How do I specify encrypted strings in molecule group_vars? (could not determine a constructor for the tag '!vault')

I have these encrypted strings in my role's var/main.yml file ...

---
# vars 
wiki_password: !vault |
          $ANSIBLE_VAULT;1.1;AES256
          63343237 ... omitted for brevity ...

... and everything works fine. BUT I was told that I need to not define this in the my_role/vars/main.yml file but in the groups_vars. So for my unit test I updated my molecule/defaults/molecule.yml file:

... omitted ...

provisioner:
  name: ansible
  inventory:
    group_vars:
      all:
        ... other vars ...
        web_domain: "example.com"

        wiki_password: !vault |
          $ANSIBLE_VAULT;1.1;AES256
          63343237 ... omitted for brevity ...    
          
... omitted ...

But now when I run molecule test I get this error:

yaml.constructor.ConstructorError: could not determine a constructor for the tag '!vault'
  in "<unicode string>", line 50, column 28:
            wiki_password: !vault |

Solution

vault is an Ansible feature, not a molecule feature. Molecule needs to load and validate its configuration file and by the time it reaches your vault string, ansible has not come into play yet.

One way to workaround your above problem is to use the links feature in the provisioner config (see the ansible provisioner documentation). In this case the variable will only be read by the time ansible launches and not when molecule is trying to create the corresponding inventory files.

As an example, here is a test I just made from scratch:

Init a role with molecule

molecule init role acme.so_demo -d docker
cd so_demo

Create the inventory group file

mkdir -p molecule/.inventory/group_vars/
echo -en "---\ntoto: $(ansible-vault encrypt_string --encrypt-vault-id your_id some_value)" > molecule/.inventory/group_vars/all.yml

Which gives as a result in molecule/.inventory/group_vars/all.yml

---
toto: !vault |
          $ANSIBLE_VAULT;1.2;AES256;your_id
          38323137303132393932623963326164643834386333626166633734653338313331303331313638
          ...

Edit the provisioner config. This is how my molecule/default/molecule.yml looks like:

---
dependency:
  name: galaxy
driver:
  name: docker
platforms:
  - name: instance
    image: quay.io/centos/centos:stream8
    pre_build_image: true
provisioner:
  name: ansible
  inventory:
    links:
      group_vars: ../.inventory/group_vars/
verifier:
  name: ansible

Add a dummy task in tasks/main.yml

---
- name: Debug vault var
  ansible.builtin.debug:
    var: toto

You can now run the example with

molecule converge

Which gives (abridged):

PLAY [Converge] ****************************************************************

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

TASK [Include acme.so_demo] ****************************************************

TASK [acme.so_demo : Debug vault var] ******************************************
ok: [instance] => {
    "toto": "some_value"
}

PLAY RECAP *********************************************************************
instance                   : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0