Run ansible task if the client is not in ad domain

Currently I am creating a playbook to automate our initial server setup for ubuntu server 20.04.4 LTS. I've created the following simple task:

  - name: Join Domain domain.group
    expect:
      command: realm join -U domainuser domain.group
      responses:
        Password for *: "{{domain_join_pw}}"

This works just fine, but once the task is done and I run the play again it gets interrupted with the following message:

["realm: Already joined to this domain"]

Is there a way to check if the client is already in the domain and only run the task when it's not?

I tried the ansible_fqdn and ansible_domain fact like this:

  - name: Join Domain domain.group
    expect:
      command: realm join -U domainuser domain.group
      responses:
        Password for *: "{{domain_join_pw}}"
    when: ansible_fqdn != "domain.group"

I am quite new to Ansible, I think it's not hard to do but can't find out how. Thanks for every awnser.

It is assumed that the domain is registered within a variable.

DOMAIN: "domain.group"

You could use the following generic and not yet tested example to enhance your use case.

- name: Check if system is already domain joined
  shell:
    cmd: realm list | grep {{ DOMAIN }}
  changed_when: false
  check_mode: false
  register: domain_joined
  failed_when: domain_joined.rc !=0 and domain_joined.rc !=1

and let tasks later run only when not domain joined, in example

when: not domain_joined | bool

... currently I have domain joined systems only, therefore I could not run a full test with a not joined system yet.

You may have also a look into the command

sssctl domain-status ${DOMAIN}
Online status: Online

Active servers:
AD Global Catalog: not connected
AD Domain Controller: ad.example.com

Discovered AD Global Catalog servers:
None so far.

Discovered AD Domain Controller servers:
- ad.example.com

or {{ DOMAIN }} when used from within Ansible, check the output as well how to filter and register the result for further usage.