Insert host in to group_vars when playbook is run

How to set host1 in to group_vars database from playbook has run?

Thanks

Solution

The short answer is: ansible.builtin.add_host

But, it's good to know that this change won't affect the current play. For example, given the inventory

shell> cat hosts
[database]
host2
host3

and the group_vars

shell> cat group_vars/database/main.yml 
test_var: database

The below play

- name: Play 1
  hosts: database

  tasks:

    - debug:
        var: groups
      run_once: true

    - debug:
        var: test_var

gives as expected (abridged)

TASK [debug] ***
ok: [host2] => 
  groups:
    all:
    - host2
    - host3
    database:
    - host2
    - host3
    ungrouped: []

TASK [debug] ***
ok: [host2] => 
  test_var: database
ok: [host3] => 
  test_var: database

If you add the host host1 to the group database

    - add_host:
        name: host1
        groups: database

the added host will be reported in the group immediately

    - debug:
        var: groups
      run_once: true

gives (abridged)

  groups:
    all:
    - host1
    - host2
    - host3
    database:
    - host2
    - host3
    - host1
    ungrouped: []

But, the added host won't be included in the execution of the play

    - debug:
        var: test_var

gives (abridged) the same result as before

ok: [host2] => 
  test_var: database
ok: [host3] => 
  test_var: database

Refreshing the inventory doesn't help

    - meta: refresh_inventory

    - debug:
        var: test_var

still gives the same result

ok: [host2] => 
  test_var: database
ok: [host3] => 
  test_var: database

You have to start a new play to include the new host in the group

- name: Play 2
  hosts: database

  tasks:

    - debug:
        var: test_var

gives

ok: [host2] => 
  test_var: database
ok: [host3] => 
  test_var: database
ok: [host1] => 
  test_var: database

The addition of the host to the group is not permanent. Only the current playbook is affected.

^{Example of a complete playbook for testing.
- name: Play 1
hosts: database

tasks:

- debug:
var: groups
run_once: true

- debug:
var: test_var

- add_host:
name: host1
groups: database

- debug:
var: groups
run_once: true

- debug:
var: test_var

- meta: refresh_inventory

- debug:
var: test_var

- name: Play 2
hosts: database

tasks:

- debug:
var: test_var}