Ansible: Add Unix group to user only if the group exists - unix

Question

I'm using Ansible to add a user to a variety of servers. Some of the servers have different UNIX groups defined. I'd like to find a way for Ansible to check for the existence of a group that I specify, and if that group exists, add it to a User's secondary groups list (but ignore the statement it if the group does not exist).
Any thoughts on how I might do this with Ansible?
Here is my starting point.
Command
ansible-playbook -i 'localhost,' -c local ansible_user.yml
ansible_user.yml
---
- hosts: all
user: root
become: yes
vars:
password: "!"
user: testa
tasks:
- name: add user
user: name="{{user}}"
state=present
password="{{password}}"
shell=/bin/bash
append=yes
comment="test User"
Updated: based on the solution suggested by #udondan, I was able to get this working with the following additional tasks.
- name: Check if user exists
shell: /usr/bin/getent group | awk -F":" '{print $1}'
register: etc_groups
- name: Add secondary Groups to user
user: name="{{user}}" groups="{{item}}" append=yes
when: '"{{item}}" in etc_groups.stdout_lines'
with_items:
- sudo
- wheel

Answer 1

The getent module can be used to read /etc/group
- name: Determine available groups
getent:
database: group
- name: Add additional groups to user
user: name="{{user}}" groups="{{item}}" append=yes
when: item in ansible_facts.getent_group
with_items:
- sudo
- wheel

Answer 2

Do you have anything to identify those different host types?
If not, you first need to check which groups exist on that host. You can do this with the command getent group | cut -d: -f1 which will output one group per line.
You can use this as separate task like so:
- shell: getent group | cut -d: -f1
register: unix_groups
The registered result then can be used later when you want to add the user group
- user: ...
when: "'some_group' in unix_groups.stdout_lines"

Answer 3

This is how I'm dealing with this in my playbooks. The idea is simple - to take a list of existing groups and find an intersection between groups a user wants to be member of and groups that exist:
- name: Get Existing Groups
getent:
database: group
- name: Configure Users
user:
name: username
groups: "{{ ['wheel', 'docker', 'video'] | intersect(ansible_facts['getent_group'] | list) }}"
The getent module outputs the 'getent_group' Ansible fact containing all existing groups with their details. By piping it to | list filter I get plain list of group names. The intersect filter finds what's common between two lists.
One of the advantages of this solution is that I don't have to use append parameter of the user module. This way user may be correctly removed from groups that I don't want it to be member of anymore.

Answer 4

I had the similar requirement, then I did the followings,
ansible [core 2.12.2]
---
- hosts: all
become: yes
become_user: root
tasks:
- ansible.builtin.user:
name: test1
password: "&&**%%^^"
uid: 1234
shell: /bin/bash
- ansible.builtin.shell:
"cat /etc/group| grep -o sysadmin"
register: output
#you can omit the debug part
- debug:
var: output
- name: assign user the group
ansible.builtin.shell:
"usermod -G sysadmin test1"
when: "'sysadmin' in output.stdout_lines"
Update: Thanks for the suggestion #Jeter-work
- hosts: localhost
tasks:
- name: Get all groups
ansible.builtin.getent:
database: group
split: ':'
- debug:
var: ansible_facts.getent_group