Ansible role depend on other roles

Question

I have a role, foo that installs a file {{ foo_path }} that's defined in roles/defaults/main.yml.

I have a second role, bar that depends on that file being there. I could put foo in the roles/meta/main.yml dependencies but then it will run the entire role which is not ideal. I could potentially tag the task in the role that creates the file, but that's not really scalable, and introduces problems when I'm not the owner of that role's code.

I could just assert that the file is there, but the problem is that I don't know where "there" is.

How can I load the foo_path var from a different role without the overhead of running the play?

Answer 1

Given the foo defaults

shell> cat roles/foo/defaults/main.yml 
foo_path: /tmp/test.txt

There are more options:

1. Include the foo defaults into a dictionary and get the variable foo_path

shell> cat pb_bar.yml
- hosts: localhost
  pre_tasks:
    - include_vars:
        file: roles/foo/defaults/main.yml
        name: foo_defaults
    - debug:
        var: foo_defaults.foo_path
      when: debug|d(false)|bool
    - set_fact:
        foo_path: "{{ foo_defaults.foo_path }}"
  roles:
    - bar

Use the variable in the role bar

shell> cat roles/bar/tasks/main.yml
- stat:
    path: "{{ foo_path }}"
  register: foo_path_st
- debug:
    var: foo_path_st
  when: debug|d(false)|bool
- assert:
    that: foo_path_st.stat.exists

gives

shell> ansible-playbook pb_bar.yml -e debug=true

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

TASK [include_vars] **************************************************************************
ok: [localhost]

TASK [debug] *********************************************************************************
ok: [localhost] => 
  foo_defaults.foo_path: /tmp/test.txt

TASK [set_fact] ******************************************************************************
ok: [localhost]

TASK [Assert foo_path] ***********************************************************************
skipping: [localhost]

TASK [bar : stat] ****************************************************************************
ok: [localhost]

TASK [bar : debug] ***************************************************************************
ok: [localhost] => 
  foo_path_st:
    ansible_facts:
      discovered_interpreter_python: /usr/bin/python3
    changed: false
    failed: false
    stat:
      ...
      exists: true
      ...
      path: /tmp/test.txt

TASK [bar : assert] **************************************************************************
ok: [localhost] => changed=false 
  msg: All assertions passed

PLAY RECAP ***********************************************************************************
localhost: ok=6    changed=0    unreachable=0    failed=0    skipped=1    rescued=0    ignored=0

---

2. Structure the roles' tasks

shell> tree roles
roles
├── bar
│   └── tasks
│       └── main.yml
└── foo
    ├── defaults
    │   └── main.yml
    └── tasks
        ├── assert_foo_path.yml
        ├── install_foo_path.yml
        └── main.yml

5 directories, 5 files

shell> cat roles/foo/tasks/assert_foo_path.yml 
- stat:
    path: "{{ foo_path }}"
  register: foo_path_st
- debug:
    var: foo_path_st
  when: debug|d(false)|bool
- assert:
    that: foo_path_st.stat.exists

shell> cat roles/foo/tasks/install_foo_path.yml 
- file:
    path: "{{ foo_path }}"
    state: touch

shell> cat roles/foo/tasks/main.yml 
- name: Install foo_path
  include_tasks: install_foo_path.yml
- name: Assert foo_path
  include_tasks: assert_foo_path.yml

and use the module include_role

shell> cat roles/bar/tasks/main.yml 
- name: Assert foo_path
  include_role:
    name: foo
    tasks_from: assert_foo_path.yml

Create playbooks for testing

shell> cat pb_foo.yml 
- hosts: localhost
  roles:
    - foo

shell> cat pb_bar.yml 
- hosts: localhost
  roles:
    - bar

The play will fail if the file is missing

shell> ansible-playbook pb_bar.yml -e debug=false

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

TASK [Assert foo_path] ***********************************************************************

TASK [foo : stat] ****************************************************************************
ok: [localhost]

TASK [foo : debug] ***************************************************************************
skipping: [localhost]

TASK [foo : assert] **************************************************************************
fatal: [localhost]: FAILED! => changed=false 
  assertion: foo_path_st.stat.exists
  evaluated_to: false
  msg: Assertion failed

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

Create the file

shell> ansible-playbook pb_foo.yml -e debug=false

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

TASK [foo : Install foo_path] ****************************************************************
included: /export/scratch/tmp7/test-321/roles/foo/tasks/install_foo_path.yml for localhost

TASK [foo : file] ****************************************************************************
changed: [localhost]

TASK [foo : Assert foo_path] *****************************************************************
included: /export/scratch/tmp7/test-321/roles/foo/tasks/assert_foo_path.yml for localhost

TASK [foo : stat] ****************************************************************************
ok: [localhost]

TASK [foo : debug] ***************************************************************************
skipping: [localhost]

TASK [foo : assert] **************************************************************************
ok: [localhost] => changed=false 
  msg: All assertions passed

PLAY RECAP ***********************************************************************************
localhost: ok=5    changed=1    unreachable=0    failed=0    skipped=1    rescued=0    ignored=0

The assert task will succeed now

TASK [foo : assert] **************************************************************************
ok: [localhost] => changed=false 
  msg: All assertions passed