what is the purpose of main.yml file in vars folder in ansible role?

Q: What is the purpose of main.yml file in vars folder in ansible role?

A: Main reason is to customize role's default variables.

The variables defined in role/vars/main.yml override all variables defined in roles defaults, inventories, group_vars, host_vars, and all variables defined in the play before the role was included in the play. See Variable precedence: Where should I put a variable? for details.

For example, let's create a playbook

shell> cat playbook.yml 
- hosts: localhost
  vars:
    test_var: test_var defined in the playbook vars
  roles:
    - role1

and let's create a role with empty roles/role1/vars/main.yml and simple debug task in roles/role1/tasks/main.yml

shell> cat roles/role1/tasks/main.yml
- debug:
    var: test_var

shell> cat roles/role1/vars/main.yml 
---
# vars file for role1

The play will display the variable defined in the playbooks' vars

shell> ansible-playbook test-14.yml 
  ...
  test_var: test_var defined in the playbook vars

Now, define the variable test_var in role's role1/vars/main.yml

shell> cat roles/role1/vars/main.yml 
---
# vars file for role1
test_var: test_var defined in the role vars

The variable defined in the role's vars overridden the variable defined in the playbook's vars.

shell> ansible-playbook playbook.yml 
  ...
  test_var: test_var defined in the role vars

Notes:

• Do not put roles' vars/main.yml into the Ansible Galaxy git. This will preserve local customizations from updates and upgrades.

#file: copy-static.yml

• name: Copy a file copy: src=examplefile1.txt dest=/home/user/example.txt

#file: copy-template.yml

• name: sample template - x template: src: templateexample.txt.j2 dest: /home/user/newexample.txt with_items: var_x

#file: ngnix.yml

- name: install nginx
 apt: name=nginx update_cache=yes state=latest
- name: displaying message
  debug: msg="yayy!! nginx installed"
  

#file: mainplaybook.yml

• hosts: localhost connection: local become: yes become_method: sudo roles:
  • fresco_roles/sample_role

#file: tasks/main.yml

• include: nginx.yml
• include: copy-static.yml
• include: copy-template.yml

#file: hosts [localhost] localhost

#file: vars/main.yml

project_files: files: - src: "examplefile1.txt" dst: "~/examplefile1.txt" mode: '0755' force: false templates: - src: "templateexample.txt.j2" dst: "~/templateexample.txt" mode: '0755' force: false var_x:

• 'variable x' var_y:
• 'variable y'