Define list of dictionaries based on jinja conditionals in an ansible role

I'm creating an ansible role and I want to define my defaults in the following manner as an example:

include_mas_mount: false
include_log_mount: false

mounts:
  - name: 1st default mount
    mountdir: /data/mount1
    nasdir: /vol1/mount1
  - name: 2nd default mount
    mountdir: /data/mount2
    nasdir: /vol1/mount2
{% if include_mas_mount %}
  - name: mas mount
    mountdir: /data/mas_mount
    nasdir: /vol1/mas_mount
{% endif %}
{% if include_log_mount %}
  - name: log mount
    mountdir: /data/log_mount
    nasdir: /vol1/log_mount
{% endif %}

In testing this role I get a jinja templating error. Is this sort of thing possible? Or does it have be done differently. The idea with the role is that the include_mas_mount and include_log_mount variables would be overridden by a host or group override.

The role is expected to loop over the mounts: list of dictionaries and create the defined mounts on the target device.

Solution

You can quickfix the above by slightly changing your mounts definition:

mounts: |-
  {% filter from_yaml %}
  - name: 1st default mount
    mountdir: /data/mount1
    nasdir: /vol1/mount1
  - name: 2nd default mount
    mountdir: /data/mount2
    nasdir: /vol1/mount2
  {% if include_mas_mount %}
  - name: mas mount
    mountdir: /data/mas_mount
    nasdir: /vol1/mas_mount
  {% endif %}
  {% if include_log_mount %}
  - name: log mount
    mountdir: /data/log_mount
    nasdir: /vol1/log_mount
  {% endif %}
  {% endfilter %}

Meanwhile, this is not the best approach for at least 2 reasons:

You are using a 'complex' template for a variable definition when it is not needed nor justified and we tend to avoid this in ansible when possible.
You define mounts in defaults/main.yml although (from your description) you do not want users to override that variable directly.

The following will give the exact same result fixing the above problems. I used the name my_role for the role

First, we keep in roles/my_role/defaults/main.yml only the variables which will be user overridable:

---
include_mas_mount: false
include_log_mount: false

Then we create the following roles/my_role/vars/main.yml which contains roles variables we do not want users to play with:

---
mas_mount:
  name: mas mount
  mountdir: /data/mas_mount
  nasdir: /vol1/mas_mount

log_mount:
  name: log mount
  mountdir: /data/log_mount
  nasdir: /vol1/log_mount

default_mounts:
  - name: 1st default mount
    mountdir: /data/mount1
    nasdir: /vol1/mount1
  - name: 2nd default mount
    mountdir: /data/mount2
    nasdir: /vol1/mount2

mounts: "{{ default_mounts
  + ([log_mount] if include_log_mount | bool else [])
  + ([mas_mount] if include_mas_mount | bool else []) }}"

In the above, the use of bool is a best practice to make sure the value is interpreted as a boolean as users may override your variable with content that otherwise translates to a string (like e.g. when using a vars_prompt)

For the tests, I created the following dummy roles/my_role/tasks/main.yml

---
- name: Debug mounts var
  ansible.builtin.debug:
    var: mounts

and ran the role from the following playbook.yml:

---
- name: Test my conditional list in role
  hosts: localhost
  gather_facts: false

  roles:
    - name: my_role
    - name: my_role
      vars:
        include_mas_mount: true
    - name: my_role
      vars:
        include_log_mount: true
    - name: my_role
      vars:
        include_mas_mount: true
        include_log_mount: true

Which gives:

$ ansible-playbook playbook.yml 

PLAY [Test my conditional list in role] ****************************************************************************************************************************************************************************************

TASK [my_role : Debug mounts var] **********************************************************************************************************************************************************************************************
ok: [localhost] => {
    "mounts": [
        {
            "mountdir": "/data/mount1",
            "name": "1st default mount",
            "nasdir": "/vol1/mount1"
        },
        {
            "mountdir": "/data/mount2",
            "name": "2nd default mount",
            "nasdir": "/vol1/mount2"
        }
    ]
}

TASK [my_role : Debug mounts var] **********************************************************************************************************************************************************************************************
ok: [localhost] => {
    "mounts": [
        {
            "mountdir": "/data/mount1",
            "name": "1st default mount",
            "nasdir": "/vol1/mount1"
        },
        {
            "mountdir": "/data/mount2",
            "name": "2nd default mount",
            "nasdir": "/vol1/mount2"
        },
        {
            "mountdir": "/data/mas_mount",
            "name": "mas mount",
            "nasdir": "/vol1/mas_mount"
        }
    ]
}

TASK [my_role : Debug mounts var] **********************************************************************************************************************************************************************************************
ok: [localhost] => {
    "mounts": [
        {
            "mountdir": "/data/mount1",
            "name": "1st default mount",
            "nasdir": "/vol1/mount1"
        },
        {
            "mountdir": "/data/mount2",
            "name": "2nd default mount",
            "nasdir": "/vol1/mount2"
        },
        {
            "mountdir": "/data/log_mount",
            "name": "log mount",
            "nasdir": "/vol1/log_mount"
        }
    ]
}

TASK [my_role : Debug mounts var] **********************************************************************************************************************************************************************************************
ok: [localhost] => {
    "mounts": [
        {
            "mountdir": "/data/mount1",
            "name": "1st default mount",
            "nasdir": "/vol1/mount1"
        },
        {
            "mountdir": "/data/mount2",
            "name": "2nd default mount",
            "nasdir": "/vol1/mount2"
        },
        {
            "mountdir": "/data/log_mount",
            "name": "log mount",
            "nasdir": "/vol1/log_mount"
        },
        {
            "mountdir": "/data/mas_mount",
            "name": "mas mount",
            "nasdir": "/vol1/mas_mount"
        }
    ]
}

PLAY RECAP *********************************************************************************************************************************************************************************************************************
localhost                  : ok=4    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0