Harmonize how global variables are shared between roles

[eroussy]

Abstract
All role-specific variables must use the role prefix in Ansible (ex: timemaster_ptp_network_transport for the timemaster role).
We must harmonize how variables shared by multiple roles are handled:

• How they are named
• How they are passed to all the roles that need them

Current status
Shared role variables are named using legacy naming and passed directly to the role without any mention in the role's defaults file, nor any validation in the role.
For example: hostname and cluster_ip_addr are used by the cephadm role, but they are not present in the defaults file, nor do they use the cephadm_ prefix.

Detailed Description
I advise creating one variable per role and passing the global variable to them in the inventory.
For the cephadm role, it would mean:

• Create cephadm_hostname and cephadm_ip_addr.
• Mention them in the role defaults (make them default to null as they are required).
• Write cephadm_hostname: "{{ hostname }}" and cephadm_ip_addr: "{{ cluster_ip_addr }}" in the inventory.

I proposed this approach in #866 for the podman_registry_mirror_url variable.
6d725a9

The main drawback of this method is that it could make the inventory even bigger. However, it would be possible to put these in group_vars files.

Alternatives to be discussed
It would also be possible to get the shared variable in the defaults file of each role, for example:
cephadm_hostname: "{{ hostname | default(null) }}"
But I find it less convenient.

It is also possible to put that in the playbook variables, but:

• It would be impossible for the user to overwrite it, as task vars have precedence over inventory (see Ansible docs).
• It would probably confuse people trying to launch the role themselves, IMO.

- name: Cephadm
  hosts:
      cluster_machines
  become: true
  vars:
    cephadm_hostname: "{{ hostname }}"
    cephadm_ip_addr: "{{ cluster_ip_addr }}"
  roles:
    - detect_seapath_distro
    - cephadm
    - deploy_cephfs

I'm open to discussion, mostly on choosing between inventories vs task vars.

[SkytAsul]

1st solution looks good to me, I would even advocate for putting the role-specific variables in a separate group vars file and only keep the "general" variable in the inventory file.
For instance, instead of this in the inventory:

# host vars
cluster_ip_addr: "192.168.55.1"
# group vars
networkd_systemdnetworkd_ip_addr: "{{ cluster_ip_addr }}"
cephadm_ip_addr: "{{ cluster_ip_addr }}"

We would get in the group vars:

networkd_systemdnetworkd_ip_addr: "{{ cluster_ip_addr }}"
cephadm_ip_addr: "{{ cluster_ip_addr }}"

And in the host vars in the inventory, we would only have:

cluster_ip_addr: "192.168.55.1"

That's 2 less lines in the inventory, and if the users ever need to tweak the value of each role var, they can still add them to their inventory file and it will take precedence.

[dupremathieu]

Agree. I prefer the 1st solution.

[eroussy]

See first example of this method in: #906