Second role execution overrides default parameter value

Question

I have an ansible role that defines two parameters and a default for the second one.

roles/upstream/tasks/main.yml:

---
- debug:
    msg: "Parameter in upstream is {{param}} and param2 is {{param2}}"

roles/upstream/defaults/main.yml:

---
param2: []

And then this exemplary play:

---
- name: test
  hosts: localhost
  roles:
    - role: upstream
      vars:
        param: 21
    - role: upstream
      vars:
        param: 42
        param2: test

When I execute this, I see the following:

TASK [Gathering Facts] **********************************************************************************
ok: [localhost]

TASK [upstream : debug] *********************************************************************************
ok: [localhost] => {
    "msg": "Parameter in upstream is 21 and param2 is test"
}

TASK [upstream : debug] *********************************************************************************
ok: [localhost] => {
    "msg": "Parameter in upstream is 42 and param2 is test"
}

What is the rationale that the second call to the role also overrides the default for param2 for the other call and how to avoid this?

@techraf thanks, that prevents this problem, but also makes variables inaccessible to other roles... hmmm... — languitar, Aug 30 '18 at 19:27
Because roles in Ansible were originally just an organisational feature. Variables can be play-scoped, or task-scoped, but not role-scoped (there are also extravars, different story). With `vars` inside `roles` section of a play, they are first read as play variables (last value wins), then for each task inside a role the `vars` from that role declaration is applied. — techraf, Aug 30 '18 at 19:59
@techraf I see the technical reasons, but that is extremely counter-intuitive and I see no way to work around that? — languitar, Aug 31 '18 at 08:57

score 1 · Accepted Answer · answered Sep 11 '18 at 20:31

The behaviour you observe is expected.

Roles in Ansible were originally just an organisational feature. Variables can be play-scoped, or task-scoped, but not role-scoped (there are also extravars, facts, magic variables behaving differently, but not relevant here).

With vars inside the roles section of a play, they are first read as play variables (last value defined wins), then for each task inside a role the vars from that role declaration is applied.

To avoid the problem, you should use use include_role or import_role module in tasks (or pre_tasks).

Then, per your additional requirement in the comment:

[this] makes variables inaccessible to other roles...

You can make the defaults and vars defined in roles visible outside of the roles by setting a new parameter public in Ansible 2.7 (in development as of writing this answer).

Final solution:

- hosts: localhost
  connection: local
  gather_facts: no

  tasks:
    - include_role:
        name: upstream
        public: true
      vars:
        param: 21

    - debug:
        var: param2

    - include_role:
        name: upstream
      vars:
        param: 42
        param2: test

Thanks. Apart from the new `public` feature, this the approach I came up with already. — languitar, Sep 12 '18 at 09:05

Second role execution overrides default parameter value

1 Answers1