Each role can have it's own unique set of variables, and there are numerous ways to define the variables that will be used by a role. This is in the order of precedence, top down, where the option higher in the list takes precedence.

• Define variables using the --extra-vars command line option
• Define variables using the vars plugin
• Define variables in vars/main.yml
• Define variables in defaults/main.yml

For example, let's say you have a role named "foo" that contain main.yml.

/usr/local/ansible/roles/foo/tasks/main.yml

Let's say main.yml contains the following.

- name: output the bar variable
  debug:
    var: bar

vars option

Let's say your testing.yml playbook uses the foo role. Here is how you can assign a value of "Hello World" to the bar variable using the vars option.

---
- hosts: localhost
  roles:
  - role: foo
    vars:
      bar: "Hello World"
...

Or like this.

---
- hosts: localhost
  roles:
  - { role: foo, vars: { bar: "Hello World" } }
...

Invoking testing.yml should return the following.

TASK [foo: output the bar variable] 
ok: [localhost] => {
    "bar": "Hello World"
}

vars and defaults directories

Or, variables can be put in the roles/foo/defaults/main.yml file or the roles/foo/vars/main.yml file, like this.

bar: "Hello World"

As long as you are not using the --extra-vars command line option and your testing.yml does not contain the vars option, Ansible will next check roles/foo/vars/main.yml file for the bar variable and then roles/foo/defaults/main.yml.

---
- hosts: localhost
  roles:
  - role: foo
...