How to change play_hosts from playbook - ansible

Question

I have a file with two playbooks. Inventory is generated dynamically and there is no possibility to change it before starting playbook.
Run with command:
ansible-playbook -b adapter.yml --limit=host_group
adapter.yml
- name: Prepare stage
hosts: all
# The problem is that the inventory contains hosts in the format "x.x.x.x" ie physical address.
# I need to run a third-party role.
# But, it needs hosts in the format "instance-alias", that is, the name of the instance.
tasks:
# for this I create a new host group
- name: Add host in new format
add_host:
name: "{{ item.alias }}"
host: "{{ item.ansible_host }}"
groups: new_format_hosts
with_items: "{{ groups.all }}"
# I create a new play host group that matches the previous one in a new format
- name: Compose new play_hosts group
add_host:
name: "{{ item.alias }}"
groups: new_play_hosts
when: item.ansible_host in play_hosts
with_items: "{{ groups.all }}"
- name: Management stage
hosts: new_format_hosts
# in this playbook I want to change the composition
# of the target hosts and launch an external role
vars:
hostvars: "{{ hostvars }}"
play_hosts: "{{ groups.new_play_hosts }}" # THIS DONT WORK
- name: Run external role
import_role:
name: role_name
tasks_from: file_name
But I can’t change play_hosts so that the launched role uses only new hosts.
How to fix it?

Answer 1

This works for me:
- name: Prepare stage
hosts: localhost
tasks:
- name: Show hostavers
debug:
msg: "{{ hostvars[item]['ansible_host'] }}"
with_items: "{{ groups.all }}"
# for this I create a new host group
- name: Add host in new format
add_host:
name: "{{ hostvars[item].alias }}"
ansible_host: "{{ hostvars[item].ansible_host }}"
groups: new_format_hosts
with_items: "{{ groups.all }}"
- name: Management stage
hosts: new_format_hosts
tasks:
- name: Ping New Format Hosts
ping:
- name: Show ansible_host for each host
debug:
var: ansible_host
- name: Show playhosts
debug:
var: play_hosts
delegate_to: localhost
run_once: yes
This assumes, of course, that alias and ansible_host are set for all the hosts.
The hosts were:
AnsibleTower ansible_host=192.168.124.8 alias=fred
192.168.124.111 ansible_host=192.168.124.111 alias=barney
jaxsatB ansible_host=192.168.124.111 alias=wilma
The relevant output of the playbook was:
PLAY [Management stage] *****************************************************************************************************************************************************************
TASK [Gathering Facts] ******************************************************************************************************************************************************************
Friday 29 May 2020 18:09:26 -0400 (0:00:00.057) 0:00:01.332 ************
ok: [fred]
ok: [barney]
ok: [wilma]
TASK [New Format Hosts] *****************************************************************************************************************************************************************
Friday 29 May 2020 18:09:30 -0400 (0:00:04.308) 0:00:05.641 ************
ok: [barney]
ok: [wilma]
ok: [fred]
TASK [Show ansible_host] ****************************************************************************************************************************************************************
Friday 29 May 2020 18:09:30 -0400 (0:00:00.450) 0:00:06.091 ************
ok: [fred] => {
"ansible_host": "192.168.124.8"
}
ok: [barney] => {
"ansible_host": "192.168.124.111"
}
ok: [wilma] => {
"ansible_host": "192.168.124.111"
}
TASK [Show playhosts] *******************************************************************************************************************************************************************
Friday 29 May 2020 18:09:30 -0400 (0:00:00.109) 0:00:06.200 ************
ok: [fred -> localhost] => {
"play_hosts": [
"fred",
"barney",
"wilma"
]
}
PLAY RECAP ******************************************************************************************************************************************************************************
barney : ok=3 changed=0 unreachable=0 failed=0
fred : ok=4 changed=0 unreachable=0 failed=0
localhost : ok=3 changed=1 unreachable=0 failed=0
wilma : ok=3 changed=0 unreachable=0 failed=0
Friday 29 May 2020 18:09:30 -0400 (0:00:00.030) 0:00:06.231 ************
===============================================================================
You do not need to set the play_hosts variable. That is set by the line hosts: new_format_hosts in the second play.