Ansible, Issue while using variable content in playbook - ansible

Question

I need to use variable defined for some hosts (in inventory), on another host.
Here i define it in my inventory
[mygroup:vars]
service_url=my_front_url
Where mygroup contain other groups, containing my hosts.
Then my playbook :
- name: Get variable
hosts: 127.0.0.1
tasks:
- debug:
var: hostvars[groups['{{ platform }}'][0]]['service_url']
- debug:
msg: "{{ hostvars[groups['\"{{ platform }}\"'][0]]['service_url'] }}"
Where platform is an extra-var (setting which "mygroup" to use)
and where 127.0.0.1 is my ansible host, distinct from my target hosts.
ex:
ansible-playbook test.yaml --extra-vars='platform=my-group'
TASK [debug] ********************************************************************************************************************************************************************
ok: [127.0.0.1] => {
"hostvars[groups['idi_se_prod'][0]]['service_url']": "my-front-url"
}
TASK [debug] ********************************************************************************************************************************************************************
fatal: [127.0.0.1]: FAILED! => {"msg": "The task includes an option with an undefined variable. The error was: 'dict object' has no attribute '\"{{ platform }}\"'\n\nThe error appears to have been in 'XXXX/ansible/test.yaml': line 6, column 5, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n var: hostvars[groups['{{ platform }}'][0]]['service_url']\n - debug:\n ^ here\n"}
If i set static group name in yaml, this work fine.
- name: Get variable
hosts: 127.0.0.1
tasks:
- debug:
var: hostvars[groups['{{ platform }}'][0]]['service_url']
- debug:
msg: "{{ hostvars[groups['mygroup'][0]]['service_url'] }}"
TASK [debug] ********************************************************************************************************************************************************************
ok: [127.0.0.1] => {
"hostvars[groups['my-group'][0]]['service_url']": "my-front-url"
}
TASK [debug] ********************************************************************************************************************************************************************
ok: [127.0.0.1] => {
"msg": "my_front_url"
}
It look like a syntax probleme but i tried so many ways that i think i could use some help.
Thank you
Nicolas

Answer 1

Everything inside {{ and }} is more or less just python, so don't use recursive templates like you have:
msg: "{{ hostvars[groups['\"{{ platform }}\"'][0]]['service_url'] }}"
instead just reference the variable like it is, a variable:
msg: "{{ hostvars[groups[platform][0]]['service_url'] }}"