How to check the OS version of host which in dynamically added to inventory - ansible

Question

I'm trying to get server name as user input and if the server OS is RHEL7 it will proceed for further tasks. I'm trying with hostvars but it is not helping, kindly help me to find the OS version with when condition:
---
- name: Add hosts
hosts: localhost
vars:
- username: test
password: test
vars_prompt:
- name: server1
prompt: Server_1 IP or hostname
private: no
- name: server2
prompt: Server_2 IP or hostname
private: no
tasks:
- add_host:
name: "{{ server1 }}"
groups:
- cluster_nodes
- primary
- management
ansible_user: "{{ username }}"
ansible_password: "{{ password}}"
- add_host:
name: "{{ server2 }}"
groups:
- cluster_nodes
- secondary
ansible_user: "{{ username }}"
ansible_password: "{{ password}}"
- debug:
msg: "{{ hostvars['server1'].ansible_distribution_major_version }}"
When I execute the playbook, I'm getting below error:
fatal: [localhost]: FAILED! => {"msg": "The task includes an option with an undefined variable. The error was: \"hostvars['server1']\" is undefined\n\nThe error appears to be in '/var/lib/awx/projects/pacemaker_RHEL_7_ST/main_2.yml': line 33, column 7, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n\n - debug:\n ^ here\n"}

Answer 1

You need to gather_facts on the newly added host before you consume the variable. As an example, this will do it with automatic facts gathering.
---
- name: Add hosts
hosts: localhost
vars:
- username: test
password: test
vars_prompt:
- name: server1
prompt: Server_1 IP or hostname
private: no
- name: server2
prompt: Server_2 IP or hostname
private: no
tasks:
- add_host:
name: "{{ server1 }}"
groups:
- cluster_nodes
- primary
- management
ansible_user: "{{ username }}"
ansible_password: "{{ password}}"
- add_host:
name: "{{ server2 }}"
groups:
- cluster_nodes
- secondary
ansible_user: "{{ username }}"
ansible_password: "{{ password}}"
- name: Gather facts for newly added targets
hosts: cluster_nodes
# gather_facts: true <= this is the default
- name: Do <whatever> targeting localhost again
hosts: localhost
gather_facts: false # already gathered in play1
tasks:
# Warning!! bad practice. Looping on a group usually
# shows you should have a play targeting that specific group
- debug:
msg: "OS version for {{ item }} is 7"
when: hostvars[item].ansible_distribution_major_version | int == 7
loop: "{{ groups['cluster_nodes'] }}"
If you don't want to rely on automatic gathering, you can manually play the setup module, e.g. for the second play:
- name: Gather facts for newly added targets
hosts: cluster_nodes
gather_facts: false
tasks:
- name: get facts from targets
setup: