variables, declared on the command-line, override everything. There are a plethora of options between these two options.

For testing, create the roles and the playbook below. For example

shell> tree roles/
roles/
├── certbot
│   ├── defaults
│   │   └── main.yml
│   └── tasks
│       └── main.yml
├── jenkins
│   ├── defaults
│   │   └── main.yml
│   └── tasks
│       └── main.yml
└── nginx
    ├── defaults
    │   └── main.yml
    └── tasks
        └── main.yml

9 directories, 6 files

There are only two files in each role. The files are identical in all roles

shell> cat roles/certbot/defaults/main.yml 
fqdn: "{{ fqdn_default|default('srv.example.com') }}"

shell> cat roles/certbot/tasks/main.yml 
- debug:
    var: fqdn

Then, the playbook below

shell> cat playbook.yml
- hosts: localhost
  roles:
    - certbot
    - jenkins
    - nginx

gives as expected

shell> ansible-playbook playbook.yml 

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

TASK [certbot : debug] ***************************************************
ok: [localhost] => 
  fqdn: srv.example.com

TASK [jenkins : debug] ***************************************************
ok: [localhost] => 
  fqdn: srv.example.com

TASK [nginx : debug] *****************************************************
ok: [localhost] => 
  fqdn: srv.example.com

In this example, the default values of fqdn in all roles are the same. Of course, you can declare different default values for each role if you want to.

---

You can declare the variable on the command-line

shell> ansible-playbook playbook.yml -e fqdn=www.example.com

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

TASK [certbot : debug] ***************************************************
ok: [localhost] => 
  fqdn: www.example.com

TASK [jenkins : debug] ***************************************************
ok: [localhost] => 
  fqdn: www.example.com

TASK [nginx : debug] *****************************************************
ok: [localhost] => 
  fqdn: www.example.com

---

Moreover, in this example, you can also change the default value, e.g. in the group_vars

shell> cat group_vars/all.yml 
fqdn_default: default.example.com

Then the playbook will use the value of fqdn_default

shell> ansible-playbook playbook.yml 

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

TASK [certbot : debug] ****************************************************
ok: [localhost] => 
  fqdn: default.example.com

TASK [jenkins : debug] ****************************************************
ok: [localhost] => 
  fqdn: default.example.com

TASK [nginx : debug] ******************************************************
ok: [localhost] => 
  fqdn: default.example.com

---

Use vars_prompts if you want to input the fqdn from the command line when the playbook is running. e.g.

shell> cat playbook.yml
- hosts: localhost
  vars_prompt:
    - name: fqdn
      prompt: What is the fqdn?
      private: no
  roles:
    - certbot
    - jenkins
    - nginx

shell> ansible-playbook playbook.yml
What is the fqdn?: ww9.example.com

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

TASK [certbot : debug] ************************************************
ok: [localhost] => 
  fqdn: ww9.example.com

TASK [jenkins : debug] *************************************************
ok: [localhost] => 
  fqdn: ww9.example.com

TASK [nginx : debug] ***************************************************
ok: [localhost] => 
  fqdn: ww9.example.com

Quoting from the Note: "Prompts for individual vars_prompt variables will be skipped for any variable that is already defined through the command line --extra-vars option,..."