How to dynamically set the hosts field in Ansible playbooks with a variable generated during execution? - variables

Question

I am trying to test something at home with the variables mechanism Ansible offers, which I am about to implement in one of my projects at work. So, been searching for a while now, but seems I can't get it working that easily, even with others` solutions here and there.
I will represent my project logic at work now, by demonstrating with my test directory & files structure at home. Here's the case, I have the following playbooks:
main.yaml
pl1.yaml
pl2.yaml
Contents of ./main.yaml:
- import_playbook: /home/martin/ansible/pl1.yaml
- import_playbook: /home/martin/ansible/pl2.yaml
Contents of ./pl1.yaml:
- name: Test playbook 1
hosts: localhost
tasks:
- name: Discovering the secret host
shell: cat /home/martin/secret
register: whichHostAd
- debug:
msg: "{{ whichHostAd.stdout }}"
- name: Discovering my hostname
shell: hostname
register: myHostnameAd
- set_fact:
whichHost: "{{ whichHostAd.stdout }}"
myHostname: "{{ myHostnameAd.stdout }}"
cacheable: yes
- name: Test playbook 1 part 2
hosts: "{{ hostvars['localhost']['ansible_facts']['whichHost'] }}"
tasks:
- name: Structuring info
shell: hostname
register: secretHostname
- name: Showing the secret hostname
debug:
msg: "{{ secretHostname.stdout }}"
Contents of ./pl2.yaml:
- name: Test Playbook 2
hosts: "{{ whichHost }}"
tasks:
- name: Finishing up
shell: echo "And here am i again.." && hostname
- name: Showing var myHostname
debug:
msg: "{{ myHostname.stdout }}"
The whole idea is to have a working variable on the go at the hosts field between the plays. How do we do that?
The playbook does not run at all if I won't define the whichHost variable as an extra arg, and that's ok, I can do it each time, but during the execution I would like to have that variable manageable and changeable. In the test case above, I want whichHost to be used everywhere across the plays/playbooks included in main.yaml, specifically to reflect the output of the first task in pl1.yaml (or the output of the whichHostAd.stdout variable), so I can determine the host I am about to target in pl2.yaml.
According to docs, I should be able to at least access it with hostvars (as in my playbook), but this is the output I get when I try the above example:
ERROR! The field 'hosts' has an invalid value, which includes an undefined variable. The error was: 'dict object' has no attribute 'whichHost'
The error appears to have been in '/home/martin/ansible/pl1.yaml': line 22, column 3, but may
be elsewhere in the file depending on the exact syntax problem.
The offending line appears to be:
- name: Test playbook 1 part 2
^ here
set_fact also does not seem to be very helpful. Any help will be appreciated!

Answer 1

Ok, I've actually figured it out pretty fast.
So, we definitely need to have a fact task, holding the actual data/output:
- hosts: localhost
tasks:
- name: Saving variable
set_fact:
whichHost: "{{ whichHostAd.stdout }}"
After that, when you want to invoke the var in other hosts and plays, we have to provide the host and the fact:
"{{ hostvars['localhost']['whichHost'] }}"
Like in my test above, but without ['ansible_facts']